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

Masami Hiramatsu
2020-05-11T12:28:25Z

On Tue, 05 May 2020 15:43:55 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:

> 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>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you,

> ---
> 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)
>

--
Masami Hiramatsu <mhiramat@kernel.org>