[v1] x86/efi: Re-enable memory attributes table for kexec

[PATCH 0/5] x86/efi: Re-enable memory attributes table for kexec

Posted by Ard Biesheuvel 1 week ago

From: Ard Biesheuvel <ardb@kernel.org>

The EFI memory attributes table augments the EFI memory map, and
provides permission attributes for all runtime code and data regions
that are otherwise mapped read-write-execute in their entirety.

Currently, this table is disregarded when doing kexec boot on x86, for
two reasons:
- the boot services data region that holds the table is not reserved
  correctly, and may contain garbage at kexec time
- a misguided sanity check on the size of the table is likely to trigger
  on kexec, as the EFI memory map has been trimmed down by that time.

Fix both issues, so that the EFI memory attributes table can be taken
into account again at kexec time. Note that this requires that the call
to efi_memattr_init() is moved to a later point for x86.

Cc: Dave Young <dyoung@redhat.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Breno Leitao <leitao@debian.org>

Ard Biesheuvel (5):
  efi/memattr: Fix thinko in table size sanity check
  x86/efi: Gather initial memory reservation and table handling logic
  x86/efi: Defer the call to efi_memattr_init()
  efi: Use efi_mem_reserve() to reserve the memory attribute table
  x86/efi: Drop kexec quirk for the EFI memory attributes table

 arch/x86/include/asm/efi.h     |  5 ++---
 arch/x86/kernel/setup.c        | 11 ++---------
 arch/x86/platform/efi/efi.c    | 15 +++++++++++++++
 arch/x86/platform/efi/quirks.c |  4 ----
 drivers/firmware/efi/efi.c     |  2 +-
 drivers/firmware/efi/memattr.c | 17 ++++++++++-------
 6 files changed, 30 insertions(+), 24 deletions(-)


base-commit: 217c0a5c177a3d4f7c8497950cbf5c36756e8bbb
-- 
2.53.0.1018.g2bb0e51243-goog

Re: [PATCH 0/5] x86/efi: Re-enable memory attributes table for kexec

Posted by Dave Young 3 days, 8 hours ago

On Thu, 26 Mar 2026 at 21:27, Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> The EFI memory attributes table augments the EFI memory map, and
> provides permission attributes for all runtime code and data regions
> that are otherwise mapped read-write-execute in their entirety.
>
> Currently, this table is disregarded when doing kexec boot on x86, for
> two reasons:
> - the boot services data region that holds the table is not reserved
>   correctly, and may contain garbage at kexec time
> - a misguided sanity check on the size of the table is likely to trigger
>   on kexec, as the EFI memory map has been trimmed down by that time.
>
> Fix both issues, so that the EFI memory attributes table can be taken
> into account again at kexec time. Note that this requires that the call
> to efi_memattr_init() is moved to a later point for x86.

I vaguely remember when we discussed this issue in old threads
efi_mem_reserve can not work for kexec_load syscall, but I think after
the commit a2498e5c453b it should just work.   So I think it looks
good, thanks Ard!

Thanks
Dave

Re: [PATCH 0/5] x86/efi: Re-enable memory attributes table for kexec

Posted by Gregory Price 4 days, 1 hour ago

On Thu, Mar 26, 2026 at 02:26:56PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> The EFI memory attributes table augments the EFI memory map, and
> provides permission attributes for all runtime code and data regions
> that are otherwise mapped read-write-execute in their entirety.
> 
> Currently, this table is disregarded when doing kexec boot on x86, for
> two reasons:
> - the boot services data region that holds the table is not reserved
>   correctly, and may contain garbage at kexec time
> - a misguided sanity check on the size of the table is likely to trigger
>   on kexec, as the EFI memory map has been trimmed down by that time.
> 
> Fix both issues, so that the EFI memory attributes table can be taken
> into account again at kexec time. Note that this requires that the call
> to efi_memattr_init() is moved to a later point for x86.
> 

I appreciate this fixup, I'll try to give it a test in some known host
configuration switch scenarios I know don't work across multiple kexecs
and see if it is an improvement.

~Gregory

> Cc: Dave Young <dyoung@redhat.com>
> Cc: Gregory Price <gourry@gourry.net>
> Cc: Usama Arif <usamaarif642@gmail.com>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: Breno Leitao <leitao@debian.org>
> 
> Ard Biesheuvel (5):
>   efi/memattr: Fix thinko in table size sanity check
>   x86/efi: Gather initial memory reservation and table handling logic
>   x86/efi: Defer the call to efi_memattr_init()
>   efi: Use efi_mem_reserve() to reserve the memory attribute table
>   x86/efi: Drop kexec quirk for the EFI memory attributes table
> 
>  arch/x86/include/asm/efi.h     |  5 ++---
>  arch/x86/kernel/setup.c        | 11 ++---------
>  arch/x86/platform/efi/efi.c    | 15 +++++++++++++++
>  arch/x86/platform/efi/quirks.c |  4 ----
>  drivers/firmware/efi/efi.c     |  2 +-
>  drivers/firmware/efi/memattr.c | 17 ++++++++++-------
>  6 files changed, 30 insertions(+), 24 deletions(-)
> 
> 
> base-commit: 217c0a5c177a3d4f7c8497950cbf5c36756e8bbb
> -- 
> 2.53.0.1018.g2bb0e51243-goog
>