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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>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, X86 ML <x86@kernel.org>,
        Len Brown <len.brown@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        "H. J. Lu" <hjl.tools@gmail.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Jann Horn <jannh@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Carlos O'Donell <carlos@redhat.com>,
        Tony Luck <tony.luck@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        libc-alpha <libc-alpha@sourceware.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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