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Date: Fri, 26 Mar 2021 11:30:41 +0100
From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>,
 Andrew Cooper <andrew.cooper3@citrix.com>,
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Subject: Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate
 signal stack overflow
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On Thu, Mar 25, 2021 at 09:56:53PM -0700, Andy Lutomirski wrote:
> Nope.  on_sig_stack() is a horrible kludge and won't work here.  We
> could have something like __on_sig_stack() or sp_is_on_sig_stack() or
> something, though.

Yeah, see my other reply. Ack to either of those carved out helpers.

> I figure that the people whose programs spontaneously crash should get
> a hint why if they look at dmesg.  Maybe the message should say
> "overflowed sigaltstack -- try noavx512"?

I guess, as long as it is ratelimited. I mean, we can remove it later if
it starts gettin' annoying.

> We really ought to have a SIGSIGFAIL signal that's sent, double-fault
> style, when we fail to send a signal.

Yeap, we should be able to tell userspace that we couldn't send a
signal, hohumm.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette