Re: [tip:x86/boot] x86/boot: Make memcpy() handle overlaps

[Kees Cook]

On Fri, Apr 22, 2016 at 2:05 PM, Lasse Collin <lasse.collin@xxxxxxxxxxx> wrote:
> On 2016-04-22 tip-bot for Kees Cook wrote:
>> x86/boot: Make memcpy() handle overlaps
>>
>> Two uses of memcpy() (screen scrolling and ELF parsing) were handling
>> overlapping memory areas. While there were no explicitly noticed bugs
>> here (yet), it is best to fix this so that the copying will always be
>> safe.
>>
>> Instead of making a new memmove() function that might collide with
>> other memmove() definitions in the decompressors, this just makes the
>> compressed boot code's copy of memcpy() overlap-safe.
>
> So far lib/decompress_unxz.c is the only decompressor that needs
> memmove(). There the local definition is inside #ifndef to make it easy
> to omit it and to use another memmove() implementation. It's enough to
> do this:
>
>     #define memmove memmove
>
> To me it sounds less confusing if a function that works on overlapping
> buffers is named memmove() instead of memcpy(). In those places where
> buffers can overlap one would then use memmove() so that it's clear to
> the reader that overlapping is possible.

Okay, I'll refactor this and double-check the xz case.

Thanks!

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security