Subject: Re: [PATCH 1/2] mm/kasan: dump alloc/free stack for page allocator

From: Walter Wu <[email-masked]>
Date: Wed, 4 Sep 2019 22:24:23 +0800

On Wed, 2019-09-04 at 16:13 +0200, Vlastimil Babka wrote:
> On 9/4/19 4:06 PM, Walter Wu wrote:
> > On Wed, 2019-09-04 at 14:49 +0200, Vlastimil Babka wrote:
> >> On 9/4/19 8:51 AM, Walter Wu wrote:
> >> > This patch is KASAN report adds the alloc/free stacks for page allocator
> >> > in order to help programmer to see memory corruption caused by page.
> >> > 
> >> > By default, KASAN doesn't record alloc/free stack for page allocator.
> >> > It is difficult to fix up page use-after-free issue.
> >> > 
> >> > This feature depends on page owner to record the last stack of pages.
> >> > It is very helpful for solving the page use-after-free or out-of-bound.
> >> > 
> >> > KASAN report will show the last stack of page, it may be:
> >> > a) If page is in-use state, then it prints alloc stack.
> >> >    It is useful to fix up page out-of-bound issue.
> >> 
> >> I expect this will conflict both in syntax and semantics with my series [1] that
> >> adds the freeing stack to page_owner when used together with debug_pagealloc,
> >> and it's now in mmotm. Glad others see the need as well :) Perhaps you could
> >> review the series, see if it fulfils your usecase (AFAICS the series should be a
> >> superset, by storing both stacks at once), and perhaps either make KASAN enable
> >> debug_pagealloc, or turn KASAN into an alternative enabler of the functionality
> >> there?
> >> 
> >> Thanks, Vlastimil
> >> 
> >> [1] https://lore.kernel.org/linux-mm/[email-masked]/t/#u
> >> 
> > Thanks your information.
> > We focus on the smartphone, so it doesn't enable
> > CONFIG_TRANSPARENT_HUGEPAGE, Is it invalid for our usecase?
> 
> The THP fix is not required for the rest of the series, it was even merged to
> mainline separately.
> 
> > And It looks like something is different, because we only need last
> > stack of page, so it can decrease memory overhead.
> 
> That would save you depot_stack_handle_t (which is u32) per page. I guess that's
> nothing compared to KASAN overhead?
> 
If we can use less memory, we can achieve what we want. Why not?

Thanks.
Walter

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