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

This validates that GS and GSBASE are independently preserved in
ptracer commands.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Link: https://lkml.kernel.org/r/1557309753-24073-16-git-send-email-chang.seok.bae@intel.com

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index afd0298..21fd4f9 100644 (file)
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -470,7 +470,7 @@ static void test_ptrace_write_gsbase(void)
        wait(&status);
 
        if (WSTOPSIG(status) == SIGTRAP) {
-               unsigned long gs;
+               unsigned long gs, base;
                unsigned long gs_offset = USER_REGS_OFFSET(gs);
                unsigned long base_offset = USER_REGS_OFFSET(gs_base);
 
@@ -486,6 +486,7 @@ static void test_ptrace_write_gsbase(void)
                        err(1, "PTRACE_POKEUSER");
 
                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
@@ -496,8 +497,14 @@ static void test_ptrace_write_gsbase(void)
                if (gs != 0x7) {
                        nerrs++;
                        printf("[FAIL]\tGS changed to %lx\n", gs);
+               } else if (have_fsgsbase && (base != 0xFF)) {
+                       nerrs++;
+                       printf("[FAIL]\tGSBASE changed to %lx\n", base);
                } else {
-                       printf("[OK]\tGS remained 0x7\n");
+                       printf("[OK]\tGS remained 0x7 %s");
+                       if (have_fsgsbase)
+                               printf("and GSBASE changed to 0xFF");
+                       printf("\n");
                }
        }