| Message ID | 81e1307108ca8ea67aa1060f6f47b34a507410f1.1605235762.git.pcc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: expose FAR_EL1 tag bits in siginfo | expand |
Peter Collingbourne <pcc@google.com> writes: > The kernel currently clears the tag bits (i.e. bits 56-63) in the fault > address exposed via siginfo.si_addr and sigcontext.fault_address. However, > the tag bits may be needed by tools in order to accurately diagnose > memory errors, such as HWASan [1] or future tools based on the Memory > Tagging Extension (MTE). > > We should not stop clearing these bits in the existing fault address > fields, because there may be existing userspace applications that are > expecting the tag bits to be cleared. Instead, introduce a flag in > sigaction.sa_flags, SA_EXPOSE_TAGBITS, and only expose the tag bits > there if the signal handler has this flag set. For future architectures that implement something similar does it make sense that to hide tag bits by default? I am wondering if SA_EXPOSE_TABGITS might make sense as an architecture specific sa bit. Otherwise this patch looks good to me. Eric > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > Signed-off-by: Peter Collingbourne <pcc@google.com> > Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 > --- > v16: > - add missing file > > v15: > - switched to the SA_EXPOSE_TAGBITS approach > proposed by Eric > - rebased to 5.10-rc3 > > v14: > - fix an inaccuracy in the commit message > - add some comments to arch_addr_tag_bits_mask > > v13: > - renamed si_xflags to si_faultflags > - rebased to 5.10-rc2 > > v12: > - add new fields to signal_compat.c test cases > - rebased to 5.10-rc1 > - mask out bits 63:60 for tag check faults > > v11: > - add a comment explaining what the arch hook should do > - rename ignored bits to tag bits > > v10: > - rename the flag to SIFAULTFLAG_ADDR_IGNORED_BITS > - use an arch hook to specify which bits are ignored, instead > of passing them explicitly > - while refactoring for the arch hook, noticed that my previous > patches missed a case involving cache maintenance instructions, > so expose the tag bits for that signal as well > > v9: > - make the ignored bits fields generic > - add some new dependent patches that prepare us to store the > field in such a way that userspace can detect their presence > > v8: > - rebase onto 5.8rc2 > > v7: > - switch to a new siginfo field instead of using sigcontext > - merge the patch back into one since the other patches are now > unnecessary > > v6: > - move fault address and fault code into the kernel_siginfo data structure > - split the patch in three since it was getting large and now has > generic and arch-specific parts > > v5: > - add padding to fault_addr_top_byte_context in order to ensure the correct > size and preserve sp alignment > > v4: > - expose only the tag bits in the context instead of the entire FAR_EL1 > - remove mention of the new context from the sigcontext.__reserved[] note > > v3: > - add documentation to tagged-pointers.rst > - update comments in sigcontext.h > > v2: > - revert changes to hw_breakpoint.c > - rename set_thread_esr to set_thread_far_esr > > Documentation/arm64/tagged-pointers.rst | 25 ++++++--- > arch/arm64/include/asm/exception.h | 2 +- > arch/arm64/include/asm/signal.h | 25 +++++++++ > arch/arm64/include/asm/system_misc.h | 2 +- > arch/arm64/include/asm/traps.h | 6 +-- > arch/arm64/kernel/debug-monitors.c | 5 +- > arch/arm64/kernel/entry-common.c | 2 - > arch/arm64/kernel/ptrace.c | 7 +-- > arch/arm64/kernel/sys_compat.c | 5 +- > arch/arm64/kernel/traps.c | 29 ++++++----- > arch/arm64/mm/fault.c | 68 ++++++++++++++----------- > include/linux/signal.h | 14 +++++ > include/linux/signal_types.h | 2 +- > include/uapi/asm-generic/signal-defs.h | 3 ++ > kernel/signal.c | 23 ++++++--- > 15 files changed, 141 insertions(+), 77 deletions(-) > create mode 100644 arch/arm64/include/asm/signal.h > > diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > index eab4323609b9..19d284b70384 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -53,12 +53,25 @@ visibility. > Preserving tags > --------------- > > -Non-zero tags are not preserved when delivering signals. This means that > -signal handlers in applications making use of tags cannot rely on the > -tag information for user virtual addresses being maintained for fields > -inside siginfo_t. One exception to this rule is for signals raised in > -response to watchpoint debug exceptions, where the tag information will > -be preserved. > +When delivering signals, non-zero tags are not preserved in > +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > +sigaction.sa_flags when the signal handler was installed. This means > +that signal handlers in applications making use of tags cannot rely > +on the tag information for user virtual addresses being maintained > +in these fields unless the flag was set. > + > +Due to architecture limitations, bits 63:60 of the fault address > +are not preserved in response to synchronous tag check faults > +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > +treat the values of these bits as undefined in order to accommodate > +future architecture revisions which may preserve the bits. > + > +For signals raised in response to watchpoint debug exceptions, the > +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > +flag setting. > + > +Non-zero tags are never preserved in sigcontext.fault_address > +regardless of the SA_EXPOSE_TAGBITS flag setting. > > The architecture prevents the use of a tagged PC, so the upper byte will > be set to a sign-extension of bit 55 on exception return. > diff --git a/arch/arm64/include/asm/exception.h b/arch/arm64/include/asm/exception.h > index 99b9383cd036..2a8aa1884d8a 100644 > --- a/arch/arm64/include/asm/exception.h > +++ b/arch/arm64/include/asm/exception.h > @@ -32,7 +32,7 @@ static inline u32 disr_to_esr(u64 disr) > } > > asmlinkage void enter_from_user_mode(void); > -void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs); > +void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs); > void do_undefinstr(struct pt_regs *regs); > void do_bti(struct pt_regs *regs); > asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr); > diff --git a/arch/arm64/include/asm/signal.h b/arch/arm64/include/asm/signal.h > new file mode 100644 > index 000000000000..ef449f5f4ba8 > --- /dev/null > +++ b/arch/arm64/include/asm/signal.h > @@ -0,0 +1,25 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef __ARM64_ASM_SIGNAL_H > +#define __ARM64_ASM_SIGNAL_H > + > +#include <asm/memory.h> > +#include <uapi/asm/signal.h> > +#include <uapi/asm/siginfo.h> > + > +static inline void __user *arch_untagged_si_addr(void __user *addr, > + unsigned long sig, > + unsigned long si_code) > +{ > + /* > + * For historical reasons, all bits of the fault address are exposed as > + * address bits for watchpoint exceptions. New architectures should > + * handle the tag bits consistently. > + */ > + if (sig == SIGTRAP && si_code == TRAP_BRKPT) > + return addr; > + > + return untagged_addr(addr); > +} > +#define arch_untagged_si_addr arch_untagged_si_addr > + > +#endif > diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h > index 1ab63cfbbaf1..673be2d1263c 100644 > --- a/arch/arm64/include/asm/system_misc.h > +++ b/arch/arm64/include/asm/system_misc.h > @@ -22,7 +22,7 @@ void die(const char *msg, struct pt_regs *regs, int err); > > struct siginfo; > void arm64_notify_die(const char *str, struct pt_regs *regs, > - int signo, int sicode, void __user *addr, > + int signo, int sicode, unsigned long far, > int err); > > void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned int, > diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h > index d96dc2c7c09d..54f32a0675df 100644 > --- a/arch/arm64/include/asm/traps.h > +++ b/arch/arm64/include/asm/traps.h > @@ -26,9 +26,9 @@ void register_undef_hook(struct undef_hook *hook); > void unregister_undef_hook(struct undef_hook *hook); > void force_signal_inject(int signal, int code, unsigned long address, unsigned int err); > void arm64_notify_segfault(unsigned long addr); > -void arm64_force_sig_fault(int signo, int code, void __user *addr, const char *str); > -void arm64_force_sig_mceerr(int code, void __user *addr, short lsb, const char *str); > -void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr, const char *str); > +void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str); > +void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str); > +void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str); > > /* > * Move regs->pc to next instruction and do necessary setup before it > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c > index fa76151de6ff..4f3661eeb7ec 100644 > --- a/arch/arm64/kernel/debug-monitors.c > +++ b/arch/arm64/kernel/debug-monitors.c > @@ -234,9 +234,8 @@ static void send_user_sigtrap(int si_code) > if (interrupts_enabled(regs)) > local_irq_enable(); > > - arm64_force_sig_fault(SIGTRAP, si_code, > - (void __user *)instruction_pointer(regs), > - "User debug trap"); > + arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs), > + "User debug trap"); > } > > static int single_step_handler(unsigned long unused, unsigned int esr, > diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c > index 43d4c329775f..dbbddfbf4a72 100644 > --- a/arch/arm64/kernel/entry-common.c > +++ b/arch/arm64/kernel/entry-common.c > @@ -22,7 +22,6 @@ static void notrace el1_abort(struct pt_regs *regs, unsigned long esr) > unsigned long far = read_sysreg(far_el1); > > local_daif_inherit(regs); > - far = untagged_addr(far); > do_mem_abort(far, esr, regs); > } > NOKPROBE_SYMBOL(el1_abort); > @@ -114,7 +113,6 @@ static void notrace el0_da(struct pt_regs *regs, unsigned long esr) > > user_exit_irqoff(); > local_daif_restore(DAIF_PROCCTX); > - far = untagged_addr(far); > do_mem_abort(far, esr, regs); > } > NOKPROBE_SYMBOL(el0_da); > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > index f49b349e16a3..8ac487c84e37 100644 > --- a/arch/arm64/kernel/ptrace.c > +++ b/arch/arm64/kernel/ptrace.c > @@ -192,14 +192,11 @@ static void ptrace_hbptriggered(struct perf_event *bp, > break; > } > } > - arm64_force_sig_ptrace_errno_trap(si_errno, > - (void __user *)bkpt->trigger, > + arm64_force_sig_ptrace_errno_trap(si_errno, bkpt->trigger, > desc); > } > #endif > - arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, > - (void __user *)(bkpt->trigger), > - desc); > + arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, bkpt->trigger, desc); > } > > /* > diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c > index 3c18c2454089..265fe3eb1069 100644 > --- a/arch/arm64/kernel/sys_compat.c > +++ b/arch/arm64/kernel/sys_compat.c > @@ -68,7 +68,7 @@ do_compat_cache_op(unsigned long start, unsigned long end, int flags) > */ > long compat_arm_syscall(struct pt_regs *regs, int scno) > { > - void __user *addr; > + unsigned long addr; > > switch (scno) { > /* > @@ -111,8 +111,7 @@ long compat_arm_syscall(struct pt_regs *regs, int scno) > break; > } > > - addr = (void __user *)instruction_pointer(regs) - > - (compat_thumb_mode(regs) ? 