Date: Wed, 17 Feb 2016 16:43:06 -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 Wed, Feb 17, 2016 at 03:00:52PM -0800, Kees Cook wrote: >On Tue, Feb 16, 2016 at 9:20 PM, David Brown <david.brown@...aro.org> 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 <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. > >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? David
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