[PATCH] x86: profiling: Using generic unwinding in profile_pc

[Chen Zhongjin]

Syzbot has been reporting the problem of stack-out-of-bounds in
profile_pc for a long time:
https://syzkaller.appspot.com/bug?extid=84fe685c02cd112a2ac3

profile_pc tries to get pc if current regs is inside lock function. For
!CONFIG_FRAME_POINTER it used a hack way to get the pc from stack, which
is not work with ORC. It makes profile_pc returns wrong result, and
frequently triggers KASAN.

This can be fixed by using the unwind_start, it will skip the first
regs frame and get the caller of lock function directly, or 0 if
unwind_get_return_address finds the unwinding failed. For all of FP, ORC
and guess unwinders it works.

Fixes: 0cb91a229364 ("[PATCH] i386: Account spinlocks to the caller during profiling for !FP kernels")
Reported-by: syzbot+84fe685c02cd112a2ac3@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
---
 arch/x86/kernel/time.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
index e42faa792c07..5e0446f49906 100644
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -24,26 +24,18 @@
 #include <asm/timer.h>
 #include <asm/hpet.h>
 #include <asm/time.h>
+#include <asm/unwind.h>
 
 unsigned long profile_pc(struct pt_regs *regs)
 {
 	unsigned long pc = instruction_pointer(regs);
 
 	if (!user_mode(regs) && in_lock_functions(pc)) {
-#ifdef CONFIG_FRAME_POINTER
-		return *(unsigned long *)(regs->bp + sizeof(long));
-#else
-		unsigned long *sp = (unsigned long *)regs->sp;
-		/*
-		 * Return address is either directly at stack pointer
-		 * or above a saved flags. Eflags has bits 22-31 zero,
-		 * kernel addresses don't.
-		 */
-		if (sp[0] >> 22)
-			return sp[0];
-		if (sp[1] >> 22)
-			return sp[1];
-#endif
+		struct unwind_state state;
+
+		/* unwind_start will skip the first regs frame */
+		unwind_start(&state, current, regs, NULL);
+		pc = unwind_get_return_address(&state);
 	}
 	return pc;
 }
-- 
2.17.1