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SubjectRe: [PATCH v2 1/4] kselftests/arm64: add a basic Pointer Authentication test
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Hi Boyan,

On 8/31/20 4:34 PM, Boyan Karatotev wrote:
> PAuth signs and verifies return addresses on the stack. It does so by
> inserting a Pointer Authentication code (PAC) into some of the unused top
> bits of an address. This is achieved by adding paciasp/autiasp instructions
> at the beginning and end of a function.
>
> This feature is partially backwards compatible with earlier versions of the
> ARM architecture. To coerce the compiler into emitting fully backwards
> compatible code the main file is compiled to target an earlier ARM version.
> This allows the tests to check for the feature and print meaningful error
> messages instead of crashing.
>
> Add a test to verify that corrupting the return address results in a
> SIGSEGV on return.
>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
> Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
> ---
> tools/testing/selftests/arm64/Makefile | 2 +-

[...]

> +
> +/* check that a corrupted PAC results in SIGSEGV */
> +TEST_SIGNAL(corrupt_pac, SIGSEGV)
> +{
> + ASSERT_PAUTH_ENABLED();
> +
> + pac_corruptor();

With 8.6-Pauth extension merged in arm tree [1]. It makes sense to
verify PAC corruption for both SIGSEGV and SIGILL signals.

Code something like below handles both the cases.

-----------------------------------------------------------------------------------
int exec_sign_all(struct signatures *signed_vals, size_t val)
@@ -187,12 +188,29 @@ int exec_sign_all(struct signatures *signed_vals,
size_t val)
return 0;
}

-/* check that a corrupted PAC results in SIGSEGV */
-TEST_SIGNAL(corrupt_pac, SIGSEGV)
+sigjmp_buf jmpbuf;
+void pac_signal_handler(int signum, siginfo_t *si, void *uc)
{
- ASSERT_PAUTH_ENABLED();
+ if (signum == SIGSEGV || signum == SIGILL) {
+ siglongjmp(jmpbuf, 1);
+ }
+}
+
+/* check that a corrupted PAC results in SIGSEGV or SIGILL */
+TEST(corrupt_pac)
+{
+ struct sigaction sa;

- pac_corruptor();
+ ASSERT_PAUTH_ENABLED();
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ sa.sa_sigaction = pac_signal_handler;
+ sa.sa_flags = SA_SIGINFO;
+ sigemptyset(&sa.sa_mask);
+ sigaction(SIGSEGV, &sa, NULL);
+ sigaction(SIGILL, &sa, NULL);
+ pac_corruptor();
+ ASSERT_TRUE(0) TH_LOG("SIGSEGV/SIGILL signal did not
occur");
+ }
}

/*
@@ -265,7 +283,7 @@ TEST(single_thread_different_keys)

tmp = n_same_single_set(&signed_vals, nkeys);
---------------------------------------------------------------------------------------


Thanks,
Amit Daniel

[1]:
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/ptrauth

Regards,
Amit Daniel
> +}
> +
> +TEST_HARNESS_MAIN

[...]

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