[tip:x86/cpu] selftests/x86/fsgsbase: Test ptracer-induced GSBASE write with FSGSBASE

[tip-bot for Chang S. Bae]

Commit-ID:  a87730cc3acc475eff12ddde3f7d5687371b5c76
Gitweb:     https://git.kernel.org/tip/a87730cc3acc475eff12ddde3f7d5687371b5c76
Author:     Chang S. Bae <chang.seok.bae@xxxxxxxxx>
AuthorDate: Wed, 8 May 2019 03:02:30 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Sat, 22 Jun 2019 11:38:56 +0200

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@xxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Ravi Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Link: https://lkml.kernel.org/r/1557309753-24073-16-git-send-email-chang.seok.bae@xxxxxxxxx

---
 tools/testing/selftests/x86/fsgsbase.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index afd029897c79..21fd4f94b5b0 100644
--- 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");
 		}
 	}