| Message ID | 2dec46a70da175478932d034ebe74d0b4f5133c4.1602892799.git.pcc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: expose FAR_EL1 tag bits in siginfo | expand |
On Fri, Oct 16, 2020 at 05:12:33PM -0700, Peter Collingbourne wrote: > 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, create a new pair of > union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 > there, together with a mask specifying which bits are valid. > > A flag is added to si_xflags to allow userspace to determine whether > the values in the fields are valid. > > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > Signed-off-by: Peter Collingbourne <pcc@google.com> > Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 > --- > 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 SIXFLAG_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 | 21 +++++--- > arch/arm64/include/asm/exception.h | 2 +- > arch/arm64/include/asm/signal.h | 19 +++++++ > 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 ++++++++++++++----------- > arch/x86/kernel/signal_compat.c | 9 +++- > include/linux/compat.h | 2 + > include/linux/signal.h | 16 ++++++ > include/uapi/asm-generic/siginfo.h | 10 ++++ > kernel/signal.c | 18 ++++++- > 16 files changed, 148 insertions(+), 73 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..032c09a876f4 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -53,12 +53,21 @@ 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. > +Non-zero tags are not preserved in the fault address fields > +siginfo.si_addr or sigcontext.fault_address 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 in these fields. One exception to this rule is for > +signals raised in response to watchpoint debug exceptions, where the > +tag information will be preserved. > + > +The fault address tag is preserved in the si_addr_tag_bits field > +of siginfo, which is set for signals raised in response to data aborts > +and instruction aborts. The si_addr_tag_bits_mask field indicates > +which bits of the field are valid. The validity of these fields is > +indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags, > +and the validity of si_xflags in turn is indicated by the kernel > +indicating support for the sigaction.sa_flags flag SA_XFLAGS. > > 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..46f9b3c61896 > --- /dev/null > +++ b/arch/arm64/include/asm/signal.h > @@ -0,0 +1,19 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef __ARM64_ASM_SIGNAL_H > +#define __ARM64_ASM_SIGNAL_H > + > +#include <uapi/asm/signal.h> > +#include <uapi/asm/siginfo.h> > + > +static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig, > + unsigned long si_code) > +{ > + if (sig == SIGTRAP && si_code == TRAP_BRKPT) > + return 0; > + if (sig == SIGSEGV && si_code == SEGV_MTESERR) > + return 0xfUL << 56; Should this be 0xffUL << 56? I thought MTE ignored bits 63:60, rather than requiring them to be 0? The whole tag byte may be relevant for debugging purposes, even if only some of the bits are checked in hardware. For consistency, I wonder whether it makes sense to expose the bits as tag bits for watchpoint execeptions, even if they are left un-cleared in si_addr for historical reasons. > + return 0xffUL << 56; > +} > +#define arch_addr_tag_bits_mask arch_addr_tag_bits_mask [...] Cheers ---Dave
On Mon, Nov 2, 2020 at 9:55 AM Dave Martin <Dave.Martin@arm.com> wrote: > > On Fri, Oct 16, 2020 at 05:12:33PM -0700, Peter Collingbourne wrote: > > 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, create a new pair of > > union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 > > there, together with a mask specifying which bits are valid. > > > > A flag is added to si_xflags to allow userspace to determine whether > > the values in the fields are valid. > > > > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > > > Signed-off-by: Peter Collingbourne <pcc@google.com> > > Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 > > --- > > 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 SIXFLAG_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 | 21 +++++--- > > arch/arm64/include/asm/exception.h | 2 +- > > arch/arm64/include/asm/signal.h | 19 +++++++ > > 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 ++++++++++++++----------- > > arch/x86/kernel/signal_compat.c | 9 +++- > > include/linux/compat.h | 2 + > > include/linux/signal.h | 16 ++++++ > > include/uapi/asm-generic/siginfo.h | 10 ++++ > > kernel/signal.c | 18 ++++++- > > 16 files changed, 148 insertions(+), 73 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..032c09a876f4 100644 > > --- a/Documentation/arm64/tagged-pointers.rst > > +++ b/Documentation/arm64/tagged-pointers.rst > > @@ -53,12 +53,21 @@ 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. > > +Non-zero tags are not preserved in the fault address fields > > +siginfo.si_addr or sigcontext.fault_address 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 in these fields. One exception to this rule is for > > +signals raised in response to watchpoint debug exceptions, where the > > +tag information will be preserved. > > + > > +The fault address tag is preserved in the si_addr_tag_bits field > > +of siginfo, which is set for signals raised in response to data aborts > > +and instruction aborts. The si_addr_tag_bits_mask field indicates > > +which bits of the field are valid. The validity of these fields is > > +indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags, > > +and the validity of si_xflags in turn is indicated by the kernel > > +indicating support for the sigaction.sa_flags flag SA_XFLAGS. > > > > 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..46f9b3c61896 > > --- /dev/null > > +++ b/arch/arm64/include/asm/signal.h > > @@ -0,0 +1,19 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +#ifndef __ARM64_ASM_SIGNAL_H > > +#define __ARM64_ASM_SIGNAL_H > > + > > +#include <uapi/asm/signal.h> > > +#include <uapi/asm/siginfo.h> > > + > > +static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig, > > + unsigned long si_code) > > +{ > > + if (sig == SIGTRAP && si_code == TRAP_BRKPT) > > + return 0; > > + if (sig == SIGSEGV && si_code == SEGV_MTESERR) > > + return 0xfUL << 56; > > Should this be 0xffUL << 56? > > I thought MTE ignored bits 63:60, rather than requiring them to be 0? Yes, but the architecture defines FAR_EL1[63:60] as UNKNOWN for tag check faults. As such the bits are masked out in do_tag_check_fault and excluded from the mask here to indicate that they are not present. > The whole tag byte may be relevant for debugging purposes, even if only > some of the bits are checked in hardware. Yes and that's why it's a bit of a shame that the bits were defined as UNKNOWN. We had an idea for how to improve error reports by using those bits to link tag check faults to previous allocations, which was precluded by the missing bits. Hopefully a future revision of the architecture will define these bits for tag check faults (at least optionally). If that ever happens and support for the architecture extension is detected we could stop masking the bits out in do_tag_check_fault and set si_addr_tag_bits_mask to 0xffUL << 56, which would let userspace know that the bits are now present. > For consistency, I wonder whether it makes sense to expose the bits as > tag bits for watchpoint execeptions, even if they are left un-cleared in > si_addr for historical reasons. I don't have a strong opinion on whether to do this or not, but it seems like a nice property that the bits are either defined in si_addr or in si_addr_tag_bits. I think we could leave the watchpoint exception on arm64 as "weird for historical reasons" and insist that any future architectures adopting tagged addresses handle the tag bits uniformly. Peter
