linux-kernel - Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit

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Message-ID: <2d7bd8b2b9736d4a7d0a26169978372b5e002a62.camel@debian.org>
Date: Thu, 11 Jul 2024 22:10:12 +0200
From: Yves-Alexis Perez <corsac@...ian.org>
To: Yang Shi <shy828301@...il.com>, jirislaby@...nel.org, surenb@...gle.com,
  riel@...riel.com, willy@...radead.org, cl@...ux.com,
 akpm@...ux-foundation.org
Cc: yang@...amperecomputing.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Salvatore Bonaccorso <carnil@...ian.org>, Ben
 Hutchings <ben@...adent.org.uk>
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32
 bit

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On Thu, 2024-01-18 at 05:35 -0800, Yang Shi wrote:
> The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
> boundaries") caused two issues [1] [2] reported on 32 bit system or compat
> userspace.
> 
> It doesn't make too much sense to force huge page alignment on 32 bit
> system due to the constrained virtual address space.

Hi people,

sorry for beeing so late. I've looked at this following the OpenSSH issue
(CVE-2024-6387 [1]) and especially the impact on IA-32 installations where
ASLR is apparently broken.

There was a recent thread [2] on oss-security discussing the issue.

Looking at the commit log I think the intention was to fix this both for:
- - 32 bit process running on 64 bit kernels: in_compat_syscall()
- - all processes running on 32 bit kernels: IS_ENABLED(CONFIG_32BIT)

Unfortunately, as far as I can tell, CONFIG_32BIT is not enabled on 32bit x86
kernels. Maybe CONFIG_X86_32 would be the right one there?

[1] https://www.openwall.com/lists/oss-security/2024/07/01/3
[2] https://www.openwall.com/lists/oss-security/2024/07/08/3
- -- 
Yves-Alexis
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