From: Peter Collingbourne <pcc@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Joao Moreira <joao@overdrivepizza.com>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
andrew.cooper3@citrix.com, keescook@chromium.org,
samitolvanen@google.com, mark.rutland@arm.com,
hjl.tools@gmail.com, alyssa.milburn@linux.intel.com,
ndesaulniers@google.com, gabriel.gomes@linux.intel.com,
rick.p.edgecombe@intel.com
Subject: Re: [RFC PATCH 01/11] x86: kernel FineIBT
Date: Wed, 4 May 2022 10:04:02 -0700 [thread overview]
Message-ID: <YnKx5a9WvJ1UhWPm@google.com> (raw)
In-Reply-To: <YnJTYzralOhGGmED@hirez.programming.kicks-ass.net>
On Wed, May 04, 2022 at 12:20:19PM +0200, Peter Zijlstra wrote:
> On Tue, May 03, 2022 at 03:02:44PM -0700, Josh Poimboeuf wrote:
>
> > I'm not really qualified to comment on this too directly since I haven't
> > looked very much at the variations on FineIBT/CFI/KCFI, and what the
> > protections and drawbacks are for each approach, and when it might even
> > make sense to combine them for a "paranoid user".
> >
> > Since we have multiple similar and possibly competing technologies being
> > discussed, one thing I do want to warn against is that we as kernel
> > developers tend to err on the side of giving people too many choices and
> > combinations which *never* get used.
>
> So I don't think there's going to be a user choice here. If there's
> hardware support, FineIBT makes more sense. That also means that kCFI no
> longer needs to worry about IBT.
>
> If we do something like:
>
>
> kCFI FineIBT
>
> __cfi_\sym: __cfi_\sym:
> endbr # 4 endbr # 4
> sub $hash, %r10 # 7 sub $hash, %r10 # 7
> je \sym # 2 je \sym # 2
> ud2 # 2 ud2 # 2
> \sym: \sym:
>
>
> caller: caller:
> cmpl $hash, -8(%r11) # 8 movl $hash, %r10d # 6
> je 1f # 2 sub 15, %r11 # 4
> ud2 # 2 call *%r11 # 3
> 1: call __x86_indirect_thunk_r11 # 5 .nop 4 # 4 (could even fix up r11 again)
>
>
> Then, all that's required is a slight tweak to apply_retpolines() to
> rewrite a little more text.
>
> Note that this also does away with having to fix up the linker, since
> all direct call will already point at \sym. It's just the IBT indirect
> calls that need to frob the pointer in order to hit the ENDBR.
>
> On top of that, we no longer have to special case the objtool
> instruction decoder, the prelude are proper instructions now.
For kCFI this brings back the gadget problem that I mentioned here:
https://lore.kernel.org/all/Yh7fLRYl8KgMcOe5@google.com/
because the hash at the call site is 8 bytes before the call
instruction.
Peter
next prev parent reply other threads:[~2022-05-04 17:32 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-20 0:42 [RFC PATCH 00/11] Kernel FineIBT Support joao
2022-04-20 0:42 ` [RFC PATCH 01/11] x86: kernel FineIBT joao
2022-04-29 1:37 ` Josh Poimboeuf
2022-05-02 17:17 ` Joao Moreira
2022-05-03 22:02 ` Josh Poimboeuf
2022-05-04 2:19 ` Joao Moreira
2022-05-04 10:20 ` Peter Zijlstra
2022-05-04 17:04 ` Peter Collingbourne [this message]
2022-05-04 18:16 ` Peter Zijlstra
2022-05-05 0:28 ` Sami Tolvanen
2022-05-05 7:36 ` Peter Zijlstra
2022-05-08 8:29 ` Kees Cook
2022-05-09 11:22 ` Peter Zijlstra
2022-04-20 0:42 ` [RFC PATCH 02/11] kbuild: Support FineIBT build joao
2022-04-20 0:42 ` [RFC PATCH 03/11] objtool: Support FineIBT offset fixes joao
2022-04-20 0:42 ` [RFC PATCH 04/11] x86/module: Support FineIBT in modules joao
2022-04-20 0:42 ` [RFC PATCH 05/11] x86/text-patching: Support FineIBT text-patching joao
2022-04-20 0:42 ` [RFC PATCH 06/11] x86/bpf: Support FineIBT joao
2022-04-20 0:42 ` [RFC PATCH 07/11] x86/lib: Prevent UACCESS call warning from objtool joao
2022-04-20 0:42 ` [RFC PATCH 08/11] x86/ibt: Add CET_TEST module for IBT testing joao
2022-04-20 0:42 ` [RFC PATCH 09/11] x86/FineIBT: Add FINEIBT_TEST module joao
2022-04-20 0:42 ` [RFC PATCH 10/11] linux/interrupt: Fix prototype matching property joao
2022-04-20 2:45 ` Kees Cook
2022-04-20 22:14 ` Joao Moreira
2022-04-20 0:42 ` [RFC PATCH 11/11] driver/int3400_thermal: Fix prototype matching joao
2022-04-20 2:55 ` Kees Cook
2022-04-20 22:28 ` Joao Moreira
2022-04-20 23:04 ` Kees Cook
2022-04-20 23:12 ` Joao Moreira
2022-04-20 23:25 ` Kees Cook
2022-04-21 0:28 ` Joao Moreira
2022-04-20 2:42 ` [RFC PATCH 00/11] Kernel FineIBT Support Kees Cook
2022-04-20 22:50 ` Joao Moreira
2022-04-20 7:40 ` Peter Zijlstra
2022-04-20 15:17 ` Josh Poimboeuf
2022-04-20 17:12 ` Nick Desaulniers
2022-04-20 22:40 ` Joao Moreira
2022-04-21 7:49 ` Peter Zijlstra
2022-04-21 15:23 ` Joao Moreira
2022-04-21 15:35 ` H.J. Lu
2022-04-21 22:11 ` Fangrui Song
2022-04-21 22:26 ` H.J. Lu
2022-04-20 23:34 ` Edgecombe, Rick P
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