linux-hardening - Re: [PATCH] x86/vdso: Move vDSO to mmap region

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Date: Fri, 16 Feb 2024 21:31:01 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Daniel Micay <danielmicay@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Brian Gerst <brgerst@...il.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	"Chang S. Bae" <chang.seok.bae@...el.com>,
	Igor Zhbanov <i.zhbanov@...russia.ru>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Randy Dunlap <rdunlap@...radead.org>, linux-mm@...ck.org,
	John Allen <john.allen@....com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] x86/vdso: Move vDSO to mmap region

On Sat, Feb 10, 2024 at 01:18:35AM -0800, Kees Cook wrote:
> The vDSO (and its initial randomization) was introduced in commit
> 2aae950b21e4 ("x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu"),
> but had very low entropy. The entropy was improved in commit
> 394f56fe4801 ("x86_64, vdso: Fix the vdso address randomization algorithm"),
> but there is still improvement to be made.
> 
> On principle there should not be executable code at a low entropy offset
> from the stack, since the stack and executable code having separate
> randomization is part of what makes ASLR stronger.
> 
> Remove the only executable code near the stack region and give the vDSO
> the same randomized base as other mmap mappings including the linker
> and other shared objects. This results in higher entropy being provided
> and there's little to no advantage in separating this from the existing
> executable code there. This is already how other architectures like
> arm64 handle the vDSO.

Thread ping. Anyone have thoughts on this? I can carry it in -next to
see if anything melts...

-- 
Kees Cook