[RFC PATCH 3/5] selftest/x86: Fix sigreturn_64 test.

Yu-cheng Yu
2020-05-21T21:17:47Z

When shadow stack is enabled, selftests/x86/sigreturn_64 triggers a fault
when doing sigreturn to 32-bit context but the task's shadow stack pointer
is above 32-bit address range. Fix it by:

- Allocate a small shadow stack below 32-bit address,
- Switch to the new shadow stack,
- Run tests,
- Switch back to the original 64-bit shadow stack.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
tools/testing/selftests/x86/sigreturn.c | 28 +++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/tools/testing/selftests/x86/sigreturn.c b/tools/testing/selftests/x86/sigreturn.c
index 57c4f67f16ef..5bcd74d416ff 100644
--- a/tools/testing/selftests/x86/sigreturn.c
+++ b/tools/testing/selftests/x86/sigreturn.c
@@ -45,6 +45,14 @@
#include <stdbool.h>
#include <sys/ptrace.h>
#include <sys/user.h>
+#include <x86intrin.h>
+#include <asm/prctl.h>
+#include <sys/prctl.h>
+
+#ifdef __x86_64__
+int arch_prctl(int code, unsigned long *addr);
+#define ARCH_CET_ALLOC_SHSTK 0x3004
+#endif

/* Pull in AR_xyz defines. */
typedef unsigned int u32;
@@ -766,6 +774,20 @@ int main()
int total_nerrs = 0;
unsigned short my_cs, my_ss;

+#ifdef __x86_64__
+ /* Alloc a shadow stack within 32-bit address range */
+ unsigned long arg, ssp_64, ssp_32;
+ ssp_64 = _get_ssp();
+
+ if (ssp_64 != 0) {
+ arg = 0x1001;
+ arch_prctl(ARCH_CET_ALLOC_SHSTK, &arg);
+ ssp_32 = arg + 0x1000 - 8;
+ asm volatile("RSTORSSP (%0)\n":: "r" (ssp_32));
+ asm volatile("SAVEPREVSSP");
+ }
+#endif
+
asm volatile ("mov %%cs,%0" : "=r" (my_cs));
asm volatile ("mov %%ss,%0" : "=r" (my_ss));
setup_ldt();
@@ -870,6 +892,12 @@ int main()

#ifdef __x86_64__
total_nerrs += test_nonstrict_ss();
+
+ if (ssp_64 != 0) {
+ ssp_64 -= 8;
+ asm volatile("RSTORSSP (%0)\n":: "r" (ssp_64));
+ asm volatile("SAVEPREVSSP");
+ }
#endif

return total_nerrs ? 1 : 0;
--
2.21.0