linux-kernel - Re: [PATCH] ARM: vdso: Mark vDSO code as read-only

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Message-ID: <20160217052010.GA49233@davidb.org>
Date:	Tue, 16 Feb 2016 22:20:10 -0700
From:	David Brown <david.brown@...aro.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Mathias Krause <minipli@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] ARM: vdso: Mark vDSO code as read-only

On Tue, Feb 16, 2016 at 01:52:33PM -0800, Kees Cook wrote:
>On Tue, Feb 16, 2016 at 1:36 PM, David Brown <david.brown@...aro.org> wrote:
>> Although the arm vDSO is cleanly separated by code/data with the code
>> being read-only in userspace mappings, the code page is still writable
>> from the kernel.  There have been exploits (such as
>> http://itszn.com/blog/?p=21) that take advantage of this on x86 to go
>> from a bad kernel write to full root.
>>
>> Prevent this specific exploit on arm by putting the vDSO code page in
>> post-init read-only memory as well.
>
>Is the vdso dynamically built at init time like on x86, or can this
>just use .rodata directly?

On ARM, it is patched during init.  Arm64's is just plain read-only.

David