Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 24 Feb 2015 14:56:13 -0800 | Subject | Re: [PATCH 1/4] x86: entry.S: tidy up several suboptimal insns |
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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?
--Andy
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