Messages in this thread | | | Date | Thu, 23 Apr 2015 17:49:26 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/asm/entry/64: better check for canonical address |
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On Thu, Apr 23, 2015 at 08:41:15AM -0700, Andy Lutomirski wrote: > I was rather vague there. Let me try again: > > If anyone in the AMD camp really cared, we could add a new bug flag > X86_BUG_SYSRET_NEEDS_CANONICAL_RCX and set it on Intel chips only, so > we could use alternatives to patch out the check when running on > sensible AMD hardware. This would speed the slow path up by a couple > of cycles on AMD chips. > > Does that make more sense? We could call it > X86_BUG_SYSRET_NEEDS_CANONICAL_RIP if that makes more sense.
Actually "...NEEDS_CANONICAL_RCX" makes more sense as this is what we're going to patch out eventually, if it makes sense - the RIP canonicalness test is being done as part of SYSRET, just RCX is not being tested.
Tell you what - how about I perf stat this first by commenting out that couple of instructions on AMD to see whether it brings anything.
Got an idea for a workload other than a kernel build? :-)
Although a kernel build should do a lot of syscalls too...
Thanks.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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