From: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> 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/25b96960-a07e-a952-5c23-786b55054126@xxxxxxxxx Co-developed-by: "H. Peter Anvin" <hpa@xxxxxxxxx> Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> --- Need hpa's sign off. tools/testing/selftests/x86/sysret_rip.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c index 550bc4e69ac46997..75c72d34dbc5840c 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 -- Ammar Faizi
