[RFC,v1,2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

Commit Message

Ammar Faizi Jan. 24, 2023, 12:26 a.m. UTC

From: Ammar Faizi <[e-mail]>

Test that:

 - "syscall" in a FRED system doesn't clobber %rcx and %r11.
 - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.

Test them out with a trivial system call like __NR_getppid and friends
which are extremely likely to return with SYSRET on an IDT system; check
that it returns a nonnegative value and then save the result.

Link: https://lore.kernel.org/lkml/[e-mail]
Co-developed-by: "H. Peter Anvin" <[e-mail]>
Signed-off-by: Ammar Faizi <[e-mail]>
---

Missing a Signed-off-by tag from HPA. 

@hpa send your sign off if you like this patch.

 tools/testing/selftests/x86/sysret_rip.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c
index 9056f2e2674d2bc5..c55f6d04f0ae1f2d 100644
--- a/tools/testing/selftests/x86/sysret_rip.c
+++ b/tools/testing/selftests/x86/sysret_rip.c
@@ -252,8 +252,17 @@  static void test_syscall_fallthrough_to(unsigned long ip)
 	printf("[OK]\tWe survived\n");
 }
 
+static void test_syscall_rcx_r11(void)
+{
+	do_syscall(__NR_getpid, 0, 0, 0, 0, 0, 0);
+	do_syscall(__NR_gettid, 0, 0, 0, 0, 0, 0);
+	do_syscall(__NR_getppid, 0, 0, 0, 0, 0, 0);
+}
+
 int main()
 {
+	test_syscall_rcx_r11();
+
 	/*
 	 * When the kernel returns from a slow-path syscall, it will
 	 * detect whether SYSRET is appropriate.  If it incorrectly