linux-kernel - Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery

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Message-ID: <CA+8MBb+M5JoDGONxZuMHZb8VU4DmG=zsv_0JuBhnzn6T=eSKEA@mail.gmail.com>
Date:   Fri, 20 Aug 2021 21:51:41 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Jue Wang <juew@...gle.com>, Ding Hui <dinghui@...gfor.com.cn>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Oscar Salvador <osalvador@...e.de>,
        Youquan Song <youquan.song@...el.com>, huangcun@...gfor.com.cn,
        X86-ML <x86@...nel.org>,
        Linux Edac Mailing List <linux-edac@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery

On Fri, Aug 20, 2021 at 1:25 PM Luck, Tony <tony.luck@...el.com> wrote:
> Probably the same for the two different addresses case ... though I'm
> not 100% confident about that. There could be some ioctl() that peeks
> at two parts of a passed in structure, and the user might pass in a
> structure that spans across a page boundary with both pages poisoned.
> But that would only hit if the driver code ignored the failure of the
> first get_user() and blindly tried the second. So I'd count that as a
> critically bad driver bug.

Or maybe driver writers are just evil :-(

for (i = 0; i < len; i++) {
       tx_wait(10);
       get_user(dsp56k_host_interface.data.b[1], bin++);
       get_user(dsp56k_host_interface.data.b[2], bin++);
       get_user(dsp56k_host_interface.data.b[3], bin++);
}

-Tony