linux-kernel - Re: [PATCH v2] mm: mmap: allow for the maximum number of bits for randomizing mmap

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Date: Mon, 10 Jun 2024 11:11:39 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Rafael Aquini <aquini@...hat.com>
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>, Heiko
 Carstens <hca@...ux.ibm.com>, Petr Mladek <pmladek@...e.com>, Mike Rapoport
 <rppt@...nel.org>, Paul McKenney <paulmck@...nel.org>, Samuel Holland
 <samuel.holland@...ive.com>
Subject: Re: [PATCH v2] mm: mmap: allow for the maximum number of bits for
 randomizing mmap_base by default

On Thu,  6 Jun 2024 14:06:22 -0400 Rafael Aquini <aquini@...hat.com> wrote:

> An ASLR regression was noticed [1] and tracked down to file-mapped areas
> being backed by THP in recent kernels. The 21-bit alignment constraint
> for such mappings reduces the entropy for randomizing the placement of
> 64-bit library mappings and breaks ASLR completely for 32-bit libraries.
> 
> The reported issue is easily addressed by increasing vm.mmap_rnd_bits
> and vm.mmap_rnd_compat_bits. This patch just provides a simple way to
> set ARCH_MMAP_RND_BITS and ARCH_MMAP_RND_COMPAT_BITS to their maximum
> values allowed by the architecture at build time.
> 
> [1] https://zolutal.github.io/aslrnt/

Are we able to identify a Fixes: target for this?

I assume a cc:stable is appropriate?