Messages in this thread | | | Date | Tue, 24 Feb 2015 15:01:30 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns |
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On 02/24/2015 02:56 PM, Andy Lutomirski wrote: > On Tue, Feb 24, 2015 at 2:52 PM, H. Peter Anvin <hpa@zytor.com> wrote: >> On 02/24/2015 02:25 PM, Andy Lutomirski wrote: >>> On Tue, Feb 24, 2015 at 10:51 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote: >>>> In all three 32-bit entry points, %eax is zero-extended to %rax. >>>> It is safe to do 32-bit compare when checking that syscall# >>>> is not too large. >>> >>> Applied. Thanks! >>> >> >> NAK NAK NAK NAK NAK!!!! >> >> We have already had this turn into a security issue not just once but >> TWICE, because someone decided to "optimize" the path by taking out the >> zero extend. >> >> The use of a 64-bit compare here is an intentional "belts and >> suspenders" safety issue. > > Fair enough. OK if I just undo that part of this patch? >
Actually this part should have been broken up. The word "several" in the patch description is by itself a cause to NAK the patch.
-hpa
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