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selftests/x86/fsgsbase: Test PTRACE_PEEKUSER for GSBASE with invalid LDT GS

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This tests commit:

  8ab49526b5 ("x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task")

Unpatched kernels will OOPS.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/c618ae86d1f757e01b1a8e79869f553cb88acf9a.1598461151.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2020-08-26 10:00:46 -07:00 committed by Ingo Molnar
parent ab2dd17333
commit 1b9abd1755
1 changed files with 65 additions and 0 deletions
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65
tools/testing/selftests/x86/fsgsbase.c
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@ -443,6 +443,68 @@ static void test_unexpected_base(void)
#define USER_REGS_OFFSET(r) offsetof(struct user_regs_struct, r)
static void test_ptrace_write_gs_read_base(void)
{
int status;
pid_t child = fork();
if (child < 0)
err(1, "fork");
if (child == 0) {
printf("[RUN]\tPTRACE_POKE GS, read GSBASE back\n");
printf("[RUN]\tARCH_SET_GS to 1\n");
if (syscall(SYS_arch_prctl, ARCH_SET_GS, 1) != 0)
err(1, "ARCH_SET_GS");
if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0)
err(1, "PTRACE_TRACEME");
raise(SIGTRAP);
_exit(0);
}
wait(&status);
if (WSTOPSIG(status) == SIGTRAP) {
unsigned long base;
unsigned long gs_offset = USER_REGS_OFFSET(gs);
unsigned long base_offset = USER_REGS_OFFSET(gs_base);
/* Read the initial base. It should be 1. */
base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);
if (base == 1) {
printf("[OK]\tGSBASE started at 1\n");
} else {
nerrs++;
printf("[FAIL]\tGSBASE started at 0x%lx\n", base);
}
printf("[RUN]\tSet GS = 0x7, read GSBASE\n");
/* Poke an LDT selector into GS. */
if (ptrace(PTRACE_POKEUSER, child, gs_offset, 0x7) != 0)
err(1, "PTRACE_POKEUSER");
/* And read the base. */
base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);
if (base == 0 || base == 1) {
printf("[OK]\tGSBASE reads as 0x%lx with invalid GS\n", base);
} else {
nerrs++;
printf("[FAIL]\tGSBASE=0x%lx (should be 0 or 1)\n", base);
}
}
ptrace(PTRACE_CONT, child, NULL, NULL);
wait(&status);
if (!WIFEXITED(status))
printf("[WARN]\tChild didn't exit cleanly.\n");
}
static void test_ptrace_write_gsbase(void)
{
int status;
@ -529,6 +591,9 @@ int main()
shared_scratch = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_SHARED, -1, 0);
/* Do these tests before we have an LDT. */
test_ptrace_write_gs_read_base();
/* Probe FSGSBASE */
sethandler(SIGILL, sigill, 0);
if (sigsetjmp(jmpbuf, 1) == 0) {