linux-kernel - Re: [PATCH 4/4] efi: Skip parsing of EFI_PROPERTIES_TABLE if EFI_MEMORY_ATTRIBUTES

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Date:   Wed, 7 Dec 2016 13:36:45 +0000
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        jlee@...e.com, bp@...en8.de, ricardo.neri@...el.com,
        ard.biesheuvel@...aro.org, ravi.v.shankar@...el.com,
        fenghua.yu@...el.com
Subject: Re: [PATCH 4/4] efi: Skip parsing of EFI_PROPERTIES_TABLE if
 EFI_MEMORY_ATTRIBUTES_TABLE is detected

On Tue, 06 Dec, at 11:16:03AM, Sai Praneeth Prakhya wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@...el.com>
> 
> UEFI specification v2.6 recommends not to use
> "EFI_PROPERTIES_RUNTIME_MEMORY_PROTECTION_NON_EXECUTABLE_PE_DATA"
> attribute of EFI_PROPERTIES_TABLE. Presently, this is the *only* bit
> defined in EFI_PROPERTIES_TABLE. This bit implies that EFI Runtime code
> and data regions of an executable image are separate and are aligned as
> specified in spec. Please refer to "EFI_PROPERTIES_TABLE" in section 4.6
> of UEFI specification v2.6 for more information on this table.
> 
> UEFI v2.6 introduces EFI_MEMORY_ATTRIBUTES_TABLE and is intended to
> replace EFI_PROPERTIES_TABLE. If EFI_MEMORY_ATTRIBUTES_TABLE is found we
> skip updating of efi runtime region mappings based on
> EFI_PROPERTIES_TABLE, so let's also skip parsing of EFI_PROPERTIES_TABLE
> if we find EFI_MEMORY_ATTRIBUTES_TABLE because we are not using this
> table anyways. The only caveat here is, if further versions of UEFI spec
> adds some more bits (hence some more attributes) to EFI_PROPERTIES_TABLE
> then we might need to parse it again, otherwise there is no good in
> doing that. We can also expect that the same attributes might be reflected in
> EFI_MEMORY_ATTRIBUTES_TABLE and hence saving us from parsing
> EFI_PROPERTIES_TABLE again.
> 
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> Cc: Lee, Chun-Yi <jlee@...e.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Ricardo Neri <ricardo.neri@...el.com>
> Cc: Matt Fleming <matt@...eblueprint.co.uk>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Ravi Shankar <ravi.v.shankar@...el.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  drivers/firmware/efi/efi.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

I see where you're coming from with this patch, but I think it's
unnecessary. Turning on/off parsing of Table A based on existence of
Table B just seems like extra work.