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

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: James Morse <james.morse@arm.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	"Baicar, Tyler" <tbaicar@codeaurora.org>,
	Bhupesh Sharma <bhsharma@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Al Stone <al.stone@linaro.org>,
	Graeme Gregory <graeme.gregory@linaro.org>,
	Hanjun Guo <hanjun.guo@linaro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Kexec Mailing List <kexec@lists.infradead.org>
Subject: Re: [PATCH v3.1 2/4] efi/arm: preserve early mapping of UEFI memory map longer for BGRT
Date: Tue, 10 Jul 2018 20:39:16 +0200	[thread overview]
Message-ID: <CAKv+Gu_fajf3_P0wKpdV34Ungu=fn0=WG1U_MSQ9WF_2GFRfDA@mail.gmail.com> (raw)
In-Reply-To: <93c42065-bece-a4c7-ed99-5e98f91315a6@arm.com>

On 10 July 2018 at 19:57, James Morse <james.morse@arm.com> wrote:
> Hi Ard,
>
> On 10/07/18 00:42, AKASHI Takahiro wrote:
>> From: Ard Biesheuvel <ard.biesheuvel@linaro.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.
>

I'm not sure I follow. The BGRT table only contains natively aligned
fields, so the alignment faults should not occur when accessing this
table after kexec. The issue addressed by this patch is that
efi_mem_type() bails when called while EFI_MEMMAP is cleared.

>
>> 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 guess we should check the EFI_MEMMAP attribute here as well then.

> 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@arm.com>
>

Thanks James