Messages in this thread | | | Date | Thu, 1 Jul 2004 11:27:28 -0400 | Subject | Re: A question about PROT_NONE on ARM and ARM26 | From | Scott Wood <> |
| |
On Wed, Jun 30, 2004 at 11:59:22PM +0100, Russell King wrote: > Ok, to fill in for just this bit, the domain covering user space mappings > always remains in "client" mode, so page protections are always checked. > PAGE_NONE does not have the "user" bit set, so both user space accesses > and ldrt/strt instructions will be unable to access the pages, which is > the desired behaviour. > > However, plain ldr and str instructions will access the page, but > get_user/put_user doesn't use them, and copy_from_user/copy_to_user > are carefully crafted to ensure that we hit the necessary permission > checks for each page it touches on the first access.
What if CONFIG_PREEMPT is enabled, and you get preempted after that first access, and another thread unmaps the page before you're finished with it?
-Scott - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |