| Message ID | 1508631773-2502-2-git-send-email-alex.popov@linux.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sun, Oct 22, 2017 at 03:22:49AM +0300, Alexander Popov wrote: > The STACKLEAK feature erases the kernel stack before returning from > syscalls. That reduces the information which kernel stack leak bugs can > reveal and blocks some uninitialized stack variable attacks. Moreover, > STACKLEAK provides runtime checks for kernel stack overflow detection. > > This commit introduces the architecture-specific code filling the used > part of the kernel stack with a poison value before returning to the > userspace. Full STACKLEAK feature also contains the gcc plugin which > comes in a separate commit. > > The STACKLEAK feature is ported from grsecurity/PaX. More information at: > https://grsecurity.net/ > https://pax.grsecurity.net/ > > This code is modified from Brad Spengler/PaX Team's code in the last > public patch of grsecurity/PaX based on our understanding of the code. > Changes or omissions from the original code are ours and don't reflect > the original grsecurity/PaX code. > > Signed-off-by: Alexander Popov <alex.popov@linux.com> > --- > arch/Kconfig | 27 ++++++++++++ > arch/x86/Kconfig | 1 + > arch/x86/entry/common.c | 17 +++++-- > arch/x86/entry/entry_32.S | 69 +++++++++++++++++++++++++++++ > arch/x86/entry/entry_64.S | 95 ++++++++++++++++++++++++++++++++++++++++ > arch/x86/entry/entry_64_compat.S | 8 ++++ > arch/x86/include/asm/processor.h | 4 ++ > arch/x86/kernel/asm-offsets.c | 9 ++++ > arch/x86/kernel/process_32.c | 5 +++ > arch/x86/kernel/process_64.c | 5 +++ > include/linux/compiler.h | 4 ++ > 11 files changed, 241 insertions(+), 3 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index d789a89..e9ec94c 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -386,6 +386,13 @@ config SECCOMP_FILTER > > See Documentation/prctl/seccomp_filter.txt for details. > > +config HAVE_ARCH_STACKLEAK > + bool > + help > + An architecture should select this if it has the code which > + fills the used part of the kernel stack with the STACKLEAK_POISON > + value before returning from system calls. > + > config HAVE_GCC_PLUGINS > bool > help > @@ -516,6 +523,26 @@ config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE > in structures. This reduces the performance hit of RANDSTRUCT > at the cost of weakened randomization. > > +config GCC_PLUGIN_STACKLEAK > + bool "Erase the kernel stack before returning from syscalls" > + depends on GCC_PLUGINS > + depends on HAVE_ARCH_STACKLEAK > + help > + This option makes the kernel erase the kernel stack before it > + returns from a system call. That reduces the information which > + kernel stack leak bugs can reveal and blocks some uninitialized > + stack variable attacks. This option also provides runtime checks > + for kernel stack overflow detection. > + > + The tradeoff is the performance impact: on a single CPU system kernel > + compilation sees a 1% slowdown, other systems and workloads may vary > + and you are advised to test this feature on your expected workload > + before deploying it. > + > + This plugin was ported from grsecurity/PaX. More information at: > + * https://grsecurity.net/ > + * https://pax.grsecurity.net/ > + > config HAVE_CC_STACKPROTECTOR > bool > help > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 971feac..b7da58f 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -114,6 +114,7 @@ config X86 > select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT > select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT > select HAVE_ARCH_SECCOMP_FILTER > + select HAVE_ARCH_STACKLEAK > select HAVE_ARCH_TRACEHOOK > select HAVE_ARCH_TRANSPARENT_HUGEPAGE > select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c > index 03505ff..075487e 100644 > --- a/arch/x86/entry/common.c > +++ b/arch/x86/entry/common.c > @@ -45,6 +45,12 @@ __visible inline void enter_from_user_mode(void) > static inline void enter_from_user_mode(void) {} > #endif > > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > +asmlinkage void erase_kstack(void); > +#else > +static void erase_kstack(void) {} > +#endif > + > static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) > { > #ifdef CONFIG_X86_64 > @@ -81,8 +87,10 @@ static long syscall_trace_enter(struct pt_regs *regs) > emulated = true; > > if ((emulated || (work & _TIF_SYSCALL_TRACE)) && > - tracehook_report_syscall_entry(regs)) > + tracehook_report_syscall_entry(regs)) { > + erase_kstack(); > return -1L; > + } > > if (emulated) > return -1L; > @@ -116,9 +124,11 @@ static long syscall_trace_enter(struct pt_regs *regs) > sd.args[5] = regs->bp; > } > > - ret = __secure_computing(&sd); > - if (ret == -1) > + ret = secure_computing(&sd); Is there any reason to switch this from the __ version? This basically adds an additional check on the TIF_SECCOMP flag, but I'm not sure that's intentional with this patch. Cheers, Tycho
