linux-kernel - Re: Potential information leak in save_xstate

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Message-ID: <BC2CE4CC-744D-483D-B4B6-E37BFFF8D203@intel.com>
Date:   Mon, 6 Dec 2021 18:35:25 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Alexander Potapenko <glider@...gle.com>
CC:     Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        "Taras Madan" <tarasmadan@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Potential information leak in save_xstate_epilog()

On Nov 26, 2021, at 03:06, Alexander Potapenko <glider@...gle.com> wrote:
> 
> Hi Chang, Thomas, Borislav,
> 
> "x86/fpu/signal: Prepare for variable sigframe length" has presumably
> introduced an information leak to the userspace.
> 
> According to https://elixir.bootlin.com/linux/v5.16-rc2/source/arch/x86/kernel/fpu/signal.c#L126,
> save_sw_bytes() only initializes the first 20 bytes of sw_bytes, but
> then the whole struct is copied to the userspace.

Looks like your fix was picked already though, thank you for catching this!

Thanks,
Chang