linux-kernel - Re: [PATCH] efi/x86: Memory protection on EfiGcdMemoryTypeMoreReliable

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Message-ID: <CAMj1kXHbtLY_H2J_z=sRO1Yyt5fOJ-aS+ErQEXrbwL+qw5mG+w@mail.gmail.com>
Date: Mon, 29 Sep 2025 17:14:35 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Lenny Szubowicz <lszubowi@...hat.com>
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi/x86: Memory protection on EfiGcdMemoryTypeMoreReliable

On Tue, 16 Sept 2025 at 21:39, Lenny Szubowicz <lszubowi@...hat.com> wrote:
>
> Check for needed memory protection changes on EFI DXE GCD memory space
> descriptors with type EfiGcdMemoryTypeMoreReliable in addition to
> EfiGcdMemoryTypeSystemMemory.
>
> This fixes a fault on entry into the decompressed kernel from the
> EFI stub that occurs when the memory allocated for the decompressed
> kernel is more reliable memory, has NX/XP set, and the kernel needs
> to use the EFI DXE protocol to adjust memory protections.
>
> The memory descriptors returned by the DXE protocol
> GetMemorySpaceDescriptor() service use a different GCD memory type
> to distinguish more reliable memory ranges from their conventional
> counterparts. This is in contrast to the EFI memory descriptors
> returned by the EFI GetMemoryMap() service which use the
> EFI_MEMORY_MORE_RELIABLE memory attributes flag to identify
> EFI_CONVENTIONAL_MEMORY type regions that have this additional
> property.
>
> Signed-off-by: Lenny Szubowicz <lszubowi@...hat.com>

Queued up now, thanks.

> ---
>  drivers/firmware/efi/libstub/x86-stub.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> index cafc90d4caaf..0f60a12401c2 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -300,7 +300,7 @@ efi_status_t efi_adjust_memory_range_protection(unsigned long start,
>                 return EFI_SUCCESS;
>
>         /*
> -        * Don't modify memory region attributes, they are
> +        * Don't modify memory region attributes, if they are
>          * already suitable, to lower the possibility to
>          * encounter firmware bugs.
>          */
> @@ -315,11 +315,13 @@ efi_status_t efi_adjust_memory_range_protection(unsigned long start,
>                 next = desc.base_address + desc.length;
>
>                 /*
> -                * Only system memory is suitable for trampoline/kernel image placement,
> -                * so only this type of memory needs its attributes to be modified.
> +                * Only system memory and more reliable memory are suitable for
> +                * trampoline/kernel image placement. So only those memory types
> +                * may need to have attributes modified.
>                  */
>
> -               if (desc.gcd_memory_type != EfiGcdMemoryTypeSystemMemory ||
> +               if ((desc.gcd_memory_type != EfiGcdMemoryTypeSystemMemory &&
> +                    desc.gcd_memory_type != EfiGcdMemoryTypeMoreReliable) ||
>                     (desc.attributes & (EFI_MEMORY_RO | EFI_MEMORY_XP)) == 0)
>                         continue;
>
> --
> 2.51.0
>
>