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

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

On 10 July 2018 at 19:57, James Morse <james.morse@....com> wrote:
> 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.
>

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@....com>
>

Thanks James