Messages in this thread | | | Date | Thu, 24 Feb 2022 10:10:12 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 24/29] x86/text-patching: Make text_gen_insn() IBT aware |
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On Wed, Feb 23, 2022 at 05:18:04PM -0800, Joao Moreira wrote: > > +#ifdef CONFIG_X86_IBT > > + if (is_endbr(dest)) > > + dest += 4; > > +#endif > > Hi, FWIIW I saw this snippet trigger a bug in the jump_label infra where the > target displacement would not fit in a JMP8 operand.
Bah, I was afraid of seening that :/
> For these cases perhaps we can verify if the displacement fits the operand > and, if not, simply ignore and lose the decode cycle which may not be a huge > problem and remains semantically correct. Seems more sensible than padding > jump tables with nops. In the meantime I'll investigate clang's behavior and > if it is really a bug, I'll work on a patch.
Urgh, trouble is, we're going to be re-writing a bunch of ENDBR to be UD1 0x0(%eax),%eax, and you really don't want to try and execute those.
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