linux-kernel - Re: [PATCH v3 3/4] x86/signal: Prevent an alternate stack overflow before a signal delivery

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Message-ID: <20210108180935.GB12995@zn.tnic>
Date:   Fri, 8 Jan 2021 19:09:35 +0100
From:   Borislav Petkov <bp@...e.de>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>
Cc:     tglx@...utronix.de, mingo@...nel.org, luto@...nel.org,
        x86@...nel.org, len.brown@...el.com, dave.hansen@...el.com,
        hjl.tools@...il.com, Dave.Martin@....com, jannh@...gle.com,
        mpe@...erman.id.au, tony.luck@...el.com, ravi.v.shankar@...el.com,
        libc-alpha@...rceware.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/4] x86/signal: Prevent an alternate stack overflow
 before a signal delivery

On Tue, Dec 22, 2020 at 05:53:11PM -0800, 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.
^^^^^^^^^^^^^^^^^^^^^^^

Formulate properly.

> 
> When the kernel knows that the user stack is too small, avoid the overflow
> and do an immediate SIGSEGV instead.
      ^^^^^^^^^^^^^^^^^^^^^^^

Ditto.

> This overflow is known to occur on systems with large XSAVE state. The
> effort to increase the size typically used for altstacks reduces the
						^^^^^^^^^^

"alternate signal stacks"

-- 
Regards/Gruss,
    Boris.

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