On Mon, Nov 02, 2020 at 07:59:25PM -0800, Peter Collingbourne wrote: > On Mon, Nov 2, 2020 at 9:55 AM Dave Martin <Dave.Martin@arm.com> wrote: > > > > On Fri, Oct 16, 2020 at 05:12:33PM -0700, Peter Collingbourne wrote: > > > 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, create a new pair of > > > union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 > > > there, together with a mask specifying which bits are valid. > > > > > > A flag is added to si_xflags to allow userspace to determine whether > > > the values in the fields are valid. > > > > > > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > > > > > Signed-off-by: Peter Collingbourne <pcc@google.com> > > > Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 > > > --- > > > 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 SIXFLAG_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 | 21 +++++--- > > > arch/arm64/include/asm/exception.h | 2 +- > > > arch/arm64/include/asm/signal.h | 19 +++++++ > > > 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 ++++++++++++++----------- > > > arch/x86/kernel/signal_compat.c | 9 +++- > > > include/linux/compat.h | 2 + > > > include/linux/signal.h | 16 ++++++ > > > include/uapi/asm-generic/siginfo.h | 10 ++++ > > > kernel/signal.c | 18 ++++++- > > > 16 files changed, 148 insertions(+), 73 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..032c09a876f4 100644 > > > --- a/Documentation/arm64/tagged-pointers.rst > > > +++ b/Documentation/arm64/tagged-pointers.rst > > > @@ -53,12 +53,21 @@ 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. > > > +Non-zero tags are not preserved in the fault address fields > > > +siginfo.si_addr or sigcontext.fault_address 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 in these fields. One exception to this rule is for > > > +signals raised in response to watchpoint debug exceptions, where the > > > +tag information will be preserved. > > > + > > > +The fault address tag is preserved in the si_addr_tag_bits field > > > +of siginfo, which is set for signals raised in response to data aborts > > > +and instruction aborts. The si_addr_tag_bits_mask field indicates > > > +which bits of the field are valid. The validity of these fields is > > > +indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags, > > > +and the validity of si_xflags in turn is indicated by the kernel > > > +indicating support for the sigaction.sa_flags flag SA_XFLAGS. > > > > > > 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..46f9b3c61896 > > > --- /dev/null > > > +++ b/arch/arm64/include/asm/signal.h > > > @@ -0,0 +1,19 @@ > > > +/* SPDX-License-Identifier: GPL-2.0 */ > > > +#ifndef __ARM64_ASM_SIGNAL_H > > > +#define __ARM64_ASM_SIGNAL_H > > > + > > > +#include <uapi/asm/signal.h> > > > +#include <uapi/asm/siginfo.h> > > > + > > > +static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig, > > > + unsigned long si_code) > > > +{ > > > + if (sig == SIGTRAP && si_code == TRAP_BRKPT) > > > + return 0; > > > + if (sig == SIGSEGV && si_code == SEGV_MTESERR) > > > + return 0xfUL << 56; > > > > Should this be 0xffUL << 56? > > > > I thought MTE ignored bits 63:60, rather than requiring them to be 0? > > Yes, but the architecture defines FAR_EL1[63:60] as UNKNOWN for tag > check faults. As such the bits are masked out in do_tag_check_fault > and excluded from the mask here to indicate that they are not present. Ah, OK. I'd forgotten that. So long as these bits are also zeroed in si_addr, I guess that's fine. > > > The whole tag byte may be relevant for debugging purposes, even if only > > some of the bits are checked in hardware. > > Yes and that's why it's a bit of a shame that the bits were defined as > UNKNOWN. We had an idea for how to improve error reports by using > those bits to link tag check faults to previous allocations, which was > precluded by the missing bits. Presumably if some future arch version propagated this information, we could add those bits into the tag bits mask when running on new enough hardware? Either way, I think we could do with a comment here. > > Hopefully a future revision of the architecture will define these bits > for tag check faults (at least optionally). If that ever happens and > support for the architecture extension is detected we could stop > masking the bits out in do_tag_check_fault and set > si_addr_tag_bits_mask to 0xffUL << 56, which would let userspace know > that the bits are now present. > > > For consistency, I wonder whether it makes sense to expose the bits as > > tag bits for watchpoint execeptions, even if they are left un-cleared in > > si_addr for historical reasons. > > I don't have a strong opinion on whether to do this or not, but it > seems like a nice property that the bits are either defined in si_addr > or in si_addr_tag_bits. I think we could leave the watchpoint > exception on arm64 as "weird for historical reasons" and insist that > any future architectures adopting tagged addresses handle the tag bits > uniformly. Ack -- I guess I don't have a strong opinion either. There's a risk of inventing problems here in order to solve them, so I agree we should keep things as simple and follow your current design. Cheers ---Dave
diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst index eab4323609b9..032c09a876f4 100644 --- a/Documentation/arm64/tagged-pointers.rst +++ b/Documentation/arm64/tagged-pointers.rst @@ -53,12 +53,21 @@ 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. +Non-zero tags are not preserved in the fault address fields +siginfo.si_addr or sigcontext.fault_address 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 in these fields. One exception to this rule is for +signals raised in response to watchpoint debug exceptions, where the +tag information will be preserved. + +The fault address tag is preserved in the si_addr_tag_bits field +of siginfo, which is set for signals raised in response to data aborts +and instruction aborts. The si_addr_tag_bits_mask field indicates +which bits of the field are valid. The validity of these fields is +indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags, +and the validity of si_xflags in turn is indicated by the kernel +indicating support for the sigaction.sa_flags flag SA_XFLAGS. 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..46f9b3c61896 --- /dev/null +++ b/arch/arm64/include/asm/signal.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ARM64_ASM_SIGNAL_H +#define __ARM64_ASM_SIGNAL_H + +#include <uapi/asm/signal.h> +#include <uapi/asm/siginfo.h> + +static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig, + unsigned long si_code) +{ + if (sig == SIGTRAP && si_code == TRAP_BRKPT) + return 0; + if (sig == SIGSEGV && si_code == SEGV_MTESERR) + return 0xfUL << 56; + return 0xffUL << 56; +} +#define arch_addr_tag_bits_mask arch_addr_tag_bits_mask + +#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 94c99c1c19e3..1d9d678cfc01 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/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c index 243a8cc3b41b..aa33674a4972 100644 --- a/arch/x86/kernel/signal_compat.c +++ b/arch/x86/kernel/signal_compat.c @@ -121,8 +121,8 @@ static inline void signal_compat_build_tests(void) #endif CHECK_CSI_OFFSET(_sigfault); - CHECK_CSI_SIZE (_sigfault, 8*sizeof(int)); - CHECK_SI_SIZE (_sigfault, 16*sizeof(int)); + CHECK_CSI_SIZE (_sigfault, 10*sizeof(int)); + CHECK_SI_SIZE (_sigfault, 20*sizeof(int)); BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x10); BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr) != 0x0C); @@ -141,6 +141,11 @@ static inline void signal_compat_build_tests(void) BUILD_BUG_ON(offsetof(siginfo_t, si_xflags) != 0x48); BUILD_BUG_ON(offsetof(compat_siginfo_t, si_xflags) != 0x28); + BUILD_BUG_ON(offsetof(siginfo_t, si_addr_tag_bits) != 0x50); + BUILD_BUG_ON(offsetof(siginfo_t, si_addr_tag_bits_mask) != 0x58); + BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr_tag_bits) != 0x2C); + BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr_tag_bits_mask) != 0x30); + CHECK_CSI_OFFSET(_sigpoll); CHECK_CSI_SIZE (_sigpoll, 2*sizeof(int)); CHECK_SI_SIZE (_sigpoll, 4*sizeof(int)); diff --git a/include/linux/compat.h b/include/linux/compat.h index ea77a24ce6a2..345d029adadc 100644 --- a/include/linux/compat.h +++ b/include/linux/compat.h @@ -239,6 +239,8 @@ typedef struct compat_siginfo { compat_uptr_t _pad[6]; }; u32 _xflags; + compat_uptr_t _addr_tag_bits; + compat_uptr_t _addr_tag_bits_mask; } _sigfault; /* SIGPOLL */ diff --git a/include/linux/signal.h b/include/linux/signal.h index 9b7fef0c559d..e12f211f5c12 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -480,4 +480,20 @@ struct seq_file; extern void render_sigset_t(struct seq_file *, const char *, sigset_t *); #endif +#ifndef arch_addr_tag_bits_mask +/* + * Given a signal and si_code which correspond to the _sigfault union member, + * if