On 23.10.2017 16:17, Tycho Andersen wrote: > On Sun, Oct 22, 2017 at 03:22:49AM +0300, Alexander Popov wrote: >> The STACKLEAK feature erases the kernel stack before returning from >> syscalls. That reduces the information which kernel stack leak bugs can >> reveal and blocks some uninitialized stack variable attacks. Moreover, >> STACKLEAK provides runtime checks for kernel stack overflow detection. >> >> This commit introduces the architecture-specific code filling the used >> part of the kernel stack with a poison value before returning to the >> userspace. Full STACKLEAK feature also contains the gcc plugin which >> comes in a separate commit. >> >> The STACKLEAK feature is ported from grsecurity/PaX. More information at: >> https://grsecurity.net/ >> https://pax.grsecurity.net/ >> >> This code is modified from Brad Spengler/PaX Team's code in the last >> public patch of grsecurity/PaX based on our understanding of the code. >> Changes or omissions from the original code are ours and don't reflect >> the original grsecurity/PaX code. >> >> Signed-off-by: Alexander Popov <alex.popov@linux.com> >> --- [...] >> @@ -81,8 +87,10 @@ static long syscall_trace_enter(struct pt_regs *regs) >> emulated = true; >> >> if ((emulated || (work & _TIF_SYSCALL_TRACE)) && >> - tracehook_report_syscall_entry(regs)) >> + tracehook_report_syscall_entry(regs)) { >> + erase_kstack(); >> return -1L; >> + } >> >> if (emulated) >> return -1L; >> @@ -116,9 +124,11 @@ static long syscall_trace_enter(struct pt_regs *regs) >> sd.args[5] = regs->bp; >> } >> >> - ret = __secure_computing(&sd); >> - if (ret == -1) >> + ret = secure_computing(&sd); > > Is there any reason to switch this from the __ version? This basically > adds an additional check on the TIF_SECCOMP flag, but I'm not sure > that's intentional with this patch. Hello Tycho, thanks for your remark! Initially I took this change from the grsecurity patch, because it looked reasonable for me at that time. But now I doubt, thank you. Kees and Andy (Lutomirski), you are the authors of syscall_trace_enter(). Could you please have a look at this change? By the way, it seems that one erase_kstack() call is missing in that function. Could you please have a glance at the places where erase_kstack() is called? Thanks in advance. Best regards, Alexander
On Tue, Oct 24, 2017 at 2:30 PM, Alexander Popov <alex.popov@linux.com> wrote: > On 23.10.2017 16:17, Tycho Andersen wrote: >> On Sun, Oct 22, 2017 at 03:22:49AM +0300, Alexander Popov wrote: >>> The STACKLEAK feature erases the kernel stack before returning from >>> syscalls. That reduces the information which kernel stack leak bugs can >>> reveal and blocks some uninitialized stack variable attacks. Moreover, >>> STACKLEAK provides runtime checks for kernel stack overflow detection. >>> >>> This commit introduces the architecture-specific code filling the used >>> part of the kernel stack with a poison value before returning to the >>> userspace. Full STACKLEAK feature also contains the gcc plugin which >>> comes in a separate commit. >>> >>> The STACKLEAK feature is ported from grsecurity/PaX. More information at: >>> https://grsecurity.net/ >>> https://pax.grsecurity.net/ >>> >>> This code is modified from Brad Spengler/PaX Team's code in the last >>> public patch of grsecurity/PaX based on our understanding of the code. >>> Changes or omissions from the original code are ours and don't reflect >>> the original grsecurity/PaX code. >>> >>> Signed-off-by: Alexander Popov <alex.popov@linux.com> >>> --- > > [...] > >>> @@ -81,8 +87,10 @@ static long syscall_trace_enter(struct pt_regs *regs) >>> emulated = true; >>> >>> if ((emulated || (work & _TIF_SYSCALL_TRACE)) && >>> - tracehook_report_syscall_entry(regs)) >>> + tracehook_report_syscall_entry(regs)) { >>> + erase_kstack(); >>> return -1L; >>> + } >>> >>> if (emulated) >>> return -1L; >>> @@ -116,9 +124,11 @@ static long syscall_trace_enter(struct pt_regs *regs) >>> sd.args[5] = regs->bp; >>> } >>> >>> - ret = __secure_computing(&sd); >>> - if (ret == -1) >>> + ret = secure_computing(&sd); >> >> Is there any reason to switch this from the __ version? This basically >> adds an additional check on the TIF_SECCOMP flag, but I'm not sure >> that's intentional with this patch. > > Hello Tycho, thanks for your remark! > > Initially I took this change from the grsecurity patch, because it looked > reasonable for me at that time. But now I doubt, thank you. Yeah, I'd prefer this stay __secure_computing(). > Kees and Andy (Lutomirski), you are the authors of syscall_trace_enter(). Could > you please have a look at this change? > > By the way, it seems that one erase_kstack() call is missing in that function. > Could you please have a glance at the places where erase_kstack() is called? Errr, wouldn't erase_kstack() get called outside of seccomp? (i.e. via syscall_return_slowpath() or something later in the return path?) Or is there some reason for erasing the stack after seccomp processing but before running the syscall? -Kees
Hello Kees, On 31.10.2017 18:20, Kees Cook wrote: > On Tue, Oct 24, 2017 at 2:30 PM, Alexander Popov <alex.popov@linux.com> wrote: >> On 23.10.2017 16:17, Tycho Andersen wrote: >>> On Sun, Oct 22, 2017 at 03:22:49AM +0300, Alexander Popov wrote: >>>> The STACKLEAK feature erases the kernel stack before returning from >>>> syscalls. That reduces the information which kernel stack leak bugs can >>>> reveal and blocks some uninitialized stack variable attacks. Moreover, >>>> STACKLEAK provides runtime checks for kernel stack overflow detection. >>>> >>>> This commit introduces the architecture-specific code filling the used >>>> part of the kernel stack with a poison value before returning to the >>>> userspace. Full STACKLEAK feature also contains the gcc plugin which >>>> comes in a separate commit. >>>> >>>> The STACKLEAK feature is ported from grsecurity/PaX. More information at: >>>> https://grsecurity.net/ >>>> https://pax.grsecurity.net/ >>>> >>>> This code is modified from Brad Spengler/PaX Team's code in the last >>>> public patch of grsecurity/PaX based on our understanding of the code. >>>> Changes or omissions from the original code are ours and don't reflect >>>> the original grsecurity/PaX code. >>>> >>>> Signed-off-by: Alexander Popov <alex.popov@linux.com> >>>> --- >> >> [...] >> >>>> @@ -81,8 +87,10 @@ static long syscall_trace_enter(struct pt_regs *regs) >>>> emulated = true; >>>> >>>> if ((emulated || (work & _TIF_SYSCALL_TRACE)) && >>>> - tracehook_report_syscall_entry(regs)) >>>> + tracehook_report_syscall_entry(regs)) { >>>> + erase_kstack(); >>>> return -1L; >>>> + } >>>> >>>> if (emulated) >>>> return -1L; >>>> @@ -116,9 +124,11 @@ static long syscall_trace_enter(struct pt_regs *regs) >>>> sd.args[5] = regs->bp; >>>> } >>>> >>>> - ret = __secure_computing(&sd); >>>> - if (ret == -1) >>>> + ret = secure_computing(&sd); >>> >>> Is there any reason to switch this from the __ version? This basically >>> adds an additional check on the TIF_SECCOMP flag, but I'm not sure >>> that's intentional with this patch. >> >> Hello Tycho, thanks for your remark! >> >> Initially I took this change from the grsecurity patch, because it looked >> reasonable for me at that time. But now I doubt, thank you. > > Yeah, I'd prefer this stay __secure_computing(). Ok. >> Kees and Andy (Lutomirski), you are the authors of syscall_trace_enter(). Could >> you please have a look at this change? >> >> By the way, it seems that one erase_kstack() call is missing in that function. >> Could you please have a glance at the places where erase_kstack() is called? > > Errr, wouldn't erase_kstack() get called outside of seccomp? (i.e. via > syscall_return_slowpath() or something later in the return path?) Yes, erase_kstack() is called later in entry_SYSCALL_64 just after do_syscall_64. > Or is there some reason for erasing the stack after seccomp processing > but before running the syscall? Ah, it seems that PaX Team is doing that intentionally. I guess I've found the proof in his slides for H2HC conference (slide 38): https://pax.grsecurity.net/docs/PaXTeam-H2HC13-PaX-gcc-plugins.pdf "- Special paths for ptrace/auditing -- Low-level kernel entry/exit paths can diverge for ptrace/auditing and leave interesting information on the stack for the actual syscall code" Do you know which kind of interesting information is mentioned? And again, erase_kstack() is not called before 1 of 4 return statements in syscall_trace_enter(). IMHO it is a bug. Could you please verify that? Thanks! Best regards, Alexander
