Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 21 Jul 2015 17:13:12 -0700 | Subject | Re: [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for __arch_hweight*() |
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On Jul 18, 2015 9:13 PM, "Borislav Petkov" <bp@alien8.de> wrote: > > On Sat, Jul 18, 2015 at 10:57:14AM -0500, Josh Poimboeuf wrote: > > Currently, when stackvalidate sees an ALTERNATIVE, it assumes that > > either code path is possible, so it follows both paths in parallel. > > > > If I understand right, you're proposing that stackvalidate should only > > follow the POPCNT path and never follow the !POPCNT path? > > Actually, you don't even need to follow the POPCNT case either because > it is a single instruction - no stack operations there. > > So yeah, either that or special-case the case where the original insn is > CALL and the replacement is a POPCNT and ignore those CALL locations. > > The advantage is that the burden is put on the tool and not by adding > markers to kernel code paths. > > > In general, I agree, and I like the original patch much better. IMO, it > > achieved the goal of keeping the kernel code clean, while fixing the > > frame pointer bug. > > And I think that in that case, adding that rSP dependency is too much > because even though it fixes the "bug", it is very very unlikely any > stack trace will have __sw_hweight* in it for reasons pointed out > earlier and also because those functions can't fail and they get > integral types as args which can't fail when deref-fing either. And even > if they do, they don't call any other functions so rIP pointing to them > is already enough.
Enough for oopses, perhaps, but maybe not enough for perf.
It sounds like you want CFI unwinding :)
--Andy
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