linux-kernel - Re: [PATCH v2 1/3] arm64: mm: Don't sleep in split_kernel_leaf

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <de2f65f0-8b5d-4d64-a918-4f0c91ee3e59@gmail.com>
Date: Thu, 6 Nov 2025 22:08:14 +0100
From: "David Hildenbrand (Red Hat)" <davidhildenbrandkernel@...il.com>
To: Ryan Roberts <ryan.roberts@....com>, catalin.marinas@....com,
 will@...nel.org, yang@...amperecomputing.com, ardb@...nel.org,
 dev.jain@....com, scott@...amperecomputing.com, cl@...two.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Guenter Roeck <groeck@...gle.com>
Subject: Re: [PATCH v2 1/3] arm64: mm: Don't sleep in
 split_kernel_leaf_mapping() when in atomic context

On 06.11.25 17:09, Ryan Roberts wrote:
> It has been reported that split_kernel_leaf_mapping() is trying to sleep
> in non-sleepable context. It does this when acquiring the
> pgtable_split_lock mutex, when either CONFIG_DEBUG_PAGEALLOC or
> CONFIG_KFENCE are enabled, which change linear map permissions within
> softirq context during memory allocation and/or freeing. All other paths
> into this function are called from sleepable context and so are safe.
> 
> But it turns out that the memory for which these 2 features may attempt
> to modify the permissions is always mapped by pte, so there is no need
> to attempt to split the mapping. So let's exit early in these cases and
> avoid attempting to take the mutex.
> 
> There is one wrinkle to this approach; late-initialized kfence allocates
> it's pool from the buddy which may be block mapped. So we must hook that
> allocation and convert it to pte-mappings up front. Previously this was
> done as a side-effect of kfence protecting all the individual pages in
> its pool at init-time, but this no longer works due to the added early
> exit path in split_kernel_leaf_mapping().
> 
> So instead, do this via the existing arch_kfence_init_pool() arch hook,
> and reuse the existing linear_map_split_to_ptes() infrastructure.
> 
> Closes: https://lore.kernel.org/all/f24b9032-0ec9-47b1-8b95-c0eeac7a31c5@roeck-us.net/
> Fixes: a166563e7ec3 ("arm64: mm: support large block mapping when rodata=full")
> Tested-by: Guenter Roeck <groeck@...gle.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---

Reviewed-by: David Hildenbrand (Red Hat) <david@...nel.org>