On Fri, 2013-03-15 at 10:21 -0700, Linus Torvalds wrote:
> Adding linux-arch. Guys, can you check your architectures?
>
> Also, make sure to check huge-pages if they are separate. Basically,
> if you have code like this:
>
> if (!pte_present(pte) ||
> pte_special(pte) || (write && !pte_write(pte))) {
> pte_unmap(ptep);
> return 0;
> }
>
> it's probably buggy. It's not sufficient to just check write
> permissions, you do need to check user permissions too.
>
> Powerpc,x86 and sh seem to get it right by virtue of checking rthe
> user bit. s390 checks against TASK_SIZE.
>
> MIPS does seem buggy. Sparc I don't know the meaning of the bits for.
> And powerpc does have several variants, so while the main one looks
> fine, I didn't look at the other ones.
Took the train half way through... I assume we are talking gup_fast
here ? So we have an access_ok() accross the range, which should make
us safe. Additionally on ppc64 we have a different pgd for user and
kernel pages anyway.
We do check for huge pages at every level as far as I can tell (and
those are user only) and finally we check for _PAGE_USER.
The only "subtlety" I can think of is that PROT_NONE has no _PAGE_USER
for us and thus will fail a gup but that's expected right ?
Cheers,
Ben.
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