Messages in this thread | | | Date | Sun, 19 Jul 2015 06:12:35 +0200 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for __arch_hweight*() |
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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.
So even if we're not 100% correct wrt stack traces in this case, I think that's ok.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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