Messages in this thread | | | From | Thomas Garnier <> | Date | Mon, 7 Aug 2017 10:42:14 -0700 | Subject | Re: [PATCH v2 2/3] arm/syscalls: Optimize address limit check |
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On Mon, Aug 7, 2017 at 10:35 AM, Kees Cook <keescook@chromium.org> wrote: > On Wed, Jul 26, 2017 at 10:00 AM, Thomas Garnier <thgarnie@google.com> wrote: >> Disable the generic address limit check in favor of an architecture >> specific optimized implementation. The generic implementation using >> pending work flags did not work well with ARM and alignment faults. >> >> The address limit is checked on each syscall return path to user-mode >> path as well as the irq user-mode return function. If the address limit >> was changed, a function is called to stop the kernel with an explicit >> message. >> >> The address limit check has to be done before any pending work because >> they can reset the address limit. For example the lkdtm address limit >> check does not work because the signal to kill the process will reset >> the user-mode address limit. >> >> Signed-off-by: Thomas Garnier <thgarnie@google.com> >> --- >> arch/arm/kernel/entry-common.S | 11 +++++++++++ >> arch/arm/kernel/signal.c | 5 +++++ >> 2 files changed, 16 insertions(+) >> >> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S >> index 0b60adf4a5d9..99c908226065 100644 >> --- a/arch/arm/kernel/entry-common.S >> +++ b/arch/arm/kernel/entry-common.S >> @@ -12,6 +12,7 @@ >> #include <asm/unistd.h> >> #include <asm/ftrace.h> >> #include <asm/unwind.h> >> +#include <asm/memory.h> >> #ifdef CONFIG_AEABI >> #include <asm/unistd-oabi.h> >> #endif >> @@ -48,10 +49,14 @@ ret_fast_syscall: >> UNWIND(.fnstart ) >> UNWIND(.cantunwind ) >> disable_irq_notrace @ disable interrupts >> + ldr r2, [tsk, #TI_ADDR_LIMIT] >> + cmp r2, #TASK_SIZE >> + blne addr_limit_check_failed >> ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing >> tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK >> bne fast_work_pending >> >> + >> /* perform architecture specific actions before user return */ >> arch_ret_to_user r1, lr >> >> @@ -74,6 +79,9 @@ ret_fast_syscall: >> UNWIND(.cantunwind ) >> str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 >> disable_irq_notrace @ disable interrupts >> + ldr r2, [tsk, #TI_ADDR_LIMIT] >> + cmp r2, #TASK_SIZE >> + blne addr_limit_check_failed >> ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing >> tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK >> beq no_work_pending >> @@ -106,6 +114,9 @@ ENTRY(ret_to_user) >> ret_slow_syscall: >> disable_irq_notrace @ disable interrupts >> ENTRY(ret_to_user_from_irq) >> + ldr r2, [tsk, #TI_ADDR_LIMIT] >> + cmp r2, #TASK_SIZE >> + blne addr_limit_check_failed >> ldr r1, [tsk, #TI_FLAGS] >> tst r1, #_TIF_WORK_MASK >> bne slow_work_pending >> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c >> index 5814298ef0b7..5769c15cff89 100644 >> --- a/arch/arm/kernel/signal.c >> +++ b/arch/arm/kernel/signal.c >> @@ -673,3 +673,8 @@ struct page *get_signal_page(void) >> >> return page; >> } >> + >> +asmlinkage void addr_limit_check_failed(void) >> +{ >> + panic("Incorrect address limit while returning to user-mode."); >> +} > > Instead of taking the entire system down, how about a WARN/kill combo > instead? If it's too late for "force_sig(SIGKILL, current)", then > likely we should perform a "do_group_exit(SIGKILL)".
Sure, why not. I can also change the others architectures to move to a do_group_exit(SIGKILL).
Before the next iteration, I want to know if Russel has any feedback on this implementation, given the previous thread.
> > -Kees > > -- > Kees Cook > Pixel Security
-- Thomas
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