2 : 4); > + addr = instruction_pointer(regs) - (compat_thumb_mode(regs) ? 2 : 4); > > arm64_notify_die("Oops - bad compat syscall(2)", regs, > SIGILL, ILL_ILLTRP, addr, scno); > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index 8af4e0e85736..f4ddbe9ed3f1 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -170,32 +170,32 @@ static void arm64_show_signal(int signo, const char *str) > __show_regs(regs); > } > > -void arm64_force_sig_fault(int signo, int code, void __user *addr, > +void arm64_force_sig_fault(int signo, int code, unsigned long far, > const char *str) > { > arm64_show_signal(signo, str); > if (signo == SIGKILL) > force_sig(SIGKILL); > else > - force_sig_fault(signo, code, addr); > + force_sig_fault(signo, code, (void __user *)far); > } > > -void arm64_force_sig_mceerr(int code, void __user *addr, short lsb, > +void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, > const char *str) > { > arm64_show_signal(SIGBUS, str); > - force_sig_mceerr(code, addr, lsb); > + force_sig_mceerr(code, (void __user *)far, lsb); > } > > -void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr, > +void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, > const char *str) > { > arm64_show_signal(SIGTRAP, str); > - force_sig_ptrace_errno_trap(errno, addr); > + force_sig_ptrace_errno_trap(errno, (void __user *)far); > } > > void arm64_notify_die(const char *str, struct pt_regs *regs, > - int signo, int sicode, void __user *addr, > + int signo, int sicode, unsigned long far, > int err) > { > if (user_mode(regs)) { > @@ -203,7 +203,7 @@ void arm64_notify_die(const char *str, struct pt_regs *regs, > current->thread.fault_address = 0; > current->thread.fault_code = err; > > - arm64_force_sig_fault(signo, sicode, addr, str); > + arm64_force_sig_fault(signo, sicode, far, str); > } else { > die(str, regs, err); > } > @@ -374,7 +374,7 @@ void force_signal_inject(int signal, int code, unsigned long address, unsigned i > signal = SIGKILL; > } > > - arm64_notify_die(desc, regs, signal, code, (void __user *)address, err); > + arm64_notify_die(desc, regs, signal, code, address, err); > } > > /* > @@ -385,7 +385,7 @@ void arm64_notify_segfault(unsigned long addr) > int code; > > mmap_read_lock(current->mm); > - if (find_vma(current->mm, addr) == NULL) > + if (find_vma(current->mm, untagged_addr(addr)) == NULL) > code = SEGV_MAPERR; > else > code = SEGV_ACCERR; > @@ -448,12 +448,13 @@ NOKPROBE_SYMBOL(do_ptrauth_fault); > > static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs) > { > - unsigned long address; > + unsigned long tagged_address, address; > int rt = ESR_ELx_SYS64_ISS_RT(esr); > int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT; > int ret = 0; > > - address = untagged_addr(pt_regs_read_reg(regs, rt)); > + tagged_address = pt_regs_read_reg(regs, rt); > + address = untagged_addr(tagged_address); > > switch (crm) { > case ESR_ELx_SYS64_ISS_CRM_DC_CVAU: /* DC CVAU, gets promoted */ > @@ -480,7 +481,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs) > } > > if (ret) > - arm64_notify_segfault(address); > + arm64_notify_segfault(tagged_address); > else > arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE); > } > @@ -772,7 +773,7 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr) > */ > void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr) > { > - void __user *pc = (void __user *)instruction_pointer(regs); > + unsigned long pc = instruction_pointer(regs); > > current->thread.fault_address = 0; > current->thread.fault_code = esr; > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 1ee94002801f..c5375cb7763d 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -40,7 +40,7 @@ > #include <asm/traps.h> > > struct fault_info { > - int (*fn)(unsigned long addr, unsigned int esr, > + int (*fn)(unsigned long far, unsigned int esr, > struct pt_regs *regs); > int sig; > int code; > @@ -385,8 +385,11 @@ static void set_thread_esr(unsigned long address, unsigned int esr) > current->thread.fault_code = esr; > } > > -static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs) > +static void do_bad_area(unsigned long far, unsigned int esr, > + struct pt_regs *regs) > { > + unsigned long addr = untagged_addr(far); > + > /* > * If we are in kernel mode at this point, we have no context to > * handle this fault with. > @@ -395,8 +398,7 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re > const struct fault_info *inf = esr_to_fault_info(esr); > > set_thread_esr(addr, esr); > - arm64_force_sig_fault(inf->sig, inf->code, (void __user *)addr, > - inf->name); > + arm64_force_sig_fault(inf->sig, inf->code, far, inf->name); > } else { > __do_kernel_fault(addr, esr, regs); > } > @@ -448,7 +450,7 @@ static bool is_write_abort(unsigned int esr) > return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM); > } > > -static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > +static int __kprobes do_page_fault(unsigned long far, unsigned int esr, > struct pt_regs *regs) > { > const struct fault_info *inf; > @@ -456,6 +458,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > vm_fault_t fault; > unsigned long vm_flags = VM_ACCESS_FLAGS; > unsigned int mm_flags = FAULT_FLAG_DEFAULT; > + unsigned long addr = untagged_addr(far); > > if (kprobe_page_fault(regs, esr)) > return 0; > @@ -567,8 +570,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > * We had some memory, but were unable to successfully fix up > * this page fault. > */ > - arm64_force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr, > - inf->name); > + arm64_force_sig_fault(SIGBUS, BUS_ADRERR, far, inf->name); > } else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) { > unsigned int lsb; > > @@ -576,8 +578,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > if (fault & VM_FAULT_HWPOISON_LARGE) > lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); > > - arm64_force_sig_mceerr(BUS_MCEERR_AR, (void __user *)addr, lsb, > - inf->name); > + arm64_force_sig_mceerr(BUS_MCEERR_AR, far, lsb, inf->name); > } else { > /* > * Something tried to access memory that isn't in our memory > @@ -585,8 +586,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > */ > arm64_force_sig_fault(SIGSEGV, > fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR, > - (void __user *)addr, > - inf->name); > + far, inf->name); > } > > return 0; > @@ -596,33 +596,35 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, > return 0; > } > > -static int __kprobes do_translation_fault(unsigned long addr, > +static int __kprobes do_translation_fault(unsigned long far, > unsigned int esr, > struct pt_regs *regs) > { > + unsigned long addr = untagged_addr(far); > + > if (is_ttbr0_addr(addr)) > - return do_page_fault(addr, esr, regs); > + return do_page_fault(far, esr, regs); > > - do_bad_area(addr, esr, regs); > + do_bad_area(far, esr, regs); > return 0; > } > > -static int do_alignment_fault(unsigned long addr, unsigned int esr, > +static int do_alignment_fault(unsigned long far, unsigned int esr, > struct pt_regs *regs) > { > - do_bad_area(addr, esr, regs); > + do_bad_area(far, esr, regs); > return 0; > } > > -static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs) > +static int do_bad(unsigned long far, unsigned int esr, struct pt_regs *regs) > { > return 1; /* "fault" */ > } > > -static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) > +static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs) > { > const struct fault_info *inf; > - void __user *siaddr; > + unsigned long siaddr; > > inf = esr_to_fault_info(esr); > > @@ -635,18 +637,23 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) > } > > if (esr & ESR_ELx_FnV) > - siaddr = NULL; > + siaddr = 0; > else > - siaddr = (void __user *)addr; > + siaddr = untagged_addr(far); > arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr); > > return 0; > } > > -static int do_tag_check_fault(unsigned long addr, unsigned int esr, > +static int do_tag_check_fault(unsigned long far, unsigned int esr, > struct pt_regs *regs) > { > - do_bad_area(addr, esr, regs); > + /* > + * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag > + * check faults. Mask them out now so that userspace doesn't see them. > + */ > + far &= (1UL << 60) - 1; > + do_bad_area(far, esr, regs); > return 0; > } > > @@ -717,11 +724,12 @@ static const struct fault_info fault_info[] = { > { do_bad, SIGKILL, SI_KERNEL, "unknown 63" }, > }; > > -void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) > +void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs) > { > const struct fault_info *inf = esr_to_fault_info(esr); > + unsigned long addr = untagged_addr(far); > > - if (!inf->fn(addr, esr, regs)) > + if (!inf->fn(far, esr, regs)) > return; > > if (!user_mode(regs)) { > @@ -730,8 +738,7 @@ void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) > show_pte(addr); > } > > - arm64_notify_die(inf->name, regs, > - inf->sig, inf->code, (void __user *)addr, esr); > + arm64_notify_die(inf->name, regs, inf->sig, inf->code, addr, esr); > } > NOKPROBE_SYMBOL(do_mem_abort); > > @@ -744,8 +751,8 @@ NOKPROBE_SYMBOL(do_el0_irq_bp_hardening); > > void do_sp_pc_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) > { > - arm64_notify_die("SP/PC alignment exception", regs, > - SIGBUS, BUS_ADRALN, (void __user *)addr, esr); > + arm64_notify_die("SP/PC alignment exception", regs, SIGBUS, BUS_ADRALN, > + addr, esr); > } > NOKPROBE_SYMBOL(do_sp_pc_abort); > > @@ -871,8 +878,7 @@ void do_debug_exception(unsigned long addr_if_watchpoint, unsigned int esr, > arm64_apply_bp_hardening(); > > if (inf->fn(addr_if_watchpoint, esr, regs)) { > - arm64_notify_die(inf->name, regs, > - inf->sig, inf->code, (void __user *)pc, esr); > + arm64_notify_die(inf->name, regs, inf->sig, inf->code, pc, esr); > } > > debug_exception_exit(regs); > diff --git a/include/linux/signal.h b/include/linux/signal.h > index b256f9c65661..205526c4003a 100644 > --- a/include/linux/signal.h > +++ b/include/linux/signal.h > @@ -469,4 +469,18 @@ struct seq_file; > extern void render_sigset_t(struct seq_file *, const char *, sigset_t *); > #endif > > +#ifndef arch_untagged_si_addr > +/* > + * Given a fault address and a signal and si_code which correspond to the > + * _sigfault union member, returns the address that must appear in si_addr if > + * the signal handler does not have SA_EXPOSE_TAGBITS enabled in sa_flags. > + */ > +static inline void __user *arch_untagged_si_addr(void __user *addr, > + unsigned long sig, > + unsigned long si_code) > +{ > + return addr; > +} > +#endif > + > #endif /* _LINUX_SIGNAL_H */ > diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h > index a7887ad84d36..68e06c75c5b2 100644 > --- a/include/linux/signal_types.h > +++ b/include/linux/signal_types.h > @@ -78,6 +78,6 @@ struct ksignal { > > #define UAPI_SA_FLAGS \ > (SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART | \ > - SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS) > + SA_NODEFER | SA_RESETHAND | SA_EXPOSE_TAGBITS | __ARCH_UAPI_SA_FLAGS) > > #endif /* _LINUX_SIGNAL_TYPES_H */ > diff --git a/include/uapi/asm-generic/signal-defs.h b/include/uapi/asm-generic/signal-defs.h > index 0126ebda4d31..5276bdd4a9e2 100644 > --- a/include/uapi/asm-generic/signal-defs.h > +++ b/include/uapi/asm-generic/signal-defs.h > @@ -20,6 +20,8 @@ > * so this bit allows flag bit support to be detected from userspace while > * allowing an old kernel to be distinguished from a kernel that supports every > * flag bit. > + * SA_EXPOSE_TAGBITS exposes an architecture-defined set of tag bits in > + * siginfo.si_addr. > * > * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single > * Unix names RESETHAND and NODEFER respectively. > @@ -49,6 +51,7 @@ > #define SA_RESETHAND 0x80000000 > #endif > #define SA_UNSUPPORTED 0x00000400 > +#define SA_EXPOSE_TAGBITS 0x00000800 > > #define SA_NOMASK SA_NODEFER > #define SA_ONESHOT SA_RESETHAND > diff --git a/kernel/signal.c b/kernel/signal.c > index 8f34819e80de..16be62e6d341 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -1650,6 +1650,15 @@ void force_sigsegv(int sig) > force_sig(SIGSEGV); > } > > +static void __user *get_si_addr(void __user *addr, unsigned long sig, > + unsigned long si_code) > +{ > + if (current->sighand->action[sig - 1].sa.sa_flags & SA_EXPOSE_TAGBITS) > + return addr; > + > + return arch_untagged_si_addr(addr, sig, si_code); > +} > + > int force_sig_fault_to_task(int sig, int code, void __user *addr > ___ARCH_SI_TRAPNO(int trapno) > ___ARCH_SI_IA64(int imm, unsigned int flags, unsigned long isr) > @@ -1661,7 +1670,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr > info.si_signo = sig; > info.si_errno = 0; > info.si_code = code; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, sig, code); > #ifdef __ARCH_SI_TRAPNO > info.si_trapno = trapno; > #endif > @@ -1693,7 +1702,7 @@ int send_sig_fault(int sig, int code, void __user *addr > info.si_signo = sig; > info.si_errno = 0; > info.si_code = code; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, sig, code); > #ifdef __ARCH_SI_TRAPNO > info.si_trapno = trapno; > #endif > @@ -1714,7 +1723,7 @@ int force_sig_mceerr(int code, void __user *addr, short lsb) > info.si_signo = SIGBUS; > info.si_errno = 0; > info.si_code = code; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, SIGBUS, code); > info.si_addr_lsb = lsb; > return force_sig_info(&info); > } > @@ -1728,7 +1737,7 @@ int send_sig_mceerr(int code, void __user *addr, short lsb, struct task_struct * > info.si_signo = SIGBUS; > info.si_errno = 0; > info.si_code = code; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, SIGBUS, code); > info.si_addr_lsb = lsb; > return send_sig_info(info.si_signo, &info, t); > } > @@ -1742,7 +1751,7 @@ int force_sig_bnderr(void __user *addr, void __user *lower, void __user *upper) > info.si_signo = SIGSEGV; > info.si_errno = 0; > info.si_code = SEGV_BNDERR; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, SIGSEGV, SEGV_BNDERR); > info.si_lower = lower; > info.si_upper = upper; > return force_sig_info(&info); > @@ -1757,7 +1766,7 @@ int force_sig_pkuerr(void __user *addr, u32 pkey) > info.si_signo = SIGSEGV; > info.si_errno = 0; > info.si_code = SEGV_PKUERR; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, SIGSEGV, SEGV_PKUERR); > info.si_pkey = pkey; > return force_sig_info(&info); > } > @@ -1774,7 +1783,7 @@ int force_sig_ptrace_errno_trap(int errno, void __user *addr) > info.si_signo = SIGTRAP; > info.si_errno = errno; > info.si_code = TRAP_HWBKPT; > - info.si_addr = addr; > + info.si_addr = get_si_addr(addr, SIGTRAP, TRAP_HWBKPT); > return force_sig_info(&info); > }
On Sun, Nov 15, 2020 at 08:08:36AM -0600, Eric W. Biederman wrote: > Peter Collingbourne <pcc@google.com> writes: > > > The kernel currently clears the tag bits (i.e. bits 56-63) in the fault > > address exposed via siginfo.si_addr and sigcontext.fault_address. However, > > the tag bits may be needed by tools in order to accurately diagnose > > memory errors, such as HWASan [1] or future tools based on the Memory > > Tagging Extension (MTE). > > > > We should not stop clearing these bits in the existing fault address > > fields, because there may be existing userspace applications that are > > expecting the tag bits to be cleared. Instead, introduce a flag in > > sigaction.sa_flags, SA_EXPOSE_TAGBITS, and only expose the tag bits > > there if the signal handler has this flag set. > > For future architectures that implement something similar does it make > sense that to hide tag bits by default? I think on arm64 this comes from the fact that the tag bits information is not available in all scenarios. To keep things clean, the decision was taken early on to just zero them all the time in si_addr to avoid software getting confused. Possibly other arches do something similar, but that would need digging into. There seems to be debate on whether these bits are part of the address or not. For si_addr I think they probably _should_ be regarded as part of the address in general, and arches that can always report all these bits in si_addr should probably do so IMHO. > I am wondering if SA_EXPOSE_TABGITS might make sense as an architecture > specific sa bit. Perhaps. Peter, do you see other arches masking out bits in si_addr? [...] Cheers ---Dave
On Mon, Nov 16, 2020 at 5:36 AM Dave Martin <Dave.Martin@arm.com> wrote: > > On Sun, Nov 15, 2020 at 08:08:36AM -0600, Eric W. Biederman wrote: > > Peter Collingbourne <pcc@google.com> writes: > > > > > The kernel currently clears the tag bits (i.e. bits 56-63) in the fault > > > address exposed via siginfo.si_addr and sigcontext.fault_address. However, > > > the tag bits may be needed by tools in order to accurately diagnose > > > memory errors, such as HWASan [1] or future tools based on the Memory > > > Tagging Extension (MTE). > > > > > > We should not stop clearing these bits in the existing fault address > > > fields, because there may be existing userspace applications that are > > > expecting the tag bits to be cleared. Instead, introduce a flag in > > > sigaction.sa_flags, SA_EXPOSE_TAGBITS, and only expose the tag bits > > > there if the signal handler has this flag set. > > > > For future architectures that implement something similar does it make > > sense that to hide tag bits by default? > > I think on arm64 this comes from the fact that the tag bits information > is not available in all scenarios. To keep things clean, the decision > was taken early on to just zero them all the time in si_addr to avoid > software getting confused. Possibly other arches do something similar, > but that would need digging into. > > There seems to be debate on whether these bits are part of the address > or not. For si_addr I think they probably _should_ be regarded as part > of the address in general, and arches that can always report all these > bits in si_addr should probably do so IMHO. > > > I am wondering if SA_EXPOSE_TABGITS might make sense as an architecture > > specific sa bit. > > Perhaps. Peter, do you see other arches masking out bits in si_addr? I think it's possible, since it seems likely to me that the bits would only be able to be exposed unconditionally if the architecture with the tag bits is new. For existing architectures that are being extended with tag bits (e.g. RISC-V), I can see folks running into the same problem of software getting confused by the tag bits, so they would want to put them behind a flag, ideally the same one. Another point in favor of making it generic is that in many cases where you want these bits your signal handler will for the most part not be arch-specific. In Android's case for example we have a tombstone signal handler which is mostly generic with the arch-specific parts hidden behind an abstraction, and the libsigchain signal handler that needs to hide the bits if the flag is not set, but is otherwise generic. Making it generic avoids an #ifdef around the points where we need to refer to the flag. Please see my AOSP userspace changes [1] for reference. As you can see there is no #ifdef __aarch64__ required at all except for tests (there is already a helper function for untagging addresses that has the required #ifdef), but there are several points at which we need to refer to the flag. With an arch-specific flag the #ifdef would become more pervasive. Peter [1] https://android-review.googlesource.com/id/I57f24c07c01ceb3e5b81cfc15edf559ef7dfc740
