Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 14 Dec 2017 13:44:03 -0800 | Subject | Re: [PATCH v2 11/17] selftests/x86/ldt_gdt: Prepare for access bit forced |
| |
On Thu, Dec 14, 2017 at 1:22 PM, Andy Lutomirski <luto@kernel.org> wrote: > > Which kind of kills the whole thing. There's no way the idea of > putting the LDT in a VMA is okay if it's RW.
Sure there is.
I really don't understand why you guys think it has to be RO.
All it has to be is not _user_ accessible. And that's a requirement regardless, because no way in hell should users be able to read the damn thing.
So it clearly needs to have the PAGE_USER bit clear (to avoid users accessing it directly), and it needs to be marked somehow for get_user_pages() to refuse it too, and access_ok() needs to fail it so that we can't do get_user/put_user on it.
But the whole RO vs RW is not fundamentally critical.
Now, I do agree that RO is much much better in general, and it avoids the requirement to play games with "access_ok()" and friends (assuming we're just ok with users reading it), but I disagree with the whole "this is fundamental".
Linus
| |