linux-kernel - Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow

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Message-ID: <20210414101250.GD10709@zn.tnic>
Date:   Wed, 14 Apr 2021 12:12:50 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Florian Weimer <fweimer@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "Cooper, Andrew" <andrew.cooper3@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "Gross, Jurgen" <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Jann Horn <jannh@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Carlos O'Donell <carlos@...hat.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        libc-alpha <libc-alpha@...rceware.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate
 signal stack overflow

On Mon, Apr 12, 2021 at 10:30:23PM +0000, Bae, Chang Seok wrote:
> On Mar 26, 2021, at 03:30, Borislav Petkov <bp@...en8.de> wrote:
> > On Thu, Mar 25, 2021 at 09:56:53PM -0700, Andy Lutomirski wrote:
> >> 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.
> 
> Hi Boris,
> 
> Let me clarify some details as preparing to include this in a revision.
> 
> So, IIUC, a number needs to be assigned for this new SIGFAIL. At a glance, not
> sure which one to pick there in signal.h -- 1-31 fully occupied and the rest
> for 33 different real-time signals.
> 
> Also, perhaps, force_sig(SIGFAIL) here, instead of return -1 -- to die with
> SIGSEGV.

I think this needs to be decided together with userspace people so that
they can act accordingly and whether it even makes sense to them.

Florian, any suggestions?

Subthread starts here:

https://lkml.kernel.org/r/CALCETrXQZuvJQrHDMst6PPgtJxaS_sPk2JhwMiMDNPunq45YFg@mail.gmail.com

Thx.

-- 
Regards/Gruss,
    Boris.

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