Re: [PATCH] efi: Override runtime supported mask from a EFI variable if present

From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] efi: Override runtime supported mask from a EFI variable if present
Date: Thu, 10 Nov 2022 14:37:03 +0000	[thread overview]
Message-ID: <Y20MjzkbX+yM/A0G@monolith.localdoman> (raw)
In-Reply-To: <20221109172750.2823891-1-ardb@kernel.org>

Hi,

On Wed, Nov 09, 2022 at 06:27:50PM +0100, Ard Biesheuvel wrote:
> For debugging purposes, allow the runtime override mask to be set from a
> EFI variable if one exists. For instance, the RT supported mask can be
> set to 0xfffd to disable the SetTime() runtime service, and enable all
> others:
> 
>   echo -ne "\x7\0\0\0\xfd\xff" \
>     > /sys/firmware/efi/efivars/LinuxRtMaskOverride-eb66918a-7eef-402a-842e-931d21c38ae9

I'm really sorry, I applied this patch, but I couldn't find the file
(LinuxRtMaskOverride*) under efivars, and couldn't find another way of
setting the variable.

Thanks,
Alex

> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  drivers/firmware/efi/efi.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index a46df5d1d0942751..faed1ef78c044924 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -367,7 +367,17 @@ static int __init efisubsys_init(void)
>  		}
>  	}
>  
> -	if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES))
> +	if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
> +		unsigned long size = sizeof(efi.runtime_supported_mask);
> +
> +		if (efi.get_variable(L"LinuxRtMaskOverride",
> +				     &EFI_RT_PROPERTIES_TABLE_GUID, NULL, &size,
> +				     &efi.runtime_supported_mask) == EFI_SUCCESS)
> +			pr_info("Overriding runtime_supported_mask to 0x%x\n",
> +				efi.runtime_supported_mask);
> +	}
> +
> +	if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_TIME))
>  		platform_device_register_simple("rtc-efi", 0, NULL, 0);
>  
>  	/* We register the efi directory at /sys/firmware/efi */
> -- 
> 2.35.1
> 

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