From: Rik van Riel <riel@surriel.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF
Date: Thu, 20 Jul 2023 09:15:25 -0400 [thread overview]
Message-ID: <7dc943023c620bed4bf49710dbe6facaade203fa.camel@surriel.com> (raw)
In-Reply-To: <20230720050047.GL1901145@kernel.org>
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On Thu, 2023-07-20 at 08:00 +0300, Mike Rapoport wrote:
> Hi Ric,
>
> On Wed, Jul 19, 2023 at 03:41:37PM -0400, Rik van Riel wrote:
> > The memblock_discard function frees the memblock.reserved.regions
> > array, which is good.
> >
> > However, if a subsequent memblock_free (or memblock_phys_free)
> > comes
> > in later, from for example ima_free_kexec_buffer, that will result
> > in
> > a use after free bug in memblock_isolate_range.
>
> The use of memblock_phys_free() in ima_free_kexec_buffer() is
> entirely
> bogus and must be fixed. It should be memblock_free_late() there.
>
I'll send in a patch for that code, then. Thank you!
> > When running a kernel with CONFIG_KASAN enabled, this will cause a
> > kernel panic very early in boot. Without CONFIG_KASAN, there is
> > a chance that memblock_isolate_range might scribble on memory
> > that is now in use by somebody else.
>
> This can't happen because memblock_double_array() uses kmalloc() as
> soon as
> slab_is_available(), so this sentence is misleading.
memblock_discard() freed the array, but did not change
the pointer. That resulted in memblock_isolate_range()
following a stale pointer.
There was no call to memblock_double_array() in the
final call that crashed. I checked that by booting
with memblock=debug.
kind regards,
Rik van Riel
--
All Rights Reversed.
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next prev parent reply other threads:[~2023-07-20 13:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-19 19:41 Rik van Riel
2023-07-20 5:00 ` Mike Rapoport
2023-07-20 13:15 ` Rik van Riel [this message]
2023-07-20 16:25 ` Mike Rapoport
2023-07-28 16:09 ` Guenter Roeck
2023-07-28 16:36 ` Guenter Roeck
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