Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime

From	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime
Date	2015-09-09 12:10 +0200
Message-ID	<q6Kud-8mm-9@gated-at.bofh.it> (permalink)
References	(4 earlier) <q6qYA-5iH-37@gated-at.bofh.it> <q6r8e-5u9-11@gated-at.bofh.it> <q6xQm-6JP-7@gated-at.bofh.it> <q6I93-4QA-7@gated-at.bofh.it> <q6Kky-7VO-9@gated-at.bofh.it>
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On 9 September 2015 at 11:58, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> On Wed, 09 Sep, at 09:37:21AM, Ard Biesheuvel wrote:
>> On 8 September 2015 at 22:37, Matt Fleming <matt@codeblueprint.co.uk> wrote:
>> >
>> > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
>> > index 691b333e0038..a2af35f6093a 100644
>> > --- a/arch/x86/platform/efi/efi.c
>> > +++ b/arch/x86/platform/efi/efi.c
>> > @@ -704,6 +704,44 @@ out:
>> >         return ret;
>> >  }
>> >
>> > +static inline void *efi_map_next_entry_reverse(void *entry)
>> > +{
>> > +       if (!entry)
>> > +               return memmap.map_end - memmap.desc_size;
>> > +
>> > +       entry -= memmap.desc_size;
>> > +       if (entry < memmap.map)
>> > +               return NULL;
>> > +
>> > +       return entry;
>> > +}
>> > +
>> > +static void *efi_map_next_entry(void *entry)
>> > +{
>> > +       bool reverse = false;
>> > +
>> > +       if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) {
>>
>> Here, you could also test whether the
>> EFI_PROPERTIES_RUNTIME_MEMORY_PROTECTION_NON_EXECUTABLE_PE_DATA bit
>> (sigh) is set
>
> No, leaving this out was intentional because we're already suffering
> from the combinatoral explosion of config options. Introducing more
> code paths is very much the wrong thing to do unless absolutely
> necessary.
>
> If we can get away with using one mapping scheme here, we should.
>
> When trying to debug this code in the future I do not want to be
> thinking "Do you have EFI_PROPERTIES_RUNTIME_OMG_THIS_IS_SILLY bit
> set? because that means we're mapping the runtime regions in a
> different order".
>

OK, point taken. I suppose buggy firmware already has the option of
using EFI_OLD_MEMMAP as a fallback.

-- 
Ard.
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Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-08 15:20 +0200
  Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-08 15:30 +0200
    Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-08 22:40 +0200
      Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-09 09:40 +0200
        Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Matt Fleming <matt@codeblueprint.co.uk> - 2015-09-09 12:00 +0200
          Re: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-09-09 12:10 +0200

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