On Jul 18, 2015 9:13 PM, "Borislav Petkov" <bp@xxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
