Messages in this thread | | | Date | Mon, 11 May 2015 14:42:27 -0700 | Subject | Re: VERIFY_READ/WRITE in uaccess.h? | From | Linus Torvalds <> |
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On Mon, May 11, 2015 at 2:05 PM, H. Peter Anvin <hpa@zytor.com> wrote: > On 05/10/2015 02:44 AM, Richard Weinberger wrote: >> Hi! >> >> While cleaning up UML's uaccess code I've noticed that not a single architecture >> is using VERIFY_READ/WRITE in access_ok(). >> One exception is UML, it uses the access type in one check which is in vain anyways. >> Also asm-generic/uaccess.h drops the type parameter silently. >> >> Why do we still carry it around? >> >> Is it because we want it for some future architecture which can benefit >> from it or just because nobody cared enough to do a tree-wide cleanup? >> I fear it is the latter... ;) >> > > Or, perhaps, nobody noticed?
Not a future architecture. A historical one.
I think the only architecture that needed the VERIFY_READ/WRITE distinction was the now-dropped i386, where it was used to decide if we needed to do the manual COW because the 80386 couldn't do COW correctly in kernel mode.
That one - for the same reasons - also checked the actual accesses, not just that the range was in user mode. Exactly because it needed to pre-COW the pages (even if that was then obviously racy in threaded environments - in practice it worked, and we tried to support the fundamentally broken i386 hardware protection model for a long time).
Linus
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