linux-kernel - Re: [PATCH] firmware: google: memconsole: Prevent overrun attack on coreboot console

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Message-ID: <20170520083223.GB3460@kroah.com>
Date:   Sat, 20 May 2017 10:32:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Julius Werner <jwerner@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Aaron Durbin <adurbin@...omium.org>
Subject: Re: [PATCH] firmware: google: memconsole: Prevent overrun attack on
 coreboot console

On Fri, May 19, 2017 at 02:44:38PM -0700, Julius Werner wrote:
> The recent coreboot memory console update (firmware: google: memconsole:
> Adapt to new coreboot ring buffer format) introduced a small security
> issue in the driver: The new driver implementation parses the memory
> console structure again on every access. This is intentional so that
> additional lines added concurrently by runtime firmware can be read out.
> 
> However, if an attacker can write to the structure, they could increase
> the size value to a point where the driver would read potentially
> sensitive memory areas from outside the original console buffer during
> the next access. This can be done through /dev/mem, since the console
> buffer usually resides in firmware-reserved memory that is not covered
> by STRICT_DEVMEM.
> 
> This patch resolves that problem by reading the buffer's size value only
> once during boot (where we can still trust the structure). Other parts
> of the structure can still be modified at runtime, but the driver's
> bounds checks make sure that it will never read outside the buffer.
> 
> Signed-off-by: Julius Werner <jwerner@...omium.org>

Care to provide a "Fixes: SHA" type line here saying what commit this
fixes the issue for, to allow people to know what is going on.

thanks,

greg k-h