The following commit has been merged into the x86/fsgsbase branch of tip:
Commit-ID: 1b9abd1755ad947d7c9913e92e7837b533124c90
Gitweb: https://git.kernel.org/tip/1b9abd1755ad947d7c9913e92e7837b533124c90
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Wed, 26 Aug 2020 10:00:46 -07:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 26 Aug 2020 20:54:18 +02:00
selftests/x86/fsgsbase: Test PTRACE_PEEKUSER for GSBASE with invalid LDT GS
This tests commit:
8ab49526b53d ("x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task")
Unpatched kernels will OOPS.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/c618ae86d1f757e01b1a8e79869f553cb88acf9a.1598461151.git.luto@xxxxxxxxxx
---
tools/testing/selftests/x86/fsgsbase.c | 65 +++++++++++++++++++++++++-
1 file changed, 65 insertions(+)
diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 0056e25..7161cfc 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -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) {
|