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Date:   Wed, 23 Dec 2020 07:55:20 +0100
From:   Jann Horn <>
To:     "Chang S. Bae" <>
Cc:     Borislav Petkov <>, Thomas Gleixner <>,
        Ingo Molnar <>,
        Andy Lutomirski <>,
        "the arch/x86 maintainers" <>,
        Len Brown <>,
        Dave Hansen <>,
        "H.J. Lu" <>, Dave Martin <>,
        Michael Ellerman <>,
        Tony Luck <>,
        "Ravi V. Shankar" <>,, linux-arch <>,
        Linux API <>,
        kernel list <>
Subject: Re: [PATCH v3 3/4] x86/signal: Prevent an alternate stack overflow
 before a signal delivery

On Wed, Dec 23, 2020 at 2:57 AM Chang S. Bae <> wrote:
> The kernel pushes data on the userspace stack when entering a signal. If
> using a sigaltstack(), the kernel precisely knows the user stack size.
> When the kernel knows that the user stack is too small, avoid the overflow
> and do an immediate SIGSEGV instead.
> This overflow is known to occur on systems with large XSAVE state. The
> effort to increase the size typically used for altstacks reduces the
> frequency of these overflows, but this approach is still useful for legacy
> binaries.
> Suggested-by: Jann Horn <>
> Signed-off-by: Chang S. Bae <>
> Reviewed-by: Len Brown <>
> Cc: Jann Horn <>
> Cc:
> Cc:

Reviewed-by: Jann Horn <>

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