Re: [PATCH v2 2/2] x86/efi: Apply EFI Memory Attributes after kexec

[Nicolas Saenz Julienne <nsaenz@amazon.com>]

On Fri Nov 15, 2024 at 4:39 PM UTC, Ard Biesheuvel wrote:
> On Tue, 12 Nov 2024 at 19:53, Nicolas Saenz Julienne <nsaenz@amazon.com> wrote:
>>
>> Kexec bypasses EFI's switch to virtual mode. In exchange, it has its own
>> routine, kexec_enter_virtual_mode(), which replays the mappings made by
>> the original kernel. Unfortunately, that function fails to reinstate
>> EFI's memory attributes, which would've otherwise been set after
>> entering virtual mode. Remediate this by calling
>> efi_runtime_update_mappings() within kexec's routine.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: 18141e89a76c ("x86/efi: Add support for EFI_MEMORY_ATTRIBUTES_TABLE")
>> Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
>>
>> ---
>>
>> Notes:
>> - Tested with QEMU/OVMF.
>>
>
>
> I'll queue these up,

Thanks!

> but I am going drop the cc stable: the memory attributes table is an
> overlay of the EFI memory map with restricted permissions for EFI
> runtime services regions, which are only mapped while a EFI runtime
> call is in progress.
>
> So if the table is not taken into account after kexec, the runtime
> code and data mappings will all be RWX but I think this is a situation
> we can live with. If nothing breaks, we can always revisit this later
> if there is an actual need.

My intention was backporting the fix all the way to
'stable/linux-5.10.y'. But I'm happy to wait, or even to maintain an
internal backport. It's simple enough.

Nicolas