Messages in this thread | | | Date | Sun, 8 May 2022 21:17:01 +0300 | Subject | Re: [PATCH v2 03/13] stackleak: remove redundant check | From | Alexander Popov <> |
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On 27.04.2022 20:31, Mark Rutland wrote: > In __stackleak_erase() we check that the `erase_low` value derived from > `current->lowest_stack` is above the lowest legitimate stack pointer > value, but this is already enforced by stackleak_track_stack() when > recording the lowest stack value. > > Remove the redundant check. > > There should be no functional change as a result of this patch.
Mark, I can't agree here. I think this check is important. The performance profit from dropping it is less than the confidence decrease :)
With this check, if the 'lowest_stack' value is corrupted, stackleak doesn't overwrite some wrong kernel memory, but simply clears the whole thread stack, which is safe behavior.
> Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Alexander Popov <alex.popov@linux.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Kees Cook <keescook@chromium.org> > --- > kernel/stackleak.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/kernel/stackleak.c b/kernel/stackleak.c > index 753eab797a04d..f7a0f8cf73c37 100644 > --- a/kernel/stackleak.c > +++ b/kernel/stackleak.c > @@ -78,10 +78,6 @@ static __always_inline void __stackleak_erase(void) > unsigned int poison_count = 0; > const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long); > > - /* Check that 'lowest_stack' value is sane */ > - if (unlikely(kstack_ptr - boundary >= THREAD_SIZE)) > - kstack_ptr = boundary; > - > /* Search for the poison value in the kernel stack */ > while (kstack_ptr > boundary && poison_count <= depth) { > if (*(unsigned long *)kstack_ptr == STACKLEAK_POISON)
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