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Date:   Tue, 6 Oct 2020 18:00:21 +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>,
        Thomas Gleixner <tglx@linutronix.de>,
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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 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?

In practice software just assumes SIGSTKSZ and then ignores the problem
until / unless an actual stack overflow is seen.

There's probably a lot of software out there whose stack is
theoretically too small even without AVX-512 etc. in the mix, especially
when considering the possibility of nested signals...

Cheers
---Dave