On Thu, Jan 25, 2018 at 09:05:37AM -0800, Andy Lutomirski wrote: > On Thu, Jan 25, 2018 at 9:00 AM, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > > On Thu, 2018-01-25 at 10:56 -0600, Josh Poimboeuf wrote: > >> On Thu, Jan 25, 2018 at 04:03:18PM +0000, David Woodhouse wrote: > >> > On Thu, 2018-01-25 at 16:51 +0100, Borislav Petkov wrote: > >> > > > >> > > > And the seg fault is objtool's way of telling you you need a > >> > > > ANNOTATE_NOSPEC_ALTERNATIVE above the alternative ;-) > >> > > > >> > > Except that it blew up when I did this which doesn't have ALTERNATIVE > >> > > (it's the diff I saved :-)) > >> > > >> > Yeah, ANNOTATE_NOSPEC_ALTERNATIVE just tells objtool "don't look at the > >> > alternative; you're not going to like it". > >> > > >> > If you start putting a __fill_rsb() function out of line somewhere and > >> > only *calling* it from alternatives, then objtool is going to shit > >> > itself when it sees that function, regardless. > >> > >> Right, if you *really* want it always inline, the short term solution is > >> to just patch it in with X86_FEATURE_ALWAYS. > > > > And the whole problem here is that patching it in with alternatives is > > painful on kernels < 4.1 because back then, we didn't cope with > > oldinstr and altinstr being different lengths. > > > > And they don't want to fix *that* because kABI... > > > > I just stopped caring. > > Screw kABI. There are *many* real world users who depend on kABI, so it's a fact of life with no better known solution for the given constraints. If you have a better idea then I suggest you build your own enterprise distro. > Distros that use retpolines need their driver vendors to recompile no > matter what. Distros that use IBRS and refuse to use retpolines > should get put on a list of "didn't actually adequately mitigate > spectre". Retpolines don't need to break kABI. We can just detect when they're missing and report it to the user. And I don't think there's anybody *refusing* to use retpolines, is there? But they're still not fully baked, especially for Skylake+. IBRS was just easier to implement out of the gate. And it mitigates Spectre just fine, but it's too slow to stick with long term. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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