From: Mike Rapoport <rppt@kernel.org>
To: Rik van Riel <riel@surriel.com>
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 08:00:47 +0300 [thread overview]
Message-ID: <20230720050047.GL1901145@kernel.org> (raw)
In-Reply-To: <20230719154137.732d8525@imladris.surriel.com>
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.
> 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.
> Avoid those issues by making sure that memblock_discard points
> memblock.reserved.regions back at the static buffer.
>
> If memblock_discard is called while there is still memory
> in the memblock.reserved type, that will print a warning
> in memblock_remove_region.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
> mm/memblock.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 3feafea06ab2..068289a46903 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -374,6 +374,10 @@ void __init memblock_discard(void)
> kfree(memblock.reserved.regions);
> else
> memblock_free_late(addr, size);
> + /* Reset to prevent UAF from stray frees. */
> + memblock.reserved.regions = memblock_reserved_init_regions;
> + memblock.reserved.cnt = 1;
> + memblock_remove_region(&memblock.reserved, 0);
> }
>
> if (memblock.memory.regions != memblock_memory_init_regions) {
> --
> 2.34.1
>
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2023-07-20 5:01 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-19 19:41 [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF Rik van Riel
2023-07-20 5:00 ` Mike Rapoport [this message]
2023-07-20 13:15 ` Rik van Riel
2023-07-20 16:25 ` Mike Rapoport
2023-07-28 16:09 ` Guenter Roeck
2023-07-28 16:36 ` Guenter Roeck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20230720050047.GL1901145@kernel.org \
--to=rppt@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=kernel-team@meta.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=riel@surriel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).