[patch V4 part 3 01/29] x86/traps: Mark fixup_bad_iret() noinstr

Thomas Gleixner
2020-05-05T14:21:55Z

This is called from deep entry ASM in a situation where instrumentation
will cause more harm than providing useful information.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/traps.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -621,7 +621,7 @@ struct bad_iret_stack {
struct pt_regs regs;
};

-asmlinkage __visible notrace
+asmlinkage __visible noinstr
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
{
/*
@@ -632,19 +632,21 @@ struct bad_iret_stack *fixup_bad_iret(st
* just below the IRET frame) and we want to pretend that the
* exception came from the IRET target.
*/
- struct bad_iret_stack *new_stack =
- (struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+ struct bad_iret_stack tmp, *new_stack =
+ (struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;

- /* Copy the IRET target to the new stack. */
- memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+ /* Copy the IRET target to the temporary storage. */
+ memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);

/* Copy the remainder of the stack from the current stack. */
- memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+ memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+
+ /* Update the entry stack */
+ memcpy(new_stack, &tmp, sizeof(tmp));

BUG_ON(!user_mode(&new_stack->regs));
return new_stack;
}
-NOKPROBE_SYMBOL(fixup_bad_iret);
#endif

static bool is_sysenter_singlestep(struct pt_regs *regs)