Re: [PATCH] arm64/ptdump: Ensure memory hotplug is prevented during ptdump_check_wx()

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Jun 09, 2025 at 05:12:14AM +0100, Anshuman Khandual wrote:
> The arm64 page table dump code can race with concurrent modification of the
> kernel page tables. When a leaf entries are modified concurrently, the dump
> code may log stale or inconsistent information for a VA range, but this is
> otherwise not harmful.
> 
> When intermediate levels of table are freed, the dump code will continue to
> use memory which has been freed and potentially reallocated for another
> purpose. In such cases, the dump code may dereference bogus addresses,
> leading to a number of potential problems.
> 
> This problem was fixed for ptdump_show() earlier via commit 'bf2b59f60ee1
> ("arm64/mm: Hold memory hotplug lock while walking for kernel page table
> dump")' but a same was missed for ptdump_check_wx() which faced the race
> condition as well. Let's just take the memory hotplug lock while executing
> ptdump_check_wx().
> 
> Cc: stable@vger.kernel.org
> Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove")
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Reported-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>