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From: Peter Zijlstra <peterz@infradead.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Mark Rutland <mark.rutland@arm.com>, X86 ML <x86@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-hardening@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	llvm@lists.linux.dev
Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching
Date: Mon, 1 Nov 2021 10:01:55 +0100	[thread overview]
Message-ID: <20211101090155.GW174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMj1kXF3n-oQ1WP8=asb60K6UjSYOtz5RVhrcoCoNq3v7mZdQg@mail.gmail.com>

On Mon, Nov 01, 2021 at 12:36:18AM +0100, Ard Biesheuvel wrote:
> On Sun, 31 Oct 2021 at 21:45, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Sun, Oct 31, 2021 at 09:21:56PM +0100, Ard Biesheuvel wrote:
> >
> > > That means we can support static calls on arm64 now without breaking
> > > Clang CFI, and work on a solution for the redundant jumps on a more
> > > relaxed schedule.
> >
> > Yes, arm64 has a 'problem' with having already merged the clang-cfi
> > stuff :/
> >
> > I'm hoping the x86 solution can be an alternative CFI scheme, I'm
> > starting to really hate this one. And I'm not at all convinced the
> > proposed scheme is the best possible scheme given the constraints of
> > kernel code. AFAICT it's a compromise made in userspace.
> 
> Your scheme only works with IBT: the value of %r11 is under the
> adversary's control so it could just point it at 'foo+0x10' if it
> wants to call foo indirectly, and circumvent the check. So without IBT
> (or BTI), I think the check fundamentally belongs in the caller, not
> in the callee.

How is that not true for the jump table approach? Like I showed earlier,
it is *trivial* to reconstruct the actual function pointer from a
jump-table entry pointer.

In any case, I really want the discussion to start at square one, and
show/explain why any chosen CFI scheme is actually good for the kernel.
Just because clang happened to have implemented it, doesn't make it the
most suitable scheme for the kernel.

  reply	other threads:[~2021-11-01  9:06 UTC|newest]

