Re: [PATCH 1/5] efi/memattr: Fix thinko in table size sanity check

[Gregory Price <gourry@gourry.net>]

On Thu, Mar 26, 2026 at 02:26:57PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> While it is true that each PE/COFF runtime driver in memory can
> generally be split into 3 different regions (the header, the code/rodata
> region and the data/bss region), each with different permissions, it
> does not mean that 3x the size of the memory map is a suitable upper
> bound. This is due to the fact that all runtime drivers could be
> coalesced into a single EFI runtime code region by the firmware, and if
> the firmware does a good job of keeping the fragmentation down, it is
> conceivable that the memory attributes table has more entries than the
> EFI memory map itself.
> 
> So instead, base the sanity check on whether the descriptor size matches
> the EFI memory map's descriptor size (which is not mandated by the spec
> but extremely unlikely to differ in practice), and whether the size of
> the whole table does not exceed 2 MiB.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

The 2MB limit is a bit odd to me - but then i don't see a legitimate
reason to need 50k+ entries here unless the system is doing something
absolutely nutty - it would mean a wildly fragmented system and most
likely an indicator of a bug rather than a legitimately intended
configuration.

Otherwise, this does seem like a better check regardless.

Reviewed-by: Gregory Price <gourry@gourry.net>