Messages in this thread | | | Date | Thu, 21 May 2020 16:02:50 -0700 | From | Kees Cook <> | Subject | Re: [RFC PATCH 5/5] selftest/x86: Add CET quick test |
| |
On Thu, May 21, 2020 at 02:17:20PM -0700, Yu-cheng Yu wrote: > Introduce a quick test to verify shadow stack and IBT are working.
Cool! :)
I'd love to see either more of a commit log or more comments in the test code itself. I had to spend a bit of time trying to understand how the test was working. (i.e. using ucontext to "reset", using segv handler to catch some of them, etc.) I have not yet figured out why you need to send USR1/USR2 for two of them instead of direct calls?
More notes below...
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > --- > tools/testing/selftests/x86/Makefile | 2 +- > tools/testing/selftests/x86/cet_quick_test.c | 128 +++++++++++++++++++ > 2 files changed, 129 insertions(+), 1 deletion(-) > create mode 100644 tools/testing/selftests/x86/cet_quick_test.c > > diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile > index f1bf5ab87160..26e68272117a 100644 > --- a/tools/testing/selftests/x86/Makefile > +++ b/tools/testing/selftests/x86/Makefile > @@ -14,7 +14,7 @@ CAN_BUILD_CET := $(shell ./check_cc.sh $(CC) trivial_program.c -fcf-protection) > TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt test_mremap_vdso \ > check_initial_reg_state sigreturn iopl ioperm \ > protection_keys test_vdso test_vsyscall mov_ss_trap \ > - syscall_arg_fault > + syscall_arg_fault cet_quick_test > TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \ > test_FCMOV test_FCOMI test_FISTTP \ > vdso_restorer > diff --git a/tools/testing/selftests/x86/cet_quick_test.c b/tools/testing/selftests/x86/cet_quick_test.c > new file mode 100644 > index 000000000000..e84bbbcfd26f > --- /dev/null > +++ b/tools/testing/selftests/x86/cet_quick_test.c > @@ -0,0 +1,128 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* Quick tests to verify Shadow Stack and IBT are working */ > + > +#include <stdio.h> > +#include <stdlib.h> > +#include <signal.h> > +#include <string.h> > +#include <ucontext.h> > + > +ucontext_t ucp; > +int result[4] = {-1, -1, -1, -1};
I think you likely want three states: no signal, failed, and okay. Perhaps -1 for "no signal" like you have above, zero for failed, and 1 for okay.
> +int test_id; > + > +void stack_hacked(unsigned long x) > +{ > + result[test_id] = -1;
So this is set to 0: "I absolutely bypassed the protection".
> + test_id++; > + setcontext(&ucp); > +} > + > +#pragma GCC push_options > +#pragma GCC optimize ("O0")
Can you avoid compiler-specific pragmas? (Or verify that Clang also behaves correctly here?) Maybe it's better to just build the entire file with -O0 in the Makefile?
> +void ibt_violation(void) > +{ > +#ifdef __i386__ > + asm volatile("lea 1f, %eax"); > + asm volatile("jmp *%eax"); > +#else > + asm volatile("lea 1f, %rax"); > + asm volatile("jmp *%rax"); > +#endif > + asm volatile("1:"); > + result[test_id] = -1;
Set to 0, and if the segv doesn't see it, we know for sure it failed.
> + test_id++; > + setcontext(&ucp); > +} > + > +void shstk_violation(void) > +{ > +#ifdef __i386__ > + unsigned long x = 0; > + > + ((unsigned long *)&x)[2] = (unsigned long)stack_hacked; > +#else > + unsigned long long x = 0; > + > + ((unsigned long long *)&x)[2] = (unsigned long)stack_hacked; > +#endif > +} > +#pragma GCC pop_options > + > +void segv_handler(int signum, siginfo_t *si, void *uc) > +{
Does anything in siginfo_t indicate which kind of failure you're detecting? It'd be nice to verify test_id matches the failure mode being tested.
> + result[test_id] = 0; > + test_id++; > + setcontext(&ucp); > +} > + > +void user1_handler(int signum, siginfo_t *si, void *uc) > +{ > + shstk_violation(); > +} > + > +void user2_handler(int signum, siginfo_t *si, void *uc) > +{ > + ibt_violation(); > +} > + > +int main(int argc, char *argv[]) > +{ > + struct sigaction sa; > + int r; > + > + r = sigemptyset(&sa.sa_mask); > + if (r) > + return -1; > + > + sa.sa_flags = SA_SIGINFO; > + > + /* > + * Control protection fault handler > + */ > + sa.sa_sigaction = segv_handler; > + r = sigaction(SIGSEGV, &sa, NULL); > + if (r) > + return -1; > + > + /* > + * Handler to test Shadow stack > + */ > + sa.sa_sigaction = user1_handler; > + r = sigaction(SIGUSR1, &sa, NULL); > + if (r) > + return -1; > + > + /* > + * Handler to test IBT > + */ > + sa.sa_sigaction = user2_handler; > + r = sigaction(SIGUSR2, &sa, NULL); > + if (r) > + return -1; > + > + test_id = 0; > + r = getcontext(&ucp); > + if (r) > + return -1; > + > + if (test_id == 0) > + shstk_violation(); > + else if (test_id == 1) > + ibt_violation(); > + else if (test_id == 2) > + raise(SIGUSR1); > + else if (test_id == 3) > + raise(SIGUSR2); > + > + r = 0; > + printf("[%s]\tShadow stack\n", result[0] ? "FAIL":"OK");
Then these are result[0] == -1 ? "untested" : (result[0] ? "OK" : "FAIL"))
> + r += result[0]; > + printf("[%s]\tIBT\n", result[1] ? "FAIL":"OK"); > + r += result[1]; > + printf("[%s]\tShadow stack in signal\n", result[2] ? "FAIL":"OK"); > + r += result[2]; > + printf("[%s]\tIBT in signal\n", result[3] ? "FAIL":"OK"); > + r += result[3]; > + return r; > +} > -- > 2.21.0 >
-- Kees Cook
| |