linux-kernel - Re: [Xen-devel] [PATCH] [v2] xen: hypercall: fix out-of-bounds memcpy

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Date:   Mon, 5 Feb 2018 15:14:29 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
CC:     <xen-devel@...ts.xenproject.org>,
        David Laight <David.Laight@...lab.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] [v2] xen: hypercall: fix out-of-bounds memcpy

On 05/02/18 15:03, Arnd Bergmann wrote:

Snipping deleted code to make things clearer:

> +	if (cmd > ARRAY_SIZE(physdevop_len))
> +		return -ENOSYS;
>
> +	len = physdevop_len[cmd];
> +	memcpy(&op.u, arg, len);

You'll want an array_nospec() or whatever its called these days.  This
code is SP1-leaky.

Userspace controls cmd and can retrieve len by timing how many adjacent
cache lines were pulled in my memcpy().

~Andrew