linux-kernel - Re: [PATCH] efi: Check EFI revision in setup_efi

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Date:	Wed, 24 Apr 2013 15:44:30 +0100
From:	Matt Fleming <matt.fleming@...el.com>
To:	Josh Boyer <jwboyer@...hat.com>
CC:	Matthew Garrett <matthew.garrett@...ula.com>,
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: Check EFI revision in setup_efi_vars

On 24/04/13 15:37, Josh Boyer wrote:
> We need to check the runtime sys_table for the EFI version the firmware
> specifies instead of just checking for a NULL QueryVariableInfo.  Older
> implementations of EFI don't have QueryVariableInfo but the runtime is
> a smaller structure, so the pointer to it may be pointing off into garbage.
> 
> This is apparently the case with several Apple firmwares that support EFI
> 1.10, and the current check causes them to no longer boot.  Fix based on
> a suggestion from Matthew Garrett.
> 
> Signed-off-by: Josh Boyer <jwboyer@...hat.com>
> ---
>  arch/x86/boot/compressed/eboot.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> index 8615f75..b46efbf 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -258,7 +258,9 @@ static efi_status_t setup_efi_vars(struct boot_params *params)
>  	u64 store_size, remaining_size, var_size;
>  	efi_status_t status;
>  
> -	if (!sys_table->runtime->query_variable_info)
> +	if (sys_table->runtime->hdr.revision < EFI_2_00_SYSTEM_TABLE_REVISION)
> +		return EFI_UNSUPPORTED;
> +	else if(!sys_table->runtime->query_variable_info)
>  		return EFI_UNSUPPORTED;
>  
>  	data = (struct setup_data *)(unsigned long)params->hdr.setup_data;
> 

Thanks Josh, that looks correct.

It's a small point, but does the check against NULL actually make sense?
I don't think we ever check other system table pointers against NULL.
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