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selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE

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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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200528201402.1708239-17-sashal@kernel.org
This commit is contained in:
Chang S. Bae 2020-05-28 16:14:02 -04:00 • committed by Thomas Gleixner
parent 291fd83569
commit 5e7ec8578f
1 changed files with 9 additions and 2 deletions
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11
tools/testing/selftests/x86/fsgsbase.c
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@ -465,7 +465,7 @@ static void test_ptrace_write_gsbase(void)
wait(&status); wait(&status);
if (WSTOPSIG(status) == SIGTRAP) { if (WSTOPSIG(status) == SIGTRAP) {
unsigned long gs; unsigned long gs, base;
unsigned long gs_offset = USER_REGS_OFFSET(gs); unsigned long gs_offset = USER_REGS_OFFSET(gs);
unsigned long base_offset = USER_REGS_OFFSET(gs_base); unsigned long base_offset = USER_REGS_OFFSET(gs_base);
@ -481,6 +481,7 @@ static void test_ptrace_write_gsbase(void)
err(1, "PTRACE_POKEUSER"); err(1, "PTRACE_POKEUSER");
gs = ptrace(PTRACE_PEEKUSER, child, gs_offset, NULL); 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 * In a non-FSGSBASE system, the nonzero selector will load
@ -501,8 +502,14 @@ static void test_ptrace_write_gsbase(void)
*/ */
if (gs == 0) if (gs == 0)
printf("\tNote: this is expected behavior on older kernels.\n"); printf("\tNote: this is expected behavior on older kernels.\n");
} else if (have_fsgsbase && (base != 0xFF)) {
nerrs++;
printf("[FAIL]\tGSBASE changed to %lx\n", base);
} else { } 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");
} }
} }