From: Matthew Wilcox <willy@infradead.org>
To: Audra Mitchell <audra@redhat.com>
Cc: linux-mm@kvack.org, raquini@redhat.com, aris@redhat.com,
akpm@linux-foundation.org, william.kucharski@oracle.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: Stop PMD alignment for PIE shared objects
Date: Thu, 19 Dec 2024 21:30:58 +0000 [thread overview]
Message-ID: <Z2SQkrldCVDiTeia@casper.infradead.org> (raw)
In-Reply-To: <20241219211552.1450226-1-audra@redhat.com>
On Thu, Dec 19, 2024 at 04:15:52PM -0500, Audra Mitchell wrote:
> After commit 1854bc6e2420 ("mm/readahead: Align file mappings for non-DAX")
> any request through thp_get_unmapped_area would align to a PMD_SIZE,
> causing shared objects to have less randomization than previously (9 less
> bits for 2MB PMDs). As these lower 9 bits are the most impactful for
> ASLR, this change could be argued to have an impact on security.
Yes, very tiresome people have been making that argument for a long
time. Do you have anything further to add to the discussion that
happened here:
https://lore.kernel.org/linux-mm/20240118133504.2910955-1-shy828301@gmail.com/
particularly in light of 3afb76a66b55 existing.
> Fix this issue by checking that the request is aligned to the PMD_SIZE,
> otherwise fall back to mm_get_unmapped_area_vmflags().
NAK this version anyway. Even if the executable is, say, 2.1MB in size,
we still want the first 2MB of the file to be covered with a PMD
mapping.
next prev parent reply other threads:[~2024-12-19 21:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-19 21:15 Audra Mitchell
2024-12-19 21:30 ` Matthew Wilcox [this message]
2024-12-19 21:59 ` Audra Mitchell
2024-12-20 18:20 ` Rafael Aquini
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