Thread overview: 117+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-13 18:16 [PATCH v5 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 01/15] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-10-13 18:59   ` Kees Cook
2021-10-14  0:44   ` Josh Poimboeuf
2021-10-14 10:22   ` Peter Zijlstra
2021-10-14 19:20     ` Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 02/15] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-10-13 18:59   ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 03/15] linkage: Add DECLARE_NOT_CALLED_FROM_C Sami Tolvanen
2021-10-13 19:00   ` Kees Cook
2021-10-15  2:51   ` Andy Lutomirski
2021-10-15 15:35     ` Sami Tolvanen
2021-10-15 15:55     ` Thomas Gleixner
2021-10-15 16:22       ` Andy Lutomirski
2021-10-15 16:47         ` Sami Tolvanen
2021-10-15 17:34           ` Andy Lutomirski
2021-10-15 17:57       ` Thomas Gleixner
2021-10-15 18:42         ` Sami Tolvanen
2021-10-15 19:35           ` Andy Lutomirski
2021-10-15 20:37             ` Sami Tolvanen
2021-10-16 21:12               ` Josh Poimboeuf
2021-10-18 17:08                 ` Sami Tolvanen
2021-10-15 22:17           ` Thomas Gleixner
2021-10-16 21:16             ` Josh Poimboeuf
2021-10-13 18:16 ` [PATCH v5 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-10-13 19:02   ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 05/15] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-10-13 19:03   ` Kees Cook
2021-10-13 19:20   ` Steven Rostedt
2021-10-13 18:16 ` [PATCH v5 06/15] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-10-13 19:04   ` Kees Cook
2021-10-13 19:20   ` Steven Rostedt
2021-10-13 18:16 ` [PATCH v5 07/15] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 08/15] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 09/15] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-10-14 11:21   ` Borislav Petkov
2021-10-14 16:07     ` Kees Cook
2021-10-14 17:31       ` Borislav Petkov
2021-10-14 18:24         ` Sami Tolvanen
2021-10-14 19:00           ` Nick Desaulniers
2021-10-14 18:47         ` Kees Cook
2021-10-14 18:52           ` Steven Rostedt
2021-10-14 19:06             ` Josh Poimboeuf
2021-10-13 18:16 ` [PATCH v5 10/15] x86/purgatory: Disable CFI Sami Tolvanen
2021-10-13 19:05   ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 11/15] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 12/15] x86, module: " Sami Tolvanen
2021-10-13 18:55   ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 13/15] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 14/15] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 15/15] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen
2021-10-13 18:56   ` Kees Cook
2021-10-13 19:07 ` [PATCH v5 00/15] x86: Add support for Clang CFI Kees Cook
2021-10-19 10:06 ` Alexander Lobakin
2021-10-19 15:40   ` Sami Tolvanen
2021-10-21 10:27 ` Alexander Lobakin
2021-10-26 20:16 ` Peter Zijlstra
2021-10-27 10:02   ` David Laight
2021-10-27 10:17     ` Peter Zijlstra
2021-10-27 12:05   ` Mark Rutland
2021-10-27 12:22     ` Ard Biesheuvel
2021-10-27 12:48       ` Peter Zijlstra
2021-10-27 13:04         ` Peter Zijlstra
2021-10-27 13:30           ` Ard Biesheuvel
2021-10-27 14:03             ` Peter Zijlstra
2021-10-27 14:18               ` Ard Biesheuvel
2021-10-27 14:36                 ` Peter Zijlstra
2021-10-27 15:50                 ` Sami Tolvanen
2021-10-27 15:55                   ` Ard Biesheuvel
2021-10-29 20:03                   ` Peter Zijlstra
2021-10-30  7:47                     ` [PATCH] static_call,x86: Robustify trampoline patching Peter Zijlstra
2021-10-30  8:16                       ` Peter Zijlstra
2021-11-02 17:35                         ` Kees Cook
2021-11-02 18:15                           ` Peter Zijlstra
2021-11-15 13:09                         ` Rasmus Villemoes
2021-10-30 17:19                       ` Ard Biesheuvel
2021-10-30 18:02                         ` Peter Zijlstra
2021-10-30 18:55                           ` Ard Biesheuvel
2021-10-31 16:24                             ` Ard Biesheuvel
2021-10-31 16:39                               ` Peter Zijlstra
2021-10-31 16:44                                 ` Ard Biesheuvel
2021-10-31 20:09                                   ` Peter Zijlstra
2021-10-31 20:21                                     ` Ard Biesheuvel
2021-10-31 20:44                                       ` Peter Zijlstra
2021-10-31 23:36                                         ` Ard Biesheuvel
2021-11-01  9:01                                           ` Peter Zijlstra [this message]
2021-11-01  9:36                                             ` David Laight
2021-11-01 14:14                                             ` Ard Biesheuvel
2021-11-02 12:57                                               ` Peter Zijlstra
2021-11-02 15:15                                                 ` Peter Zijlstra
2021-11-02 17:44                                                   ` Ard Biesheuvel
2021-11-02 18:14                                                     ` Peter Zijlstra
2021-11-02 18:17                                                       ` Peter Zijlstra
2021-11-02 18:18                                                       ` Ard Biesheuvel
2021-11-02 21:48                                                         ` Peter Zijlstra
2021-11-02 18:10                                                 ` Kees Cook
2021-11-02 21:02                                                   ` Andy Lutomirski
2021-11-02 23:13                                                     ` Kees Cook
2021-11-03  0:20                                                       ` Andy Lutomirski
2021-11-03  8:35                                                         ` Peter Zijlstra
2021-11-03 10:01                                                           ` David Laight
2021-11-03 19:32                                                           ` Andy Lutomirski
2021-11-02 21:19                                                   ` Peter Zijlstra
2021-11-11 12:15                       ` [tip: locking/urgent] " tip-bot2 for Peter Zijlstra
2021-10-30 19:07                     ` [PATCH v5 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-10-27 17:11           ` Kees Cook
2021-10-27 21:21             ` Peter Zijlstra
2021-10-27 22:27               ` Kees Cook
2021-10-28 11:09                 ` Peter Zijlstra
2021-10-28 17:12                   ` Kees Cook
2021-10-28 20:29                     ` Peter Zijlstra
2021-11-02 17:26                       ` Kees Cook
2021-11-01  4:13                 ` Andy Lutomirski
2021-10-27 12:46     ` Peter Zijlstra
2021-10-27 12:55     ` David Laight
2021-10-27 13:17       ` Mark Rutland
2021-10-27 21:31         ` David Laight

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