linux-kernel - Re: [PATCH] tty: vt_ioctl: fix potential Spectre v1

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Date:   Fri, 17 Aug 2018 12:07:55 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: vt_ioctl: fix potential Spectre v1

On Thu, 16 Aug 2018 15:30:38 -0500
"Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote:

> vsa.console is indirectly controlled by user-space, hence leading to
> a potential exploitation of the Spectre variant 1 vulnerability.
> 
> This issue was detected with the help of Smatch:
> 
> drivers/tty/vt/vt_ioctl.c:711 vt_ioctl() warn: potential spectre issue
> 'vc_cons' [r]
> 
> Fix this by sanitizing vsa.console before using it to index vc_cons
> 
> Notice that given that speculation windows are large, the policy is
> to kill the speculation on the first load and not worry if it can be
> completed with a dependent load/store [1].
> 
> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Reviewed-by: Alan Cox <alan@...ux.intel.com>

Alan