On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: > diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > index eab4323609b9..19d284b70384 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -53,12 +53,25 @@ visibility. > Preserving tags > --------------- > > -Non-zero tags are not preserved when delivering signals. This means that > -signal handlers in applications making use of tags cannot rely on the > -tag information for user virtual addresses being maintained for fields > -inside siginfo_t. One exception to this rule is for signals raised in > -response to watchpoint debug exceptions, where the tag information will > -be preserved. > +When delivering signals, non-zero tags are not preserved in > +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > +sigaction.sa_flags when the signal handler was installed. This means > +that signal handlers in applications making use of tags cannot rely > +on the tag information for user virtual addresses being maintained > +in these fields unless the flag was set. > + > +Due to architecture limitations, bits 63:60 of the fault address > +are not preserved in response to synchronous tag check faults > +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > +treat the values of these bits as undefined in order to accommodate > +future architecture revisions which may preserve the bits. If future architecture versions will preserve these bits, most likely we'll add a new HWCAP bit so that the user knows what's going on. But the user shouldn't rely on them being 0, just in case. > +For signals raised in response to watchpoint debug exceptions, the > +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > +flag setting. > + > +Non-zero tags are never preserved in sigcontext.fault_address > +regardless of the SA_EXPOSE_TAGBITS flag setting. We could've done it the other way around (fault_address tagged, si_addr untagged) but that would be specific to arm64, so I think we should solve it for other architectures that implement (or plan to) tagging. The fault_address in the arm64 sigcontext was an oversight, we should have removed it but when we realised it was already ABI. Anyway, I'm fine with the arm64 changes here: Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> With Eric's ack, I'm happy to take the series through the arm64 tree, otherwise Eric's tree is fine as well. Thanks.
Catalin Marinas <catalin.marinas@arm.com> writes: > On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: >> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst >> index eab4323609b9..19d284b70384 100644 >> --- a/Documentation/arm64/tagged-pointers.rst >> +++ b/Documentation/arm64/tagged-pointers.rst >> @@ -53,12 +53,25 @@ visibility. >> Preserving tags >> --------------- >> >> -Non-zero tags are not preserved when delivering signals. This means that >> -signal handlers in applications making use of tags cannot rely on the >> -tag information for user virtual addresses being maintained for fields >> -inside siginfo_t. One exception to this rule is for signals raised in >> -response to watchpoint debug exceptions, where the tag information will >> -be preserved. >> +When delivering signals, non-zero tags are not preserved in >> +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in >> +sigaction.sa_flags when the signal handler was installed. This means >> +that signal handlers in applications making use of tags cannot rely >> +on the tag information for user virtual addresses being maintained >> +in these fields unless the flag was set. >> + >> +Due to architecture limitations, bits 63:60 of the fault address >> +are not preserved in response to synchronous tag check faults >> +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should >> +treat the values of these bits as undefined in order to accommodate >> +future architecture revisions which may preserve the bits. > > If future architecture versions will preserve these bits, most likely > we'll add a new HWCAP bit so that the user knows what's going on. But > the user shouldn't rely on them being 0, just in case. > >> +For signals raised in response to watchpoint debug exceptions, the >> +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS >> +flag setting. >> + >> +Non-zero tags are never preserved in sigcontext.fault_address >> +regardless of the SA_EXPOSE_TAGBITS flag setting. > > We could've done it the other way around (fault_address tagged, si_addr > untagged) but that would be specific to arm64, so I think we should > solve it for other architectures that implement (or plan to) tagging. > The fault_address in the arm64 sigcontext was an oversight, we should > have removed it but when we realised it was already ABI. > > Anyway, I'm fine with the arm64 changes here: > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > > With Eric's ack, I'm happy to take the series through the arm64 tree, > otherwise Eric's tree is fine as well. In general I am fine with the last two patches. I want to understand where the value for SA_UNSUPPORTED comes from, and while I have good answers I am still digesting the question of if SA_EXPOSE_TAGBITS should be implemented in the arch specific header or in a generic header. I quite agree it should have a generic definition/implementation. I just don't know if it makes sense to make the value available to userspace if the architecture does not have tagbits. Mostly my concern is about bit consumption as we only have 30ish sigaction bits. I will follow with my acks when I have resolved those issues. Thank you, Eric
On Mon, Nov 16, 2020 at 03:55:05PM -0600, Eric W. Biederman wrote: > Catalin Marinas <catalin.marinas@arm.com> writes: > > On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: > >> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > >> index eab4323609b9..19d284b70384 100644 > >> --- a/Documentation/arm64/tagged-pointers.rst > >> +++ b/Documentation/arm64/tagged-pointers.rst > >> @@ -53,12 +53,25 @@ visibility. > >> Preserving tags > >> --------------- > >> > >> -Non-zero tags are not preserved when delivering signals. This means that > >> -signal handlers in applications making use of tags cannot rely on the > >> -tag information for user virtual addresses being maintained for fields > >> -inside siginfo_t. One exception to this rule is for signals raised in > >> -response to watchpoint debug exceptions, where the tag information will > >> -be preserved. > >> +When delivering signals, non-zero tags are not preserved in > >> +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > >> +sigaction.sa_flags when the signal handler was installed. This means > >> +that signal handlers in applications making use of tags cannot rely > >> +on the tag information for user virtual addresses being maintained > >> +in these fields unless the flag was set. > >> + > >> +Due to architecture limitations, bits 63:60 of the fault address > >> +are not preserved in response to synchronous tag check faults > >> +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > >> +treat the values of these bits as undefined in order to accommodate > >> +future architecture revisions which may preserve the bits. > > > > If future architecture versions will preserve these bits, most likely > > we'll add a new HWCAP bit so that the user knows what's going on. But > > the user shouldn't rely on them being 0, just in case. > > > >> +For signals raised in response to watchpoint debug exceptions, the > >> +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > >> +flag setting. > >> + > >> +Non-zero tags are never preserved in sigcontext.fault_address > >> +regardless of the SA_EXPOSE_TAGBITS flag setting. > > > > We could've done it the other way around (fault_address tagged, si_addr > > untagged) but that would be specific to arm64, so I think we should > > solve it for other architectures that implement (or plan to) tagging. > > The fault_address in the arm64 sigcontext was an oversight, we should > > have removed it but when we realised it was already ABI. > > > > Anyway, I'm fine with the arm64 changes here: > > > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > > > > With Eric's ack, I'm happy to take the series through the arm64 tree, > > otherwise Eric's tree is fine as well. > > In general I am fine with the last two patches. > > I want to understand where the value for SA_UNSUPPORTED comes from, and > while I have good answers I am still digesting the question of if > SA_EXPOSE_TAGBITS should be implemented in the arch specific header or > in a generic header. I quite agree it should have a generic > definition/implementation. I just don't know if it makes sense to make > the value available to userspace if the architecture does not have > tagbits. Mostly my concern is about bit consumption as we only have > 30ish sigaction bits. An alternative would be to make this opt-in per process (or thread) based on a prctl() call. We already have one for PR_TAGGED_ADDR_ENABLE to allow tagged addresses from user at the syscall ABI level. Another bit in there would allow si_addr to be tagged. The disadvantage is that this is quite coarse control affecting other signal handlers. > I will follow with my acks when I have resolved those issues. Thanks.
