Re: [PATCH] hardening: Refresh KCFI options, add some more

[Kees Cook]

On Tue, Apr 30, 2024 at 10:48:36AM -0700, Kees Cook wrote:
> On Tue, Apr 30, 2024 at 11:21:40AM +0200, Peter Zijlstra wrote:
> > On Fri, Apr 26, 2024 at 03:29:44PM -0700, Kees Cook wrote:
> > 
> > > - CONFIG_CFI_CLANG=y for x86 and arm64. (And disable FINEIBT since
> > >   it isn't as secure as straight KCFI.)
> > 
> > Oi ?
> 
> Same objection I always had[1]: moving the check into the destination
> means attacks with control over executable memory contents can just omit
> the check.
> 
> But now that I went to go look I see 0c3e806ec0f9 ("x86/cfi: Add boot
> time hash randomization") is only enabled under FINEIBT... seems better
> if that were always enabled...

And FINEIBT actually can't be disabled... :|

And as it turns out CFI_CLANG doesn't work at all on v6.9...

[    0.587220] no CFI hash found at: __call_sites+0x339a8/0x34450 ffffffffac20cef8 00 00 00 00 00
[    0.588226] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:1182 __apply_fineibt+0x7a9/0x820
..
[    0.619220] SMP alternatives: Something went horribly wrong trying to rewrite the CFI implementation.
*hang*



-- 
Kees Cook