Commit 291fd835 authored by Chang S. Bae's avatar Chang S. Bae Committed by Thomas Gleixner

selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write

The test validates that the selector is not changed when a ptracer writes
the ptracee's GS base.
Originally-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200528201402.1708239-16-sashal@kernel.org
parent 82c0c7d2
...@@ -465,7 +465,7 @@ static void test_ptrace_write_gsbase(void) ...@@ -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, base; unsigned long gs;
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);
...@@ -481,7 +481,6 @@ static void test_ptrace_write_gsbase(void) ...@@ -481,7 +481,6 @@ 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
...@@ -489,11 +488,21 @@ static void test_ptrace_write_gsbase(void) ...@@ -489,11 +488,21 @@ static void test_ptrace_write_gsbase(void)
* selector value is changed or not by the GSBASE write in * selector value is changed or not by the GSBASE write in
* a ptracer. * a ptracer.
*/ */
if (gs == 0 && base == 0xFF) { if (gs != *shared_scratch) {
printf("[OK]\tGS was reset as expected\n");
} else {
nerrs++; nerrs++;
printf("[FAIL]\tGS=0x%lx, GSBASE=0x%lx (should be 0, 0xFF)\n", gs, base); printf("[FAIL]\tGS changed to %lx\n", gs);
/*
* On older kernels, poking a nonzero value into the
* base would zero the selector. On newer kernels,
* this behavior has changed -- poking the base
* changes only the base and, if FSGSBASE is not
* available, this may not effect.
*/
if (gs == 0)
printf("\tNote: this is expected behavior on older kernels.\n");
} else {
printf("[OK]\tGS remained 0x%hx\n", *shared_scratch);
} }
} }
......
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