On Mon, Nov 16, 2020 at 1:55 PM Eric W. Biederman <ebiederm@xmission.com> wrote: > > Catalin Marinas <catalin.marinas@arm.com> writes: > > > On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: > >> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > >> index eab4323609b9..19d284b70384 100644 > >> --- a/Documentation/arm64/tagged-pointers.rst > >> +++ b/Documentation/arm64/tagged-pointers.rst > >> @@ -53,12 +53,25 @@ visibility. > >> Preserving tags > >> --------------- > >> > >> -Non-zero tags are not preserved when delivering signals. This means that > >> -signal handlers in applications making use of tags cannot rely on the > >> -tag information for user virtual addresses being maintained for fields > >> -inside siginfo_t. One exception to this rule is for signals raised in > >> -response to watchpoint debug exceptions, where the tag information will > >> -be preserved. > >> +When delivering signals, non-zero tags are not preserved in > >> +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > >> +sigaction.sa_flags when the signal handler was installed. This means > >> +that signal handlers in applications making use of tags cannot rely > >> +on the tag information for user virtual addresses being maintained > >> +in these fields unless the flag was set. > >> + > >> +Due to architecture limitations, bits 63:60 of the fault address > >> +are not preserved in response to synchronous tag check faults > >> +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > >> +treat the values of these bits as undefined in order to accommodate > >> +future architecture revisions which may preserve the bits. > > > > If future architecture versions will preserve these bits, most likely > > we'll add a new HWCAP bit so that the user knows what's going on. But > > the user shouldn't rely on them being 0, just in case. > > > >> +For signals raised in response to watchpoint debug exceptions, the > >> +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > >> +flag setting. > >> + > >> +Non-zero tags are never preserved in sigcontext.fault_address > >> +regardless of the SA_EXPOSE_TAGBITS flag setting. > > > > We could've done it the other way around (fault_address tagged, si_addr > > untagged) but that would be specific to arm64, so I think we should > > solve it for other architectures that implement (or plan to) tagging. > > The fault_address in the arm64 sigcontext was an oversight, we should > > have removed it but when we realised it was already ABI. > > > > Anyway, I'm fine with the arm64 changes here: > > > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > > > > With Eric's ack, I'm happy to take the series through the arm64 tree, > > otherwise Eric's tree is fine as well. > > In general I am fine with the last two patches. > > I want to understand where the value for SA_UNSUPPORTED comes from, and I hope I explained it well enough in [1]. If documenting the arch-specific bits that way looks good to you let me know and I will update patch 3. > while I have good answers I am still digesting the question of if > SA_EXPOSE_TAGBITS should be implemented in the arch specific header or > in a generic header. I quite agree it should have a generic > definition/implementation. I just don't know if it makes sense to make > the value available to userspace if the architecture does not have > tagbits. Mostly my concern is about bit consumption as we only have > 30ish sigaction bits. As mentioned in [2] I would favor making the bits generic as that would simplify the client code. And I would personally not be too concerned about consuming bits here. Our historical rate of adding new bits is very low (as far as I know these are the first new bits to be added in about 20 years!) And once we are at the point where we are close to running out of bits it would be a good time to consider a new sigaction API anyway that addresses some of the historical warts of the existing one, and at that point we should be able to come up with a way to add more bits. Peter [1] https://lore.kernel.org/linux-arm-kernel/CAMn1gO52j4fSEn5S2GdrtyCq+iiaMK16DkKiyj=Go91Jy+xR-w@mail.gmail.com/ [2] https://lore.kernel.org/linux-arm-kernel/CAMn1gO6n7NrM8A+vkMt=ixvbSzUJbrr2s6Ko3WENPoT-84J15w@mail.gmail.com/
Peter Collingbourne <pcc@google.com> writes: > On Mon, Nov 16, 2020 at 1:55 PM Eric W. Biederman <ebiederm@xmission.com> wrote: >> >> Catalin Marinas <catalin.marinas@arm.com> writes: >> >> > On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: >> >> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst >> >> index eab4323609b9..19d284b70384 100644 >> >> --- a/Documentation/arm64/tagged-pointers.rst >> >> +++ b/Documentation/arm64/tagged-pointers.rst >> >> @@ -53,12 +53,25 @@ visibility. >> >> Preserving tags >> >> --------------- >> >> >> >> -Non-zero tags are not preserved when delivering signals. This means that >> >> -signal handlers in applications making use of tags cannot rely on the >> >> -tag information for user virtual addresses being maintained for fields >> >> -inside siginfo_t. One exception to this rule is for signals raised in >> >> -response to watchpoint debug exceptions, where the tag information will >> >> -be preserved. >> >> +When delivering signals, non-zero tags are not preserved in >> >> +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in >> >> +sigaction.sa_flags when the signal handler was installed. This means >> >> +that signal handlers in applications making use of tags cannot rely >> >> +on the tag information for user virtual addresses being maintained >> >> +in these fields unless the flag was set. >> >> + >> >> +Due to architecture limitations, bits 63:60 of the fault address >> >> +are not preserved in response to synchronous tag check faults >> >> +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should >> >> +treat the values of these bits as undefined in order to accommodate >> >> +future architecture revisions which may preserve the bits. >> > >> > If future architecture versions will preserve these bits, most likely >> > we'll add a new HWCAP bit so that the user knows what's going on. But >> > the user shouldn't rely on them being 0, just in case. >> > >> >> +For signals raised in response to watchpoint debug exceptions, the >> >> +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS >> >> +flag setting. >> >> + >> >> +Non-zero tags are never preserved in sigcontext.fault_address >> >> +regardless of the SA_EXPOSE_TAGBITS flag setting. >> > >> > We could've done it the other way around (fault_address tagged, si_addr >> > untagged) but that would be specific to arm64, so I think we should >> > solve it for other architectures that implement (or plan to) tagging. >> > The fault_address in the arm64 sigcontext was an oversight, we should >> > have removed it but when we realised it was already ABI. >> > >> > Anyway, I'm fine with the arm64 changes here: >> > >> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> >> > >> > With Eric's ack, I'm happy to take the series through the arm64 tree, >> > otherwise Eric's tree is fine as well. >> >> In general I am fine with the last two patches. >> >> I want to understand where the value for SA_UNSUPPORTED comes from, and > > I hope I explained it well enough in [1]. If documenting the > arch-specific bits that way looks good to you let me know and I will > update patch 3. Bah. I missed your reply. Please send me an incremental patch against: https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git signal-for-v5.11 As I have already applied your first 4 patches and have them in linux-next. >> while I have good answers I am still digesting the question of if >> SA_EXPOSE_TAGBITS should be implemented in the arch specific header or >> in a generic header. I quite agree it should have a generic >> definition/implementation. I just don't know if it makes sense to make >> the value available to userspace if the architecture does not have >> tagbits. Mostly my concern is about bit consumption as we only have >> 30ish sigaction bits. > > As mentioned in [2] I would favor making the bits generic as that > would simplify the client code. And I would personally not be too > concerned about consuming bits here. Our historical rate of adding new > bits is very low (as far as I know these are the first new bits to be > added in about 20 years!) And once we are at the point where we are > close to running out of bits it would be a good time to consider a new > sigaction API anyway that addresses some of the historical warts of > the existing one, and at that point we should be able to come up with > a way to add more bits. It is a good point that this areay hasn't seen much action in ages. So there is not too much need to be concerned. In general portable code will need to do "#ifdef SA_EXPOSE_TAGBITS" somewhere. But certainly it should be at least as generic as SA_RESTORER. With the same meaning everywhere it is defined. And certainly it makes sense for the implementation to live in the generic signal code for to ensure all architectures implement it with the same semantics. I am going to sleep on this one and then see if I see any real concerns. This is bike-shedding I know, and you have done a very nice job gettin this far. So I don't expect I will come up with any compelling reasons to change after sleeping on it, but I am going to sleep on it. > [1] https://lore.kernel.org/linux-arm-kernel/CAMn1gO52j4fSEn5S2GdrtyCq+iiaMK16DkKiyj=Go91Jy+xR-w@mail.gmail.com/ > [2] https://lore.kernel.org/linux-arm-kernel/CAMn1gO6n7NrM8A+vkMt=ixvbSzUJbrr2s6Ko3WENPoT-84J15w@mail.gmail.com/ Eric
