linux-kernel - Re: Potential information leak in save_xstate

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Message-ID: <87fsrhfiqr.ffs@tglx>
Date:   Sat, 27 Nov 2021 21:26:04 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexander Potapenko <glider@...gle.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...e.de>
Cc:     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 Fri, Nov 26 2021 at 12:06, Alexander Potapenko 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.

Yes, that clearly lacks a memset(0).

Thanks,

        tglx