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