On Mon, Nov 16, 2020 at 4:00 PM Eric W. Biederman <ebiederm@xmission.com> wrote: > > Peter Collingbourne <pcc@google.com> writes: > > > On Mon, Nov 16, 2020 at 1:55 PM Eric W. Biederman <ebiederm@xmission.com> wrote: > >> > >> Catalin Marinas <catalin.marinas@arm.com> writes: > >> > >> > On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: > >> >> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > >> >> index eab4323609b9..19d284b70384 100644 > >> >> --- a/Documentation/arm64/tagged-pointers.rst > >> >> +++ b/Documentation/arm64/tagged-pointers.rst > >> >> @@ -53,12 +53,25 @@ visibility. > >> >> Preserving tags > >> >> --------------- > >> >> > >> >> -Non-zero tags are not preserved when delivering signals. This means that > >> >> -signal handlers in applications making use of tags cannot rely on the > >> >> -tag information for user virtual addresses being maintained for fields > >> >> -inside siginfo_t. One exception to this rule is for signals raised in > >> >> -response to watchpoint debug exceptions, where the tag information will > >> >> -be preserved. > >> >> +When delivering signals, non-zero tags are not preserved in > >> >> +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > >> >> +sigaction.sa_flags when the signal handler was installed. This means > >> >> +that signal handlers in applications making use of tags cannot rely > >> >> +on the tag information for user virtual addresses being maintained > >> >> +in these fields unless the flag was set. > >> >> + > >> >> +Due to architecture limitations, bits 63:60 of the fault address > >> >> +are not preserved in response to synchronous tag check faults > >> >> +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > >> >> +treat the values of these bits as undefined in order to accommodate > >> >> +future architecture revisions which may preserve the bits. > >> > > >> > If future architecture versions will preserve these bits, most likely > >> > we'll add a new HWCAP bit so that the user knows what's going on. But > >> > the user shouldn't rely on them being 0, just in case. > >> > > >> >> +For signals raised in response to watchpoint debug exceptions, the > >> >> +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > >> >> +flag setting. > >> >> + > >> >> +Non-zero tags are never preserved in sigcontext.fault_address > >> >> +regardless of the SA_EXPOSE_TAGBITS flag setting. > >> > > >> > We could've done it the other way around (fault_address tagged, si_addr > >> > untagged) but that would be specific to arm64, so I think we should > >> > solve it for other architectures that implement (or plan to) tagging. > >> > The fault_address in the arm64 sigcontext was an oversight, we should > >> > have removed it but when we realised it was already ABI. > >> > > >> > Anyway, I'm fine with the arm64 changes here: > >> > > >> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > >> > > >> > With Eric's ack, I'm happy to take the series through the arm64 tree, > >> > otherwise Eric's tree is fine as well. > >> > >> In general I am fine with the last two patches. > >> > >> I want to understand where the value for SA_UNSUPPORTED comes from, and > > > > I hope I explained it well enough in [1]. If documenting the > > arch-specific bits that way looks good to you let me know and I will > > update patch 3. > > Bah. I missed your reply. > > Please send me an incremental patch against: > > https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git signal-for-v5.11 > > As I have already applied your first 4 patches and have them in > linux-next. Okay, I've sent a v17 to be applied on top of your branch. > >> while I have good answers I am still digesting the question of if > >> SA_EXPOSE_TAGBITS should be implemented in the arch specific header or > >> in a generic header. I quite agree it should have a generic > >> definition/implementation. I just don't know if it makes sense to make > >> the value available to userspace if the architecture does not have > >> tagbits. Mostly my concern is about bit consumption as we only have > >> 30ish sigaction bits. > > > > As mentioned in [2] I would favor making the bits generic as that > > would simplify the client code. And I would personally not be too > > concerned about consuming bits here. Our historical rate of adding new > > bits is very low (as far as I know these are the first new bits to be > > added in about 20 years!) And once we are at the point where we are > > close to running out of bits it would be a good time to consider a new > > sigaction API anyway that addresses some of the historical warts of > > the existing one, and at that point we should be able to come up with > > a way to add more bits. > > It is a good point that this areay hasn't seen much action in ages. So > there is not too much need to be concerned. > > In general portable code will need to do "#ifdef SA_EXPOSE_TAGBITS" > somewhere. But certainly it should be at least as generic as Sure. It's worth noting though that if you know that you are targeting Linux and have the latest kernel headers (which is the case for Android platform code for example) you would be able to use new #defines unconditionally. > SA_RESTORER. With the same meaning everywhere it is defined. > And certainly it makes sense for the implementation to live > in the generic signal code for to ensure all architectures implement > it with the same semantics. > > I am going to sleep on this one and then see if I see any real concerns. > > This is bike-shedding I know, and you have done a very nice job gettin > this far. So I don't expect I will come up with any compelling reasons > to change after sleeping on it, but I am going to sleep on it. Okay, let me know if you find any concerns. Peter
diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst index eab4323609b9..19d284b70384 100644 --- a/Documentation/arm64/tagged-pointers.rst +++ b/Documentation/arm64/tagged-pointers.rst @@ -53,12 +53,25 @@ visibility. Preserving tags --------------- -Non-zero tags are not preserved when delivering signals. This means that -signal handlers in applications making use of tags cannot rely on the -tag information for user virtual addresses being maintained for fields -inside siginfo_t. One exception to this rule is for signals raised in -response to watchpoint debug exceptions, where the tag information will -be preserved. +When delivering signals, non-zero tags are not preserved in +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in +sigaction.sa_flags when the signal handler was installed. This means +that signal handlers in applications making use of tags cannot rely +on the tag information for user virtual addresses being maintained +in these fields unless the flag was set. + +Due to architecture limitations, bits 63:60 of the fault address +are not preserved in response to synchronous tag check faults +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should +treat the values of these bits as undefined in order to accommodate +future architecture revisions which may preserve the bits. + +For signals raised in response to watchpoint debug exceptions, the +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS +flag setting. + +Non-zero tags are never preserved in sigcontext.fault_address +regardless of the SA_EXPOSE_TAGBITS flag setting. The architecture prevents the use of a tagged PC, so the upper byte will be set to a sign-extension of bit 55 on exception return. diff --git a/arch/arm64/include/asm/exception.h b/arch/arm64/include/asm/exception.h index 99b9383cd036..2a8aa1884d8a 100644 --- a/arch/arm64/include/asm/exception.h +++ b/arch/arm64/include/asm/exception.h @@ -32,7 +32,7 @@ static inline u32 disr_to_esr(u64 disr) } asmlinkage void enter_from_user_mode(void); -void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs); +void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs); void do_undefinstr(struct pt_regs *regs); void do_bti(struct pt_regs *regs); asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr); diff --git a/arch/arm64/include/asm/signal.h b/arch/arm64/include/asm/signal.h new file mode 100644 index 000000000000..ef449f5f4ba8 --- /dev/null +++ b/arch/arm64/include/asm/signal.h @@ -0,0 +1,25 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ARM64_ASM_SIGNAL_H +#define __ARM64_ASM_SIGNAL_H + +#include <asm/memory.h> +#include <uapi/asm/signal.h> +#include <uapi/asm/siginfo.h> + +static inline void __user *arch_untagged_si_addr(void __user *addr, + unsigned long sig, + unsigned long si_code) +{ + /* + * For historical reasons, all bits of the fault address are exposed as + * address bits for watchpoint exceptions. New architectures should + * handle the tag bits consistently. + */ + if (sig == SIGTRAP && si_code == TRAP_BRKPT) + return addr; + + return untagged_addr(addr); +} +#define arch_untagged_si_addr arch_untagged_si_addr + +#endif diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h index 1ab63cfbbaf1..673be2d1263c 100644 --- a/arch/arm64/include/asm/system_misc.h +++ b/arch/arm64/include/asm/system_misc.h @@ -22,7 +22,7 @@ void die(const char *msg, struct pt_regs *regs, int err); struct siginfo; void arm64_notify_die(const char *str, struct pt_regs *regs, - int signo, int sicode, void __user *addr, + int signo, int sicode, unsigned long far, int err); void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned int, diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h index d96dc2c7c09d..54f32a0675df 100644 --- a/arch/arm64/include/asm/traps.h +++ b/arch/arm64/include/asm/traps.h @@ -26,9 +26,9 @@ void register_undef_hook(struct undef_hook *hook); void unregister_undef_hook(struct undef_hook *hook); void force_signal_inject(int signal, int code, unsigned long address, unsigned int err); void arm64_notify_segfault(unsigned long addr); -void arm64_force_sig_fault(int signo, int code, void __user *addr, const char *str); -void arm64_force_sig_mceerr(int code, void __user *addr, short