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

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To: Andy Lutomirski <luto@xxxxxxxxxx>
Subject: Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Thu, 25 Mar 2021 21:58:54 -0700
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, X86 ML <x86@xxxxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxx>, "H. J. Lu" <hjl.tools@xxxxxxxxx>, Dave Martin <Dave.Martin@xxxxxxx>, Jann Horn <jannh@xxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, "Carlos O'Donell" <carlos@xxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>, libc-alpha <libc-alpha@xxxxxxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, Linux API <linux-api@xxxxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, "Bae, Chang Seok" <chang.seok.bae@xxxxxxxxx>
In-reply-to: <CALCETrU_n+dP4GaUJRQoKcDSwaWL9Vc99Yy+N=QGVZ_tx_j3Zg@mail.gmail.com>
References: <20210316065215.23768-1-chang.seok.bae@intel.com> <20210316065215.23768-6-chang.seok.bae@intel.com> <CALCETrU_n+dP4GaUJRQoKcDSwaWL9Vc99Yy+N=QGVZ_tx_j3Zg@mail.gmail.com>

I forgot to mention why I cc'd all you fine Xen folk:

On Thu, Mar 25, 2021 at 11:13 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote:

>
> >         } else if (IS_ENABLED(CONFIG_X86_32) &&
> >                    !onsigstack &&
> >                    regs->ss != __USER_DS &&

This bit here seems really dubious on Xen PV.  Honestly it seems
dubious everywhere, but especially on Xen PV.

--Andy

References:
- [PATCH v7 0/6] x86: Improve Minimum Alternate Stack Size
  - From: Chang S. Bae
- [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow
  - From: Chang S. Bae
- Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow
  - From: Andy Lutomirski

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