Re: Wanted: simple, safe x86 stack overflow detection
- From: Andi Kleen <andi@xxxxxxxxxxxxxx>
- Date: Wed, 28 Feb 2007 21:41:44 +0100
On Wed, Feb 28, 2007 at 09:27:09AM -0500, Chuck Ebbert wrote:
Can we just put a canary in the threadinfo and check it on every
task switch? What are the drawbacks?
Likely already too late then -- if critical state is overwritten
you crashed before. Also a lot of stack intensive codes
relatively large unused holes so it might miss the canary completely
Anyways if you want a crash on context switch in the non
hole case you can probably get it by just rearranging thread_info a bit.
e.g. put preempt_count first. Any corruption of that will lead
to schedule complaining.
Don't think it is worth it though.
I suppose one could have a CONFIG_DEBUG_STACK_OVERFLOW that gets
the stacks from vmalloc which would catch any overflow with its
guard pages. This is you would need to change __pa() to handle
that too because there might be still some drivers that do
DMA on stack addresses. Would be somewhat ugly but doable.
But I have my doubts it is worth it again -- in my experience static
analysis works well enough to trace them down and
there are not that many anyways.
-Andi
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- References:
- Wanted: simple, safe x86 stack overflow detection
- From: Chuck Ebbert
- Wanted: simple, safe x86 stack overflow detection
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