[PATCH] i386/x86-64: Add user_mode checks to profile_pc for oprofile

Fixes a obscure user space triggerable crash during oprofiling.

Oprofile calls profile_pc from NMIs even when user_mode(regs) is not true and
the program counter is inside the kernel lock section. This opens
a race - when a user program jumps to a kernel lock address and
a NMI happens before the illegal page fault exception is raised
and the program has a unmapped esp or ebp then the kernel could
oops. NMIs have a higher priority than exceptions so that could
happen.

Add user_mode checks to i386/x86-64 profile_pc to prevent that.

Cc: John Levon <[e-mail]>
Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/time.c

···
 {
 	unsigned long pc = instruction_pointer(regs);
 
-	if (in_lock_functions(pc))
+	if (!user_mode_vm(regs) && in_lock_functions(pc))
 		return *(unsigned long *)(regs->ebp + 4);
 
 	return pc;

arch/x86_64/kernel/time.c

···
 	   is just accounted to the spinlock function.
 	   Better would be to write these functions in assembler again
 	   and check exactly. */
-	if (in_lock_functions(pc)) {
+	if (!user_mode(regs) && in_lock_functions(pc)) {
 		char *v = *(char **)regs->rsp;
 		if ((v >= _stext && v <= _etext) ||
 			(v >= _sinittext && v <= _einittext) ||