On Thu, Jan 11, 2018 at 2:24 AM, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxx> wrote:
> On Wed, Jan 10, 2018 at 06:03:06PM -0800, Kees Cook wrote:
>> ARM does not carry FPU state in the thread structure, so it can declare
>> no usercopy whitelist at all.
>
> This comment seems to be misleading. We have stored FP state in the
> thread structure for a long time - for example, VFP state is stored
> in thread->vfpstate.hard, so we _do_ have floating point state in
> the thread structure.
>
> What I think this commit message needs to describe is why we don't
> need a whitelist _despite_ having FP state in the thread structure.
>
> At the moment, the commit message is making me think that this patch
> is wrong and will introduce a regression.
Yeah, I will improve this comment; it's not clear enough. The places
where I see state copied to/from userspace are all either static sizes
or already use bounce buffers (or both). e.g.:
err |= __copy_from_user(&hwstate->fpregs, &ufp->fpregs,
sizeof(hwstate->fpregs));
I will adjust the commit log and comment to more clearly describe the
lack of whitelisting due to all-static sized copies.
Thanks!
-Kees
--
Kees Cook
Pixel Security
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