diff --git a/arch/Kconfig b/arch/Kconfig index d789a89..e9ec94c 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -386,6 +386,13 @@ config SECCOMP_FILTER See Documentation/prctl/seccomp_filter.txt for details. +config HAVE_ARCH_STACKLEAK + bool + help + An architecture should select this if it has the code which + fills the used part of the kernel stack with the STACKLEAK_POISON + value before returning from system calls. + config HAVE_GCC_PLUGINS bool help @@ -516,6 +523,26 @@ config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE in structures. This reduces the performance hit of RANDSTRUCT at the cost of weakened randomization. +config GCC_PLUGIN_STACKLEAK + bool "Erase the kernel stack before returning from syscalls" + depends on GCC_PLUGINS + depends on HAVE_ARCH_STACKLEAK + help + This option makes the kernel erase the kernel stack before it + returns from a system call. That reduces the information which + kernel stack leak bugs can reveal and blocks some uninitialized + stack variable attacks. This option also provides runtime checks + for kernel stack overflow detection. + + The tradeoff is the performance impact: on a single CPU system kernel + compilation sees a 1% slowdown, other systems and workloads may vary + and you are advised to test this feature on your expected workload + before deploying it. + + This plugin was ported from grsecurity/PaX. More information at: + * https://grsecurity.net/ + * https://pax.grsecurity.net/ + config HAVE_CC_STACKPROTECTOR bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 971feac..b7da58f 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -114,6 +114,7 @@ config X86 select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT select HAVE_ARCH_SECCOMP_FILTER + select HAVE_ARCH_STACKLEAK select HAVE_ARCH_TRACEHOOK select HAVE_ARCH_TRANSPARENT_HUGEPAGE select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 03505ff..075487e 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -45,6 +45,12 @@ __visible inline void enter_from_user_mode(void) static inline void enter_from_user_mode(void) {} #endif +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +asmlinkage void erase_kstack(void); +#else +static void erase_kstack(void) {} +#endif + static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) { #ifdef CONFIG_X86_64 @@ -81,8 +87,10 @@ static long syscall_trace_enter(struct pt_regs *regs) emulated = true; if ((emulated || (work & _TIF_SYSCALL_TRACE)) && - tracehook_report_syscall_entry(regs)) + tracehook_report_syscall_entry(regs)) { + erase_kstack(); return -1L; + } if (emulated) return -1L; @@ -116,9 +124,11 @@ static long syscall_trace_enter(struct pt_regs *regs) sd.args[5] = regs->bp; } - ret = __secure_computing(&sd); - if (ret == -1) + ret = secure_computing(&sd); + if (ret == -1) { + erase_kstack(); return ret; + } } #endif @@ -127,6 +137,7 @@ static long syscall_trace_enter(struct pt_regs *regs) do_audit_syscall_entry(regs, arch); + erase_kstack(); return ret ?: regs->orig_ax; } diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 50e0d2b..a7b0c52 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -75,6 +75,71 @@ #endif .endm +.macro erase_kstack +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + call erase_kstack +#endif +.endm + +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +/* For the detailed comments, see erase_kstack in entry_64.S */ +ENTRY(erase_kstack) + pushl %edi + pushl %ecx + pushl %eax + pushl %ebp + + movl PER_CPU_VAR(current_task), %ebp + mov TASK_lowest_stack(%ebp), %edi + mov $STACKLEAK_POISON, %eax + std + +1: + mov %edi, %ecx + and $THREAD_SIZE_asm - 1, %ecx + shr $2, %ecx + repne scasl + jecxz 2f + + cmp $2*16, %ecx + jc 2f + + mov $2*16, %ecx + repe scasl + jecxz 2f + jne 1b + +2: + cld + or $2*4, %edi + mov %esp, %ecx + sub %edi, %ecx + + cmp $THREAD_SIZE_asm, %ecx + jb 3f + ud2 + +3: + shr $2, %ecx + rep stosl + + /* + * TODO: sp0 on x86_32 