On Tue, Aug 16, 2022 at 10:57:45AM -0700, Linus Torvalds wrote: > > > + if (insn_decode(&insn, (void *) regs->ip, len, INSN_MODE_KERN)) > > > + return false; > > > > We have insn_decode_kernel() for exactly this (very) common case. > > I did that originally, and then I undid it in disgust, because that > interface is too simple. > > In particular, it just uses MAX_INSN_SIZE blindly. Which I didn't want > to do when I actually had the instruction size. > > Yes, yes, I also check the decode size after-the-fact, but I didn't > want the decoder to even look at the invalid bytes. > > This exception case is about the data being at the end of the page, I > wanted the fixup to be aware of code being at the end of a page too. I don't want to argue this point too much; but I will anyway :-) IMO if the decoder ends up out of bounds its a decoder bug either way around. That is, we *know* there is a full instruction at the given IP because we got into this exception path. ( it would be possible to add further constraints on trapnr ) Irrespective of the length constraint given to the decoder, it should not decode/access things past this instruction (without being careful about it). Anyway, I'm fine with the patch as you have it.
