Re: [PATCH v5 0/3] Implement fast refcount overflow protection

[Kees Cook]

On Wed, May 31, 2017 at 5:27 AM, Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
> On Tue, 30 May 2017, Kees Cook wrote:
>
>> A new patch has been added at the start of this series to make the default
>> refcount_t implementation just use an unchecked atomic_t implementation,
>> since many kernel subsystems want to be able to opt out of the full
>> validation, since it includes a small performance overhead. When enabling
>> CONFIG_REFCOUNT_FULL, the full validation is used.
>>
>> The other two patches provide overflow protection on x86 without incurring
>> a performance penalty. The changelog for patch 3 is reproduced here for
>> details:
>
>
> To be sure I'm getting this right, after this all archs with the exception
> of x86 will use the regular atomic_t ("unsecure") flavor, right?

If a build does not select CONFIG_REFCOUNT_FULL and lacks
CONFIG_ARCH_HAS_REFCOUNT, refcount_t will be the same at atomic_t
(i.e. no change from the historical behavior where all the ref
counters in the kernel used atomic_t).

-Kees

-- 
Kees Cook
Pixel Security