linux-kernel - Re: [PATCH] x86/efi-bgrt: remove the check of the version field

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Date:	Mon, 15 Aug 2016 13:56:43 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Icenowy Zheng <icenowy@...c.xyz>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Josh Triplett <josh@...htriplett.org>,
	Dave Young <dyoung@...hat.com>,
	Josh Boyer <jwboyer@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH] x86/efi-bgrt: remove the check of the version field

On Tue, 09 Aug, at 01:25:46PM, Icenowy Zheng wrote:
> Some broken firmwares have a wrongly filled version field in BGRT table.
> (See http://wiki.osdev.org/Broken_UEFI_implementations )
> 
> As we know, these firmwares can also provide correct BGRT image, although
> the table is wrong.
> 
> After removing the check of the version field, the kernel can now extract
> the image correctly, and the information is also correct.
> 
> Tested on a Thinkpad E531 (68854UC).
> 
> Signed-off-by: Icenowy Zheng <icenowy@...c.xyz>
> ---
>  arch/x86/platform/efi/efi-bgrt.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
> index 6a2f569..f492ea0 100644
> --- a/arch/x86/platform/efi/efi-bgrt.c
> +++ b/arch/x86/platform/efi/efi-bgrt.c
> @@ -47,11 +47,6 @@ void __init efi_bgrt_init(void)
>  		       bgrt_tab->header.length, sizeof(*bgrt_tab));
>  		return;
>  	}
> -	if (bgrt_tab->version != 1) {
> -		pr_notice("Ignoring BGRT: invalid version %u (expected 1)\n",
> -		       bgrt_tab->version);
> -		return;
> -	}
>  	if (bgrt_tab->status & 0xfe) {
>  		pr_notice("Ignoring BGRT: reserved status bits are non-zero %u\n",
>  		       bgrt_tab->status);

This would be less scary if we checked for known broken and known good
version values instead of removing the check altogether, i.e. 0 and 1.

The whole point of the version field is that it tells us about the
layout of the BGRT table, so it's not exactly a useless check.