selftests/seccomp: Avoid redundant register flushes

When none of the registers have changed, don't flush them back. This can happen if the architecture uses a non-register way to change the syscall (e.g. arm64) , and a return value hasn't been written. Signed-off-by: Kees Cook <[email protected]> Link: https://lore.kernel.org/lkml/[email protected] Acked-by: Christian Brauner <[email protected]>
tonyvar · Sep 19, 2020 · e4e8e5d · e4e8e5d
1 parent dc2ad16
commit e4e8e5d
Showing 1 changed file with 4 additions and 2 deletions.
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1859,11 +1859,12 @@ int get_syscall(struct __test_metadata *_metadata, pid_t tracee)
 void change_syscall(struct __test_metadata *_metadata,
 		    pid_t tracee, int syscall, int result)
 {
-	ARCH_REGS regs;
+	ARCH_REGS orig, regs;
 
 	EXPECT_EQ(0, ARCH_GETREGS(regs)) {
 		return;
 	}
+	orig = regs;
 
 	SYSCALL_NUM_SET(regs, syscall);
 
@@ -1876,7 +1877,8 @@ void change_syscall(struct __test_metadata *_metadata,
 #endif
 
 	/* Flush any register changes made. */
-	EXPECT_EQ(0, ARCH_SETREGS(regs));
+	if (memcmp(&orig, &regs, sizeof(orig)) != 0)
+		EXPECT_EQ(0, ARCH_SETREGS(regs));
 }
 
 void tracer_seccomp(struct __test_metadata *_metadata, pid_t tracee,