Re: [patch V4 part 1 08/36] x86/doublefault: Remove memmove() call

Alexandre Chartre
2020-05-06T13:49:22Z

On 5/5/20 3:16 PM, Thomas Gleixner wrote:
> Use of memmove() in #DF is problematic considered tracing and other
> instrumentation.
>
> Remove the memmove() call and simply write out what needs doing; this
> even clarifies the code, win-win! The code copies from the espfix64
> stack to the normal task stack, there is no possible way for that to
> overlap.
>
> Survives selftests/x86, specifically sigreturn_64.
>
> Suggested-by: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Acked-by: Andy Lutomirski <luto@kernel.org>
> Link: https://lkml.kernel.org/r/20200220121727.GB507@zn.tnic
> ---
> arch/x86/kernel/traps.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)

Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

alex.

> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -278,6 +278,7 @@ dotraplinkage void do_double_fault(struc
> regs->ip == (unsigned long)native_irq_return_iret)
> {
> struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
> + unsigned long *p = (unsigned long *)regs->sp;
>
> /*
> * regs->sp points to the failing IRET frame on the
> @@ -285,7 +286,11 @@ dotraplinkage void do_double_fault(struc
> * in gpregs->ss through gpregs->ip.
> *
> */
> - memmove(&gpregs->ip, (void *)regs->sp, 5*8);
> + gpregs->ip = p[0];
> + gpregs->cs = p[1];
> + gpregs->flags = p[2];
> + gpregs->sp = p[3];
> + gpregs->ss = p[4];
> gpregs->orig_ax = 0; /* Missing (lost) #GP error code */
>
> /*
>