linux-kernel - Re: [PATCH 4.4 07/40] arm64: ensure __dump_instr() checks addr

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Date:   Mon, 13 Nov 2017 19:05:12 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH 4.4 07/40] arm64: ensure __dump_instr() checks addr_limit

On Mon, 2017-11-06 at 10:44 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Mark Rutland <mark.rutland@....com>
> 
> commit 7a7003b1da010d2b0d1dc8bf21c10f5c73b389f1 upstream.
> 
> It's possible for a user to deliberately trigger __dump_instr with a
> chosen kernel address.
> 
> Let's avoid problems resulting from this by using get_user() rather than
> __get_user(), ensuring that we don't erroneously access kernel memory.
> 
> Where we use __dump_instr() on kernel text, we already switch to
> KERNEL_DS, so this shouldn't adversely affect those cases.
> 
> Fixes: 60ffc30d5652810d ("arm64: Exception handling")
[...]

This seems harmless, but I don't think it will fix the bug in 4.4
unless you also cherry-pick:

commit c5cea06be060f38e5400d796e61cfc8c36e52924
Author: Mark Rutland <mark.rutland@....com>
Date:   Mon Jun 13 11:15:14 2016 +0100

    arm64: fix dump_instr when PAN and UAO are in use

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.