Messages in this thread | | | Date | Wed, 17 Aug 2022 09:45:45 +0200 | From | Peter Zijlstra <> | Subject | Re: Simplify load_unaligned_zeropad() (was Re: [GIT PULL] Ceph updates for 5.20-rc1) |
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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.
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