Messages in this thread | | | Date | Wed, 30 Jun 2004 20:35:18 -0700 | From | William Lee Irwin III <> | Subject | Re: Testing PROT_NONE and other protections, and a surprise |
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William Lee Irwin III wrote: >> It would be a bug if copy_to_user()/copy_from_user() failed to return >> errors on attempted copies to/from areas with PROT_NONE protection. >> I recommend writing a testcase and submitting it to LTP. I'll follow up >> with an additional suggestion.
On Thu, Jul 01, 2004 at 04:26:06AM +0100, Jamie Lokier wrote: > I've just written a thorough test. The attached program tries every > combination of PROT_* flags, and tells you what protection you really get. > I don't know how tests get into LTP; perhaps I can leave that to you? > When running it on i386, I got a *huge* surprise (to me). A > PROT_WRITE-only page can sometimes fault on read or exec. This is the > output:
This is unsurprising. The permissions can't be represented in pagetables, but can opportunistically be enforced when exceptions are taken for other reasons (e.g. TLB invalidations related to page replacement).
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