From 8caa016bfc129f2c925d52da43022171d1d1de91 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 20 Nov 2019 12:59:13 -0800 Subject: [PATCH] selftests/x86/mov_ss_trap: Fix the SYSENTER test For reasons that I haven't quite fully diagnosed, running mov_ss_trap_32 on a 32-bit kernel results in an infinite loop in userspace. This appears to be because the hacky SYSENTER test doesn't segfault as desired; instead it corrupts the program state such that it infinite loops. Fix it by explicitly clearing EBP before doing SYSENTER. This will give a more reliable segfault. Fixes: 59c2a7226fc5 ("x86/selftests: Add mov_to_ss test") Signed-off-by: Andy Lutomirski Signed-off-by: Peter Zijlstra (Intel) Cc: stable@kernel.org --- tools/testing/selftests/x86/mov_ss_trap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/x86/mov_ss_trap.c b/tools/testing/selftests/x86/mov_ss_trap.c index 3c3a0226..6da0ac3 100644 --- a/tools/testing/selftests/x86/mov_ss_trap.c +++ b/tools/testing/selftests/x86/mov_ss_trap.c @@ -257,7 +257,8 @@ int main() err(1, "sigaltstack"); sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND | SA_ONSTACK); nr = SYS_getpid; - asm volatile ("mov %[ss], %%ss; SYSENTER" : "+a" (nr) + /* Clear EBP first to make sure we segfault cleanly. */ + asm volatile ("xorl %%ebp, %%ebp; mov %[ss], %%ss; SYSENTER" : "+a" (nr) : [ss] "m" (ss) : "flags", "rcx" #ifdef __x86_64__ , "r11" -- 2.7.4