tag bits are present in the fault address which must appear in + * si_addr_tag_bits instead of si_addr, this hook must return a bitmask where 1 + * corresponds to bits appearing in si_addr_tag_bits and 0 corresponds to bits + * appearing in si_addr. The value returned by this function will also be + * available in si_addr_tag_bits_mask. + */ +static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig, + unsigned long si_code) +{ + return 0; +} +#endif + #endif /* _LINUX_SIGNAL_H */ diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 8158d5df666a..e5fe256c4979 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -94,6 +94,8 @@ union __sifields { void *_pad[6]; }; __u32 _xflags; + unsigned long _addr_tag_bits; + unsigned long _addr_tag_bits_mask; } _sigfault; /* SIGPOLL */ @@ -156,6 +158,8 @@ typedef struct siginfo { #define si_addr_lsb _sifields._sigfault._addr_lsb /* si_xflags is only valid if 0 < si_code < SI_KERNEL */ #define si_xflags _sifields._sigfault._xflags +#define si_addr_tag_bits _sifields._sigfault._addr_tag_bits +#define si_addr_tag_bits_mask _sifields._sigfault._addr_tag_bits_mask #define si_lower _sifields._sigfault._addr_bnd._lower #define si_upper _sifields._sigfault._addr_bnd._upper #define si_pkey _sifields._sigfault._addr_pkey._pkey @@ -298,6 +302,12 @@ typedef struct siginfo { #define EMT_TAGOVF 1 /* tag overflow */ #define NSIGEMT 1 +/* + * SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT si_xflags + */ +#define SIXFLAG_ADDR_TAG_BITS 1 +/* si_addr_tag_bits{,_mask} fields valid */ + /* * sigevent definitions * diff --git a/kernel/signal.c b/kernel/signal.c index 5c715a01942f..f41b40c9caf1 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1652,11 +1652,16 @@ void force_sigsegv(int sig) static void set_sigfault_common_fields(struct kernel_siginfo *info, int sig, int code, void __user *addr) { + unsigned long addr_long = (unsigned long)addr; + unsigned long tag_bits_mask = arch_addr_tag_bits_mask(sig, code); + info->si_signo = sig; info->si_errno = 0; info->si_code = code; - info->si_addr = addr; - info->si_xflags = 0; + info->si_addr = (void __user *)(addr_long & ~tag_bits_mask); + info->si_xflags = SIXFLAG_ADDR_TAG_BITS; + info->si_addr_tag_bits = addr_long & tag_bits_mask; + info->si_addr_tag_bits_mask = tag_bits_mask; } int force_sig_fault_to_task(int sig, int code, void __user *addr @@ -3271,6 +3276,13 @@ void copy_siginfo_to_external32(struct compat_siginfo *to, to->si_trapno = from->si_trapno; #endif to->si_xflags = from->si_xflags; + /* + * These assignments involve a truncation, but as with si_addr + * they will be derived from a 32-bit fault address so we + * should not expect any truncation in practice. + */ + to->si_addr_tag_bits = from->si_addr_tag_bits; + to->si_addr_tag_bits_mask = from->si_addr_tag_bits_mask; } switch (layout) { @@ -3347,6 +3359,8 @@ static int post_copy_siginfo_from_user32(kernel_siginfo_t *to, to->si_trapno = from->si_trapno; #endif to->si_xflags = from->si_xflags; + to->si_addr_tag_bits = from->si_addr_tag_bits; + to->si_addr_tag_bits_mask = from->si_addr_tag_bits_mask; } switch (layout) {
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, create a new pair of union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 there, together with a mask specifying which bits are valid. A flag is added to si_xflags to allow userspace to determine whether the values in the fields are valid. [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html Signed-off-by: Peter Collingbourne <pcc@google.com> Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446 --- 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 SIXFLAG_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 | 21 +++++--- arch/arm64/include/asm/exception.h | 2 +- arch/arm64/include/asm/signal.h | 19 +++++++ 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 ++++++++++++++----------- arch/x86/kernel/signal_compat.c | 9 +++- include/linux/compat.h | 2 + include/linux/signal.h | 16 ++++++ include/uapi/asm-generic/siginfo.h | 10 ++++ kernel/signal.c | 18 ++++++- 16 files changed, 148 insertions(+), 73 deletions(-) create mode 100644 arch/arm64/include/asm/signal.h