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From: Thomas Gleixner <tglx@linutronix.de>
To: Kees Cook <keescook@chromium.org>, Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>,
	Sami Tolvanen <samitolvanen@google.com>, X86 ML <x86@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	linux-hardening@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH 05/15] x86: Implement function_nocfi
Date: Sat, 17 Apr 2021 01:02:49 +0200	[thread overview]
Message-ID: <87fszpu92e.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <202104161529.D9F98DA994@keescook>

On Fri, Apr 16 2021 at 15:37, Kees Cook wrote:

> On Fri, Apr 16, 2021 at 03:20:17PM -0700, Andy Lutomirski wrote:
>> But obviously there is code that needs real function pointers.  How
>> about making this a first-class feature, or at least hacking around it
>> more cleanly.  For example, what does this do:
>> 
>> char entry_whatever[];
>> wrmsrl(..., (unsigned long)entry_whatever);
>
> This is just casting. It'll still resolve to the jump table entry.
>
>> or, alternatively,
>> 
>> extern void func() __attribute__((nocfi));
>
> __nocfi says func() should not perform checking of correct jump table
> membership for indirect calls.
>
> But we don't want a global marking for a function to be ignored by CFI;
> we don't want functions to escape CFI -- we want specific _users_ to
> either not check CFI for indirect calls (__nocfi) or we want specific
> passed addresses to avoid going through the jump table
> (function_nocfi()).

And that's why you mark entire files to be exempt without any rationale
why it makes sense.

Thanks,

        tglx

  reply	other threads:[~2021-04-16 23:02 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 20:38 [PATCH 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 01/15] objtool: Find a destination for jumps beyond the section end Sami Tolvanen
2021-04-20 18:14   ` Josh Poimboeuf
2021-04-20 20:25     ` Sami Tolvanen
2021-04-20 22:55       ` Josh Poimboeuf
2021-04-20 22:58         ` Nick Desaulniers
2021-04-16 20:38 ` [PATCH 02/15] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-04-20 19:47   ` Josh Poimboeuf
2021-04-20 20:45     ` Sami Tolvanen
2021-04-16 20:38 ` [PATCH 03/15] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-04-16 20:38 ` [PATCH 04/15] static_call: Use global functions for the self-test Sami Tolvanen
2021-04-16 21:37   ` Thomas Gleixner
2021-04-17  0:16     ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 05/15] x86: Implement function_nocfi Sami Tolvanen
2021-04-16 21:18   ` Borislav Petkov
2021-04-16 21:49     ` Sami Tolvanen
2021-04-16 22:02       ` Borislav Petkov
2021-04-16 22:06         ` Andy Lutomirski
2021-04-16 22:14           ` Borislav Petkov
2021-04-16 22:20             ` Andy Lutomirski
2021-04-16 22:37               ` Kees Cook
2021-04-16 23:02                 ` Thomas Gleixner [this message]
2021-04-17 10:16                   ` Thomas Gleixner
2021-04-19 15:13                     ` Sami Tolvanen
2021-04-16 22:28           ` Kees Cook
2021-04-16 22:52             ` Andy Lutomirski
2021-04-16 22:58               ` Kees Cook
2021-04-16 23:40               ` Kees Cook
2021-04-17 23:19                 ` Andy Lutomirski
2021-04-17 23:53                   ` Thomas Gleixner
2021-04-18  0:11                     ` Andy Lutomirski
2021-04-18 16:17                       ` Thomas Gleixner
2021-04-18 22:57                         ` Andy Lutomirski
2021-04-19 15:20                           ` Sami Tolvanen
2021-04-19 15:26                       ` David Laight
2021-04-19 17:46                         ` Andy Lutomirski
2021-04-17 14:20             ` David Laight
2021-04-17 15:48               ` Andy Lutomirski
2021-04-19  8:40             ` Rasmus Villemoes
2021-04-19 16:45               ` Joao Moreira
2021-04-19 21:52               ` David Laight
2021-04-16 22:16         ` Kees Cook
2021-04-16 22:13       ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 06/15] x86: Avoid CFI jump tables in IDT and entry points Sami Tolvanen
2021-04-16 22:26   ` Thomas Gleixner
2021-04-16 23:56     ` Kees Cook
2021-04-17  0:02       ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 07/15] x86/ftrace: Use function_nocfi in MCOUNT_ADDR Sami Tolvanen
2021-04-16 20:38 ` [PATCH 08/15] x86/extable: Do not mark exception callback as CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 09/15] x86/alternatives: Use C int3 selftest but disable KASAN Sami Tolvanen
2021-04-17 11:37   ` Peter Zijlstra
2021-04-19 15:26     ` Sami Tolvanen
2021-04-20  7:19       ` Peter Zijlstra
2021-04-16 20:38 ` [PATCH 10/15] x86/purgatory: Disable CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 11/15] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-04-16 20:38 ` [PATCH 12/15] x86, module: " Sami Tolvanen
2021-04-16 20:38 ` [PATCH 13/15] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 14/15] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-04-16 20:38 ` [PATCH 15/15] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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