lsb, const char *str); -void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr, const char *str); +void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str); +void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str); +void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str); /* * Move regs->pc to next instruction and do necessary setup before it diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index fa76151de6ff..4f3661eeb7ec 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -234,9 +234,8 @@ static void send_user_sigtrap(int si_code) if (interrupts_enabled(regs)) local_irq_enable(); - arm64_force_sig_fault(SIGTRAP, si_code, - (void __user *)instruction_pointer(regs), - "User debug trap"); + arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs), + "User debug trap"); } static int single_step_handler(unsigned long unused, unsigned int esr, diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 43d4c329775f..dbbddfbf4a72 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -22,7 +22,6 @@ static void notrace el1_abort(struct pt_regs *regs, unsigned long esr) unsigned long far = read_sysreg(far_el1); local_daif_inherit(regs); - far = untagged_addr(far); do_mem_abort(far, esr, regs); } NOKPROBE_SYMBOL(el1_abort); @@ -114,7 +113,6 @@ static void notrace el0_da(struct pt_regs *regs, unsigned long esr) user_exit_irqoff(); local_daif_restore(DAIF_PROCCTX); - far = untagged_addr(far); do_mem_abort(far, esr, regs); } NOKPROBE_SYMBOL(el0_da); diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index f49b349e16a3..8ac487c84e37 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -192,14 +192,11 @@ static void ptrace_hbptriggered(struct perf_event *bp, break; } } - arm64_force_sig_ptrace_errno_trap(si_errno, - (void __user *)bkpt->trigger, + arm64_force_sig_ptrace_errno_trap(si_errno, bkpt->trigger, desc); } #endif - arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, - (void __user *)(bkpt->trigger), - desc); + arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, bkpt->trigger, desc); } /* diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c index 3c18c2454089..265fe3eb1069 100644 --- a/arch/arm64/kernel/sys_compat.c +++ b/arch/arm64/kernel/sys_compat.c @@ -68,7 +68,7 @@ do_compat_cache_op(unsigned long start, unsigned long end, int flags) */ long compat_arm_syscall(struct pt_regs *regs, int scno) { - void __user *addr; + unsigned long addr; switch (scno) { /* @@ -111,8 +111,7 @@ long compat_arm_syscall(struct pt_regs *regs, int scno) break; } - addr = (void __user *)instruction_pointer(regs) - - (compat_thumb_mode(regs) ? 2 : 4); + addr = instruction_pointer(regs) - (compat_thumb_mode(regs) ? 2 : 4); arm64_notify_die("Oops - bad compat syscall(2)", regs, SIGILL, ILL_ILLTRP, addr, scno); diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index 8af4e0e85736..f4ddbe9ed3f1 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -170,32 +170,32 @@ static void arm64_show_signal(int signo, const char *str) __show_regs(regs); } -void arm64_force_sig_fault(int signo, int code, void __user *addr, +void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str) { arm64_show_signal(signo, str); if (signo == SIGKILL) force_sig(SIGKILL); else - force_sig_fault(signo, code, addr); + force_sig_fault(signo, code, (void __user *)far); } -void arm64_force_sig_mceerr(int code, void __user *addr, short lsb, +void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str) { arm64_show_signal(SIGBUS, str); - force_sig_mceerr(code, addr, lsb); + force_sig_mceerr(code, (void __user *)far, lsb); } -void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr, +void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str) { arm64_show_signal(SIGTRAP, str); - force_sig_ptrace_errno_trap(errno, addr); + force_sig_ptrace_errno_trap(errno, (void __user *)far); } void arm64_notify_die(const char *str, struct pt_regs *regs, - int signo, int sicode, void __user *addr, + int signo, int sicode, unsigned long far, int err) { if (user_mode(regs)) { @@ -203,7 +203,7 @@ void arm64_notify_die(const char *str, struct pt_regs *regs, current->thread.fault_address = 0; current->thread.fault_code = err; - arm64_force_sig_fault(signo, sicode, addr, str); + arm64_force_sig_fault(signo, sicode, far, str); } else { die(str, regs, err); } @@ -374,7 +374,7 @@ void force_signal_inject(int signal, int code, unsigned long address, unsigned i signal = SIGKILL; } - arm64_notify_die(desc, regs, signal, code, (void __user *)address, err); + arm64_notify_die(desc, regs, signal, code, address, err); } /* @@ -385,7 +385,7 @@ void arm64_notify_segfault(unsigned long addr) int code; mmap_read_lock(current->mm); - if (find_vma(current->mm, addr) == NULL) + if (find_vma(current->mm, untagged_addr(addr)) == NULL) code = SEGV_MAPERR; else code = SEGV_ACCERR; @@ -448,12 +448,13 @@ NOKPROBE_SYMBOL(do_ptrauth_fault); static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs) { - unsigned long address; + unsigned long tagged_address, address; int rt = ESR_ELx_SYS64_ISS_RT(esr); int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT; int ret = 0; - address = untagged_addr(pt_regs_read_reg(regs, rt)); + tagged_address = pt_regs_read_reg(regs, rt); + address = untagged_addr(tagged_address); switch (crm) { case ESR_ELx_SYS64_ISS_CRM_DC_CVAU: /* DC CVAU, gets promoted */ @@ -480,7 +481,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs) } if (ret) - arm64_notify_segfault(address); + arm64_notify_segfault(tagged_address); else arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE); } @@ -772,7 +773,7 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr) */ void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr) { - void __user *pc = (void __user *)instruction_pointer(regs); + unsigned long pc = instruction_pointer(regs); current->thread.fault_address = 0; current->thread.fault_code = esr; diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 1ee94002801f..c5375cb7763d 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -40,7 +40,7 @@ #include <asm/traps.h> struct fault_info { - int (*fn)(unsigned long addr, unsigned int esr, + int (*fn)(unsigned long far, unsigned int esr, struct pt_regs *regs); int sig; int code; @@ -385,8 +385,11 @@ static void set_thread_esr(unsigned long address, unsigned int esr) current->thread.fault_code = esr; } -static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs) +static void do_bad_area(unsigned long far, unsigned int esr, + struct pt_regs *regs) { + unsigned long addr = untagged_addr(far); + /* * If we are in kernel mode at this point, we have no context to * handle this fault with. @@ -395,8 +398,7 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re const struct fault_info *inf = esr_to_fault_info(esr); set_thread_esr(addr, esr); - arm64_force_sig_fault(inf->sig, inf->code, (void __user *)addr, - inf->name); + arm64_force_sig_fault(inf->sig, inf->code, far, inf->name); } else { __do_kernel_fault(addr, esr, regs); } @@ -448,7 +450,7 @@ static bool is_write_abort(unsigned int esr) return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM); } -static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, +static int __kprobes do_page_fault(unsigned long far, unsigned int esr, struct pt_regs *regs) { const struct fault_info *inf; @@ -456,6 +458,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, vm_fault_t fault; unsigned long vm_flags = VM_ACCESS_FLAGS; unsigned int mm_flags = FAULT_FLAG_DEFAULT; + unsigned long addr = untagged_addr(far); if (kprobe_page_fault(regs, esr)) return 0; @@ -567,8 +570,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, * We had some memory, but were unable to successfully fix up * this page fault. */ - arm64_force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr, - inf->name); + arm64_force_sig_fault(SIGBUS, BUS_ADRERR, far, inf->name); } else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) { unsigned int lsb; @@ -576,8 +578,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, if (fault & VM_FAULT_HWPOISON_LARGE) lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); - arm64_force_sig_mceerr(BUS_MCEERR_AR, (void __user *)addr, lsb, - inf->name); + arm64_force_sig_mceerr(BUS_MCEERR_AR, far, lsb, inf->name); } else { /* * Something tried to access memory that isn't in our memory @@ -585,8 +586,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, */ arm64_force_sig_fault(SIGSEGV, fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR, - (void __user *)addr, - inf->name); + far, inf->name); } return 0; @@ -596,33 +596,35 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, return 0; } -static int __kprobes do_translation_fault(unsigned long addr, +static int __kprobes do_translation_fault(unsigned long far, unsigned int esr, struct pt_regs *regs) { + unsigned long addr = untagged_addr(far); + if (is_ttbr0_addr(addr)) - return do_page_fault(addr, esr, regs); + return do_page_fault(far, esr, regs); - do_bad_area(addr, esr, regs); + do_bad_area(far, esr, regs); return 0; } -static int do_alignment_fault(unsigned long addr, unsigned int esr, +static int do_alignment_fault(unsigned long far, unsigned int esr, struct pt_regs *regs) { - do_bad_area(addr, esr, regs); + do_bad_area(far, esr, regs); return 0; } -static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs) +static int do_bad(unsigned long far, unsigned int esr, struct pt_regs *regs) { return 1; /* "fault" */ } -static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) +static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs) { const struct fault_info *inf; - void __user *siaddr; + unsigned long siaddr; inf = esr_to_fault_info(esr); @@ -635,18 +637,23 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) } if (esr & ESR_ELx_FnV) - siaddr = NULL; + siaddr = 