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Date: Wed, 7 Oct 2020 11:20:16 +0100
From: Dave Martin <Dave.Martin@arm.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>, "Chang S. Bae" <chang.seok.bae@intel.com>,
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Subject: Re: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size
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On Tue, Oct 06, 2020 at 11:30:42AM -0700, Dave Hansen wrote:
> On 10/6/20 10:00 AM, Dave Martin wrote:
> > On Tue, Oct 06, 2020 at 08:33:47AM -0700, Dave Hansen wrote:
> >> On 10/6/20 8:25 AM, Dave Martin wrote:
> >>> Or are people reporting real stack overruns on x86 today?
> >> We have real overruns.  We have ~2800 bytes of XSAVE (regisiter) state
> >> mostly from AVX-512, and a 2048 byte MINSIGSTKSZ.
> > Right.  Out of interest, do you believe that's a direct consequence of
> > the larger kernel-generated signal frame, or does the expansion of
> > userspace stack frames play a role too?
> 
> The kernel-generated signal frame is entirely responsible for the ~2800
> bytes that I'm talking about.
> 
> I'm sure there are some systems where userspace plays a role, but those
> are much less of a worry at the moment, since the kernel-induced
> overflows mean an instant crash that userspace has no recourse for.

Ack, that sounds pretty convincing.

Cheers
---Dave