On Thu, Jul 05, 2018 at 09:58:15AM +0200, Ingo Molnar wrote: > > * Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > > So that's still incomplete in that doesn't analyze the 32-bit build yet, right? > > > > We could do INT3s on 64-bit and NOPs on 32-bit. > > > > Or, possibly even better, we could just keep NOPs everywhere and instead > > make objtool smart enough to detect function fallthroughs. That should > > be pretty easy, actually. It already does it for C files. > > > > Something like the below should work, though it's still got a few > > issues: > > > > a) objtool is currently disabled for crypto code because it doesn't > > yet understand crypto stack re-alignments (which really needs > > fixing anyway); and > > > > b) it complains about the blank xen hypercalls falling through. Those > > aren't actual functions anyway, so we should probably annotate > > those somehow so that objtool ignores them anyway. > > > > I'm a bit swamped at the moment but I can fix those once I get a little > > more bandwidth. I at least verified that this patch caught the crypto > > missing RETs. > > Great, I'd be perfectly fine with such an approach. > > Also, if we have that then we could re-apply Alexey's patch and switch to INT3 > (only on 64-bit kernels) without any trouble, because objtool should detect any > execution flow bugs before the INT3 could trigger, right? > > I.e. any INT3 fault would show a combination of *both* an objtool bug and a > probable code flow bug - which I suspect would warrant crashing the box ... Sounds good to me. I can take Alexey's patch and submit a 64-bit version of it, along with the relevant objtool changes (though it may still be a few weeks before I get the chance). -- Josh
