linux-kernel - Re: [PATCH v3.1 2/4] efi/arm: preserve early mapping of UEFI memory map longer for BGRT

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Date:   Tue, 10 Jul 2018 18:57:31 +0100
From:   James Morse <james.morse@....com>
To:     ard.biesheuvel@...aro.org
Cc:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        catalin.marinas@....com, will.deacon@....com,
        tbaicar@...eaurora.org, bhsharma@...hat.com, dyoung@...hat.com,
        mark.rutland@....com, al.stone@...aro.org,
        graeme.gregory@...aro.org, hanjun.guo@...aro.org,
        lorenzo.pieralisi@....com, sudeep.holla@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v3.1 2/4] efi/arm: preserve early mapping of UEFI memory
 map longer for BGRT

Hi Ard,

On 10/07/18 00:42, AKASHI Takahiro wrote:
> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> 
> The BGRT code validates the contents of the table against the UEFI
> memory map, and so it expects it to be mapped when the code runs.
> 
> On ARM, this is currently not the case, since we tear down the early
> mapping after efi_init() completes, and only create the permanent
> mapping in arm_enable_runtime_services(), which executes as an early
> initcall, but still leaves a window where the UEFI memory map is not
> mapped.
> 
> So move the call to efi_memmap_unmap() from efi_init() to
> arm_enable_runtime_services().

I don't have a machine that generates a BGRT, but I can see that efi_mem_type()
call in efi_bgrt_init() would cause the same problems we have with kexec and acpi.


> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
> index b5214c143fee..388a929baf95 100644
> --- a/drivers/firmware/efi/arm-init.c
> +++ b/drivers/firmware/efi/arm-init.c
> @@ -259,7 +259,6 @@ void __init efi_init(void)
>  
>  	reserve_regions();
>  	efi_esrt_init();
> -	efi_memmap_unmap();
>  
>  	memblock_reserve(params.mmap & PAGE_MASK,
>  			 PAGE_ALIGN(params.mmap_size +
> diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
> index 5889cbea60b8..59a8c0ec94d5 100644
> --- a/drivers/firmware/efi/arm-runtime.c
> +++ b/drivers/firmware/efi/arm-runtime.c
> @@ -115,6 +115,8 @@ static int __init arm_enable_runtime_services(void)
>  		return 0;
>  	}
>  
> +	efi_memmap_unmap();

This can get called twice if uefi_init() fails after setting the EFI_BOOT flag,
but this can only happen if the system table signature is wrong, (or we're out
of memory really early).

I think this is harmless as we end up passing NULL to early_memunmap() which
WARN()s and returns as its outside the fixmap range. Its just more noise on
systems with a corrupt efi system table.

Acked-by: James Morse <james.morse@....com>


Thanks,

James