Re: [PATCH v3 00/39] x86: Kernel IBT

Peter Zijlstra
2022-03-04T21:39:59Z

On Fri, Mar 04, 2022 at 11:09:58AM -0800, Josh Poimboeuf wrote:
> On Thu, Mar 03, 2022 at 12:23:21PM +0100, Peter Zijlstra wrote:
> > Hi, another week, another series.
> >
> > Since last time:
> >
> > - fixed and tested kexec (redgecomb)
> > - s/4*HAS_KERNEL_IBT/ENDBR_INSN_SIZE/ (jpoimboe)
> > - re-arranged Xen patches to avoid churn (andyhpp)
> > - folded IBT_SEAL Kconfig and objtool options (jpoimboe)
> > - dropped direct call/jmp rewrite from objtool (jpoimboe)
> > - dropped UD1 poison (jpoimboe)
> > - fixed kprobe selftests (masami,naveen)
> > - fixed ftrace selftests (rostedt)
> > - simplified CET/INT3 selftests (jpoimboe)
> > - boot time msg on IBT (kees)
> > - objtool WARN_FUNC sym+off fallback (jpoimboe)
> > - picked up tags for unchanged patches
> > - probably more
> >
> > Supposedly clang-14-rc2 will work on this series, I'll validate the moment the
> > Debian package gets updated.
> >
> > Patches go on top of tip/master + arm64/for-next/linkage. Also available here:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git x86/wip.ibt
>
> I'm getting some warnings with CONFIG_X86_KERNEL_IBT=n:
>
> arch/x86/entry/entry_64.o: warning: objtool: irq_entries_start()+0x7: unreachable instruction
> arch/x86/kernel/ftrace_64.o: warning: objtool: return_to_handler()+0x2a: unreachable instruction

Blergh, those are INT3 instructions, the first is the LDT stub padding
while the second is that INT3 you asked about earlier.

I can mark then all using SLS style rules, but that then triggers:

arch/x86/kernel/reboot.o: warning: objtool: native_machine_emergency_restart()+0x8f: BUG: why am I validating an ignored function?

which does horrible things on purpose to tickle a tripple fault in order
to reboot the machine.

Perhaps we should ignore INT3 by default, just like NOP ?