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Date: Wed, 17 Feb 2016 16:43:06 -0700
From: David Brown <>
To: Kees Cook <>
Cc: Russell King <>,
	"" <>,
	"" <>,
	Ingo Molnar <>,
	Andy Lutomirski <>,
	"H. Peter Anvin" <>,
	Michael Ellerman <>,
	Mathias Krause <>,
	Thomas Gleixner <>,
	"" <>, Arnd Bergmann <>,
	PaX Team <>, Emese Revfy <>,
	LKML <>,
	linux-arch <>
Subject: Re: [PATCH] ARM: vdso: Mark vDSO code as read-only

On Wed, Feb 17, 2016 at 03:00:52PM -0800, Kees Cook wrote:
>On Tue, Feb 16, 2016 at 9:20 PM, David Brown <> wrote:
>> On Tue, Feb 16, 2016 at 01:52:33PM -0800, Kees Cook wrote:
>>> On Tue, Feb 16, 2016 at 1:36 PM, David Brown <>
>>> 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
>>>> 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.
>Okay, great. I've added this to my postinit-readonly series (which I
>just refreshed and sent out again...)

However, this distinction between .rodata and .data..ro_after_init is
kind of fuzzy, anyway, since they both get made actually read-only at
the same time (post init).  The patch actually does work fine with the
vDSO page in .rodata, since the patching happens during init.

Is there a possible future consideration to perhaps make .rodata read
only much earlier?


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