0; else - siaddr = (void __user *)addr; + siaddr = untagged_addr(far); arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr); return 0; } -static int do_tag_check_fault(unsigned long addr, unsigned int esr, +static int do_tag_check_fault(unsigned long far, unsigned int esr, struct pt_regs *regs) { - do_bad_area(addr, esr, regs); + /* + * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag + * check faults. Mask them out now so that userspace doesn't see them. + */ + far &= (1UL << 60) - 1; + do_bad_area(far, esr, regs); return 0; } @@ -717,11 +724,12 @@ static const struct fault_info fault_info[] = { { do_bad, SIGKILL, SI_KERNEL, "unknown 63" }, }; -void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) +void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs) { const struct fault_info *inf = esr_to_fault_info(esr); + unsigned long addr = untagged_addr(far); - if (!inf->fn(addr, esr, regs)) + if (!inf->fn(far, esr, regs)) return; if (!user_mode(regs)) { @@ -730,8 +738,7 @@ void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) show_pte(addr); } - arm64_notify_die(inf->name, regs, - inf->sig, inf->code, (void __user *)addr, esr); + arm64_notify_die(inf->name, regs, inf->sig, inf->code, addr, esr); } NOKPROBE_SYMBOL(do_mem_abort); @@ -744,8 +751,8 @@ NOKPROBE_SYMBOL(do_el0_irq_bp_hardening); void do_sp_pc_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs) { - arm64_notify_die("SP/PC alignment exception", regs, - SIGBUS, BUS_ADRALN, (void __user *)addr, esr); + arm64_notify_die("SP/PC alignment exception", regs, SIGBUS, BUS_ADRALN, + addr, esr); } NOKPROBE_SYMBOL(do_sp_pc_abort); @@ -871,8 +878,7 @@ void do_debug_exception(unsigned long addr_if_watchpoint, unsigned int esr, arm64_apply_bp_hardening(); if (inf->fn(addr_if_watchpoint, esr, regs)) { - arm64_notify_die(inf->name, regs, - inf->sig, inf->code, (void __user *)pc, esr); + arm64_notify_die(inf->name, regs, inf->sig, inf->code, pc, esr); } debug_exception_exit(regs); diff --git a/include/linux/signal.h b/include/linux/signal.h index b256f9c65661..205526c4003a 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -469,4 +469,18 @@ struct seq_file; extern void render_sigset_t(struct seq_file *, const char *, sigset_t *); #endif +#ifndef arch_untagged_si_addr +/* + * Given a fault address and a signal and si_code which correspond to the + * _sigfault union member, returns the address that must appear in si_addr if + * the signal handler does not have SA_EXPOSE_TAGBITS enabled in sa_flags. + */ +static inline void __user *arch_untagged_si_addr(void __user *addr, + unsigned long sig, + unsigned long si_code) +{ + return addr; +} +#endif + #endif /* _LINUX_SIGNAL_H */ diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h index a7887ad84d36..68e06c75c5b2 100644 --- a/include/linux/signal_types.h +++ b/include/linux/signal_types.h @@ -78,6 +78,6 @@ struct ksignal { #define UAPI_SA_FLAGS \ (SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART | \ - SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS) + SA_NODEFER | SA_RESETHAND | SA_EXPOSE_TAGBITS | __ARCH_UAPI_SA_FLAGS) #endif /* _LINUX_SIGNAL_TYPES_H */ diff --git a/include/uapi/asm-generic/signal-defs.h b/include/uapi/asm-generic/signal-defs.h index 0126ebda4d31..5276bdd4a9e2 100644 --- a/include/uapi/asm-generic/signal-defs.h +++ b/include/uapi/asm-generic/signal-defs.h @@ -20,6 +20,8 @@ * so this bit allows flag bit support to be detected from userspace while * allowing an old kernel to be distinguished from a kernel that supports every * flag bit. + * SA_EXPOSE_TAGBITS exposes an architecture-defined set of tag bits in + * siginfo.si_addr. * * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single * Unix names RESETHAND and NODEFER respectively. @@ -49,6 +51,7 @@ #define SA_RESETHAND 0x80000000 #endif #define SA_UNSUPPORTED 0x00000400 +#define SA_EXPOSE_TAGBITS 0x00000800 #define SA_NOMASK SA_NODEFER #define SA_ONESHOT SA_RESETHAND diff --git a/kernel/signal.c b/kernel/signal.c index 8f34819e80de..16be62e6d341 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1650,6 +1650,15 @@ void force_sigsegv(int sig) force_sig(SIGSEGV); } +static void __user *get_si_addr(void __user *addr, unsigned long sig, + unsigned long si_code) +{ + if (current->sighand->action[sig - 1].sa.sa_flags & SA_EXPOSE_TAGBITS) + return addr; + + return arch_untagged_si_addr(addr, sig, si_code); +} + int force_sig_fault_to_task(int sig, int code, void __user *addr ___ARCH_SI_TRAPNO(int trapno) ___ARCH_SI_IA64(int imm, unsigned int flags, unsigned long isr) @@ -1661,7 +1670,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr info.si_signo = sig; info.si_errno = 0; info.si_code = code; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, sig, code); #ifdef __ARCH_SI_TRAPNO info.si_trapno = trapno; #endif @@ -1693,7 +1702,7 @@ int send_sig_fault(int sig, int code, void __user *addr info.si_signo = sig; info.si_errno = 0; info.si_code = code; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, sig, code); #ifdef __ARCH_SI_TRAPNO info.si_trapno = trapno; #endif @@ -1714,7 +1723,7 @@ int force_sig_mceerr(int code, void __user *addr, short lsb) info.si_signo = SIGBUS; info.si_errno = 0; info.si_code = code; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, SIGBUS, code); info.si_addr_lsb = lsb; return force_sig_info(&info); } @@ -1728,7 +1737,7 @@ int send_sig_mceerr(int code, void __user *addr, short lsb, struct task_struct * info.si_signo = SIGBUS; info.si_errno = 0; info.si_code = code; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, SIGBUS, code); info.si_addr_lsb = lsb; return send_sig_info(info.si_signo, &info, t); } @@ -1742,7 +1751,7 @@ int force_sig_bnderr(void __user *addr, void __user *lower, void __user *upper) info.si_signo = SIGSEGV; info.si_errno = 0; info.si_code = SEGV_BNDERR; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, SIGSEGV, SEGV_BNDERR); info.si_lower = lower; info.si_upper = upper; return force_sig_info(&info); @@ -1757,7 +1766,7 @@ int force_sig_pkuerr(void __user *addr, u32 pkey) info.si_signo = SIGSEGV; info.si_errno = 0; info.si_code = SEGV_PKUERR; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, SIGSEGV, SEGV_PKUERR); info.si_pkey = pkey; return force_sig_info(&info); } @@ -1774,7 +1783,7 @@ int force_sig_ptrace_errno_trap(int errno, void __user *addr) info.si_signo = SIGTRAP; info.si_errno = errno; info.si_code = TRAP_HWBKPT; - info.si_addr = addr; + info.si_addr = get_si_addr(addr, SIGTRAP, TRAP_HWBKPT); return force_sig_info(&info); }
The kernel currently clears the tag bits (i.e. bits 56-63) in the fault address exposed via siginfo.si_addr and sigcontext.fault_address. However, the tag bits may be needed by tools in order to accurately diagnose memory errors, such as HWASan [1] or future tools based on the Memory Tagging Extension (MTE). We should not stop clearing these bits in the existing fault address fields, because there may be existing userspace applications that are expecting the tag bits to be cleared. Instead, introduce a flag in sigaction.sa_flags, SA_EXPOSE_TAGBITS, and only expose the tag bits there if the signal handler has this flag set. [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html Signed-off-by: Peter Collingbourne <pcc@google.com> Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 --- v16: - add missing file v15: - switched to the SA_EXPOSE_TAGBITS approach proposed by Eric - rebased to 5.10-rc3 v14: - fix an inaccuracy in the commit message - add some comments to arch_addr_tag_bits_mask v13: - renamed si_xflags to si_faultflags - rebased to 5.10-rc2 v12: - add new fields to signal_compat.c test cases - rebased to 5.10-rc1 - mask out bits 63:60 for tag check faults v11: - add a comment explaining what the arch hook should do - rename ignored bits to tag bits v10: - rename the flag to SIFAULTFLAG_ADDR_IGNORED_BITS - use an arch hook to specify which bits are ignored, instead of passing them explicitly - while refactoring for the arch hook, noticed that my previous patches missed a case involving cache maintenance instructions, so expose the tag bits for that signal as well v9: - make the ignored bits fields generic - add some new dependent patches that prepare us to store the field in such a way that userspace can detect their presence v8: - rebase onto 5.8rc2 v7: - switch to a new siginfo field instead of using sigcontext - merge the patch back into one since the other patches are now unnecessary v6: - move fault address and fault code into the kernel_siginfo data structure - split the patch in three since it was getting large and now has generic and arch-specific parts v5: - add padding to fault_addr_top_byte_context in order to ensure the correct size and preserve sp alignment v4: - expose only the tag bits in the context instead of the entire FAR_EL1 - remove mention of the new context from the sigcontext.__reserved[] note v3: - add documentation to tagged-pointers.rst - update comments in sigcontext.h v2: - revert changes to hw_breakpoint.c - rename set_thread_esr to set_thread_far_esr Documentation/arm64/tagged-pointers.rst | 25 ++++++--- arch/arm64/include/asm/exception.h | 2 +- arch/arm64/include/asm/signal.h | 25 +++++++++ arch/arm64/include/asm/system_misc.h | 2 +- arch/arm64/include/asm/traps.h | 6 +-- arch/arm64/kernel/debug-monitors.c | 5 +- arch/arm64/kernel/entry-common.c | 2 - arch/arm64/kernel/ptrace.c | 7 +-- arch/arm64/kernel/sys_compat.c | 5 +- arch/arm64/kernel/traps.c | 29 ++++++----- arch/arm64/mm/fault.c | 68 ++++++++++++++----------- include/linux/signal.h | 14 +++++ include/linux/signal_types.h | 2 +- include/uapi/asm-generic/signal-defs.h | 3 ++ kernel/signal.c | 23 ++++++--- 15 files changed, 141 insertions(+), 77 deletions(-) create mode 100644 arch/arm64/include/asm/signal.h