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SubjectRe: [PATCH v13 16/16] selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE
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On 5/28/20 2:14 PM, Sasha Levin wrote:
> From: "Chang S. Bae" <chang.seok.bae@intel.com>
>
> This validates that GS selector and base are independently preserved in
> ptrace commands.
>
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> tools/testing/selftests/x86/fsgsbase.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
> index 950a48b2e366..9a4349813a30 100644
> --- a/tools/testing/selftests/x86/fsgsbase.c
> +++ b/tools/testing/selftests/x86/fsgsbase.c
> @@ -465,7 +465,7 @@ static void test_ptrace_write_gsbase(void)
> wait(&status);
>
> if (WSTOPSIG(status) == SIGTRAP) {
> - unsigned long gs;
> + unsigned long gs, base;
> unsigned long gs_offset = USER_REGS_OFFSET(gs);
> unsigned long base_offset = USER_REGS_OFFSET(gs_base);
>
> @@ -481,6 +481,7 @@ static void test_ptrace_write_gsbase(void)
> err(1, "PTRACE_POKEUSER");
>
> gs = ptrace(PTRACE_PEEKUSER, child, gs_offset, NULL);
> + base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);
>
> /*
> * In a non-FSGSBASE system, the nonzero selector will load
> @@ -501,8 +502,14 @@ static void test_ptrace_write_gsbase(void)
> */
> if (gs == 0)
> printf("\tNote: this is expected behavior on older kernels.\n");

I know this hasn't changed. Please clarify what is "this" in this
message.

> + } else if (have_fsgsbase && (base != 0xFF)) {
> + nerrs++;
> + printf("[FAIL]\tGSBASE changed to %lx\n", base);
> } else {
> - printf("[OK]\tGS remained 0x%hx\n", *shared_scratch);
> + printf("[OK]\tGS remained 0x%hx", *shared_scratch);
> + if (have_fsgsbase)
> + printf(" and GSBASE changed to 0xFF");
> + printf("\n");
> }
> }
>
>

thanks,
-- Shuah

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