linux-kernel - Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if CONFIG_JUMP

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Date:	Wed, 2 Apr 2014 01:21:01 +0200
From:	Rabin Vincent <rabin@....in>
To:	Kees Cook <keescook@...omium.org>
Cc:	Laura Abbott <lauraa@...eaurora.org>,
	Alexander Holler <holler@...oftware.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if
 CONFIG_JUMP_LABEL is enabled

2014-04-01 20:36 GMT+02:00 Kees Cook <keescook@...omium.org>:
> On Tue, Apr 1, 2014 at 11:03 AM, Laura Abbott <lauraa@...eaurora.org> wrote:
>> On 4/1/2014 3:04 AM, Alexander Holler wrote:
>>> CONFIG_DEBUG_SET_MODULE_RONX sounds like a nice security feature, but
>>> things might fail late (and unexpected) if module code is set to read-only
>>> while CONFIG_JUMP_LABEL is enabled (e.g. modprobe bridge).
>
> Isn't this a ordering problem? I thought jump labels got set up once,
> and then after that, the memory could be made RO?

The code gets patched every time the jump label is enabled/disabled,
i.e. every time the static_key is turned on/off based on
static_key_slow_{inc/dec}()
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