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

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Message-ID: <20210325212733.GC32296@zn.tnic>
Date:   Thu, 25 Mar 2021 22:27:33 +0100
From:   Borislav Petkov <bp@...e.de>
To:     "Bae, Chang Seok" <chang.seok.bae@...el.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 Thu, Mar 25, 2021 at 09:11:56PM +0000, Bae, Chang Seok wrote:
> But if sigaltstack()’ed with the SS_AUTODISARM flag, both on_sig_stack() and
> sas_ss_flags() return 0 [1]. Then, segfault always here. v5 had the exact
> issue before [2].

Ah, there's that SS_AUTODISARM check above it which I missed, sorry.

I guess we can do a __on_sig_stack() helper or so which does the stack
check only without the SS_AUTODISARM. Just for readability's sake in
what is already a pretty messy function.

Thx.

-- 
Regards/Gruss,
    Boris.

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