On Tue, May 20, 2025 at 05:13:28PM +0800, Coiby Xu wrote:
On Mon, May 19, 2025 at 10:34:39PM +0800, Baoquan He wrote:
On 05/19/25 at 07:19am, Kees Cook wrote:
On Mon, May 19, 2025 at 09:22:30AM +0800, Baoquan He wrote:
[...]
> I went back through the thread and the referenced threads and I can't
> find any details on the USBAN splat. Can that please get reproduced in a
> commit log? That would help understand if it's a false positive or not.
The original patch is trying to fix a potential issue in which a memory
range is split, while the sub-range split out is always on top of the
entire memory range, hence no risk.
Later, we encountered a UBSAN warning around the above memory range
splitting code several times. We found this patch can mute the warning.
Please see below UBSAN splat trace report from Coiby:
https://lore.kernel.org/all/4de3c2onosr7negqnfhekm4cpbklzmsimgdfv33c52dktqpza5@z5pb34ghz4at/T/#u
Ah-ha! Thanks for the link.
Later, Coiby got the root cause from investigation, please see:
https://lore.kernel.org/all/2754f4evjfumjqome63bc3inqb7ozepemejn2lcl57ryio2t6k@35l3tnn73gei/T/#u
Looking at https://lore.kernel.org/all/aBxfflkkQXTetmbq@MiWiFi-R3L-srv/
it seems like this actually turned out to be a legitimate overflow
detection? I.e. the fix isn't silencing a false positive, but rather
allocating enough space?
The words "out of bounds" in the patch subject are kind of misleading
because the patch is outdated. A later merged commit 6dff31597264
("crash_core: fix and simplify the logic of crash_exclude_mem_range()")
has actually fixed out-of-bound access issue as illustrated in
https://lore.kernel.org/kexec/ZXrY7QbXAlxydsSC@MiWiFi-R3L-srv/ Current
crash_exclude_mem_range simply returns -ENOMEM when there is no
enough space to hold split ranges (I'll post a patch to prove the
correctness of crash_exclude_mem_range by reasoning about the code and
including a thorough unit tests). So I'll change the subject to "fix
potential cmem->ranges out of memory" in the upcoming patch.
The kdump LUKS support patches which fix the UBSAN warnings as a
byproduct are now in the Andrew's mm-nonmm-stable tree. Can I assume
it's not appropriate to re-send a new version of kdump LUKS support
patches which includes a separate patch to fix the UBSAN warnings alone?
If that's the case, I can send a single patch to the stable tree if the
stable tree requires an upstream commit already in Linus's tree.
--
Best regards,
Coiby
