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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, joao@overdrivepizza.com
Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching
Date: Tue, 2 Nov 2021 19:17:15 +0100	[thread overview]
Message-ID: <YYGAq3qLfb+35X/M@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YYGAAVG5aRDKRHso@hirez.programming.kicks-ass.net>

On Tue, Nov 02, 2021 at 07:14:25PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 02, 2021 at 06:44:56PM +0100, Ard Biesheuvel wrote:
> > On Tue, 2 Nov 2021 at 16:15, Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Tue, Nov 02, 2021 at 01:57:44PM +0100, Peter Zijlstra wrote:
> > >
> > > > So how insane is something like this, have each function:
> > > >
> > > > foo.cfi:
> > > >       endbr64
> > > >       xorl $0xdeadbeef, %r10d
> > > >       jz foo
> > > >       ud2
> > > >       nop     # make it 16 bytes
> > > > foo:
> > > >       # actual function text goes here
> > > >
> > > >
> > > > And for each hash have two thunks:
> > > >
> > > >
> > > >       # arg: r11
> > > >       # clobbers: r10, r11
> > > > __x86_indirect_cfi_deadbeef:
> > > >       movl -9(%r11), %r10             # immediate in foo.cfi
> > > >       xorl $0xdeadbeef, %r10          # our immediate
> > > >       jz 1f
> > > >       ud2
> > > > 1:    ALTERNATIVE_2   "jmp *%r11",
> > > >                       "jmp __x86_indirect_thunk_r11", X86_FEATURE_RETPOLINE
> > > >                       "lfence; jmp *%r11", X86_FEATURE_RETPOLINE_AMD
> > > >
> > 
> > So are these supposed to go into the jump tables? If so, there still
> > needs to be a check against the boundary of the table at the call
> > site, to ensure that we are not calling something that we shouldn't.
> > 
> > If they are not going into the jump tables, I don't see the point of
> > having them, as only happy flow/uncomprised code would bother to use
> > them.
> 
> I don't understand. If you can scribble your own code, you can
> circumvent pretty much any range check anyway. But if you can't scribble
> your own code, you get to use the branch here and that checks the
> callsite and callee signature.
> 
> The range check isn't fundamental to CFI, having a check is the
> important thing AFAIU.

That is, how is a jump-table/range-check better than a hash-value match
check?

  reply	other threads:[~2021-11-02 18:17 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
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 [this message]
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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