is not reliable, right? + * Doubt because of the definition of cpu_current_top_of_stack + * in arch/x86/kernel/cpu/common.c. + */ + mov TASK_thread_sp0(%ebp), %edi + sub $128, %edi + mov %edi, TASK_lowest_stack(%ebp) + + popl %ebp + popl %eax + popl %ecx + popl %edi + ret +ENDPROC(erase_kstack) +#endif + /* * User gs save/restore * @@ -445,6 +510,8 @@ ENTRY(entry_SYSENTER_32) ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV + erase_kstack + /* Opportunistic SYSEXIT */ TRACE_IRQS_ON /* User mode traces as IRQs on. */ movl PT_EIP(%esp), %edx /* pt_regs->ip */ @@ -531,6 +598,8 @@ ENTRY(entry_INT80_32) call do_int80_syscall_32 .Lsyscall_32_done: + erase_kstack + restore_all: TRACE_IRQS_IRET .Lrestore_all_notrace: diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 4916725..189d843 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -59,6 +59,90 @@ END(native_usergs_sysret64) #endif .endm +.macro erase_kstack +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + call erase_kstack +#endif +.endm + +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +ENTRY(erase_kstack) + pushq %rdi + pushq %rcx + pushq %rax + pushq %r11 + + movq PER_CPU_VAR(current_task), %r11 + mov TASK_lowest_stack(%r11), %rdi + mov $STACKLEAK_POISON, %rax + std + + /* + * Let's search for the poison value in the stack. + * Start from the lowest_stack and go to the bottom (see std above). + */ +1: + mov %edi, %ecx + and $THREAD_SIZE_asm - 1, %ecx + shr $3, %ecx + repne scasq + jecxz 2f /* Didn't find it. Go to poisoning. */ + + /* + * Found the poison value in the stack. Go to poisoning if there are + * less than 16 qwords left. + */ + cmp $2*8, %ecx + jc 2f + + /* + * Check that 16 further qwords contain poison (avoid false positives). + * If so, the part of the stack below the address in %rdi is likely + * to be poisoned. Otherwise we need to search deeper. + */ + mov $2*8, %ecx + repe scasq + jecxz 2f /* Poison the upper part of the stack. */ + jne 1b /* Search deeper. */ + +2: + /* + * Prepare the counter for poisoning the kernel stack between + * %rdi and %rsp. Two qwords at the bottom of the stack are reserved + * and should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK). + */ + cld + or $2*8, %rdi + mov %esp, %ecx + sub %edi, %ecx + + /* Check that the counter value is sane. */ + cmp $THREAD_SIZE_asm, %rcx + jb 3f + ud2 + +3: + /* + * So let's write the poison value to the kernel stack. Start from the + * address in %rdi and move up (see cld above) to the address in %rsp + * (not included, used memory). + */ + shr $3, %ecx + rep stosq + + /* Set the lowest_stack value to the top_of_stack - 256. */ + mov TASK_thread_sp0(%r11), %rdi + sub $256, %rdi + mov %rdi, TASK_lowest_stack(%r11) + + popq %r11 + popq %rax + popq %rcx + popq %rdi + ret +ENDPROC(erase_kstack) +#endif + /* * When dynamic function tracer is enabled it will add a breakpoint * to all locations that it is about to modify, sync CPUs, update @@ -216,6 +300,8 @@ entry_SYSCALL_64_fastpath: testl $_TIF_ALLWORK_MASK, TASK_TI_flags(%r11) jnz 1f + erase_kstack + LOCKDEP_SYS_EXIT TRACE_IRQS_ON /* user mode is traced as IRQs on */ movq RIP(%rsp), %rcx @@ -245,6 +331,8 @@ entry_SYSCALL64_slow_path: call do_syscall_64 /* returns with IRQs disabled */ return_from_SYSCALL_64: + erase_kstack + RESTORE_EXTRA_REGS TRACE_IRQS_IRETQ /* we're about to change IF */ @@ -421,6 +509,7 @@ ENTRY(ret_from_fork) UNWIND_HINT_REGS movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ + erase_kstack TRACE_IRQS_ON /* user mode is traced as IRQS on */ SWAPGS jmp restore_regs_and_iret @@ -610,6 +699,12 @@ ret_from_intr: GLOBAL(retint_user) mov %rsp,%rdi call prepare_exit_to_usermode + + /* + * TODO: Do we need to call erase_kstack here? + * The PaX patch has it here commented out. + */ + TRACE_IRQS_IRETQ SWAPGS jmp restore_regs_and_iret diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index e26c25c..f79cbf4 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -18,6 +18,12 @@ .section .entry.text, "ax" + .macro erase_kstack +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + call erase_kstack +#endif + .endm + /* * 32-bit SYSENTER entry. * @@ -228,6 +234,7 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe) /* Opportunistic SYSRET */ sysret32_from_system_call: + erase_kstack TRACE_IRQS_ON /* User mode traces as IRQs on. */ movq RBX(%rsp), %rbx /* pt_regs->rbx */ movq RBP(%rsp), %rbp /* pt_regs->rbp */ @@ -335,6 +342,7 @@ ENTRY(entry_INT80_compat) .Lsyscall_32_done: /* Go back to user mode. */ + erase_kstack TRACE_IRQS_ON SWAPGS jmp restore_regs_and_iret diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index b390ff7..c6eaf2d 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -477,6 +477,10 @@ struct thread_struct { mm_segment_t addr_limit; +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + unsigned long lowest_stack; +#endif + unsigned int sig_on_uaccess_err:1; unsigned int uaccess_err:1; /* uaccess failed */ diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c index de827d6..4ed7451 100644 --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -37,6 +37,10 @@ void common(void) { BLANK(); OFFSET(TASK_TI_flags, task_struct, thread_info.flags); OFFSET(TASK_addr_limit, task_struct, thread.addr_limit); +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + OFFSET(TASK_lowest_stack, task_struct, thread.lowest_stack); + OFFSET(TASK_thread_sp0, task_struct, thread.sp0); +#endif BLANK(); OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx); @@ -73,6 +77,11 @@ void common(void) { OFFSET(PV_MMU_read_cr2, pv_mmu_ops, read_cr2); #endif +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + BLANK(); + DEFINE(THREAD_SIZE_asm, THREAD_SIZE); +#endif + #ifdef CONFIG_XEN BLANK(); OFFSET(XEN_vcpu_info_mask, vcpu_info, evtchn_upcall_mask); diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 1196625..c7345d2 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -136,6 +136,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, p->thread.sp0 = (unsigned long) (childregs+1); memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps)); +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + p->thread.lowest_stack = (unsigned long)task_stack_page(p) + + 2 * sizeof(unsigned long); +#endif + if (unlikely(p->flags & PF_KTHREAD)) { /* kernel thread */ memset(childregs, 0, sizeof(struct pt_regs)); diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 302e7b2..65ba73f 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -283,6 +283,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, p->thread.sp = (unsigned long) fork_frame; p->thread.io_bitmap_ptr = NULL; +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + p->thread.lowest_stack = (unsigned long)task_stack_page(p) + + 2 * sizeof(unsigned long); +#endif + savesegment(gs, p->thread.gsindex); p->thread.gsbase = p->thread.gsindex ? 0 : me->thread.gsbase; savesegment(fs, p->thread.fsindex); diff --git a/include/linux/compiler.h b/include/linux/compiler.h index e95a263..916f02d 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -624,4 +624,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s (_________p1); \ }) +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +# define STACKLEAK_POISON -0xBEEF +#endif + #endif /* __LINUX_COMPILER_H */
The STACKLEAK feature erases the kernel stack before returning from syscalls. That reduces the information which kernel stack leak bugs can reveal and blocks some uninitialized stack variable attacks. Moreover, STACKLEAK provides runtime checks for kernel stack overflow detection. This commit introduces the architecture-specific code filling the used part of the kernel stack with a poison value before returning to the userspace. Full STACKLEAK feature also contains the gcc plugin which comes in a separate commit. The STACKLEAK feature is ported from grsecurity/PaX. More information at: https://grsecurity.net/ https://pax.grsecurity.net/ This code is modified from Brad Spengler/PaX Team's code in the last public patch of grsecurity/PaX based on our understanding of the code. Changes or omissions from the original code are ours and don't reflect the original grsecurity/PaX code. Signed-off-by: Alexander Popov <alex.popov@linux.com> --- arch/Kconfig | 27 ++++++++++++ arch/x86/Kconfig | 1 + arch/x86/entry/common.c | 17 +++++-- arch/x86/entry/entry_32.S | 69 +++++++++++++++++++++++++++++ arch/x86/entry/entry_64.S | 95 ++++++++++++++++++++++++++++++++++++++++ arch/x86/entry/entry_64_compat.S | 8 ++++ arch/x86/include/asm/processor.h | 4 ++ arch/x86/kernel/asm-offsets.c | 9 ++++ arch/x86/kernel/process_32.c | 5 +++ arch/x86/kernel/process_64.c | 5 +++ include/linux/compiler.h | 4 ++ 11 files changed, 241 insertions(+), 3 deletions(-)