[PATCH v4 2/3] initmem: introduce CONFIG_INIT_ALL_HEAP

[Alexander Potapenko]

On Wed, Apr 10, 2019 at 6:09 PM Kees Cook <keescook at chromium.org> wrote:
>
> On Wed, Apr 10, 2019 at 6:18 AM Alexander Potapenko <glider at google.com> wrote:
> >
> > This config option adds the possibility to initialize newly allocated
> > pages and heap objects with a 0xAA pattern.
> > There's already a number of places where allocations are initialized
> > based on the presence of __GFP_ZERO flag. We just change this code so
> > that under CONFIG_INIT_ALL_HEAP these allocations are always initialized
> > with either 0x00 or 0xAA depending on the __GFP_ZERO.
>
> Why not just make __GFP_ZERO unconditional instead? This looks like
> it'd be simpler and not need arch-specific implementation?
Right, but it would mean we can only initialize with 0x00 pattern.
I believe that for testing purposes a nonzero pattern is better,
because it'll not only assure the execution is deterministic, but will
also uncover logic bugs earlier (see the discussion at
https://reviews.llvm.org/D54604?id=174471)
For hardening purposes the pattern shouldn't matter much.

If you think arch-specific code is too much of a trouble, we could
implement clear_page_pattern() using memset() on every architecture,
but allow the user to choose between slow (0xAA) and production (0x00)
modes.
> --
> Kees Cook



-- 
Alexander Potapenko
Software Engineer

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