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From: Nick Desaulniers <ndesaulniers@google.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: X86 ML <x86@kernel.org>, Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nathan Chancellor <nathan@kernel.org>,
	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 v3 11/16] x86/purgatory: Disable CFI
Date: Tue, 14 Sep 2021 15:31:14 -0700	[thread overview]
Message-ID: <CAKwvOd=q1xhn9OEyowWyMeDW8CbWW4=nRmdE1tHggjCZKr7xrA@mail.gmail.com> (raw)
In-Reply-To: <CABCJKudRDcwfkSK205Pb__hzLWQPUFhbjUtFPbctdPAycSOKQw@mail.gmail.com>

On Tue, Sep 14, 2021 at 1:30 PM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> On Tue, Sep 14, 2021 at 1:02 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Tue, Sep 14, 2021 at 12:11 PM Sami Tolvanen <samitolvanen@google.com> wrote:
> > >
> > > Disable CONFIG_CFI_CLANG for the stand-alone purgatory.ro.
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> >
> > I kind of prefer the existing convention that has explicit guards on
> > specific configs (ie. CONFIG_FUNCTION_TRACER, CONFIG_STACKPROTECTOR,
> > CONFIG_STACKPROTECTOR_STRONG, CONFIG_RETPOLINE); it's more obvious
> > which configs may introduce which flags that are problematic. This
> > patch is ok as is, but it kind of makes this Makefile more
> > inconsistent.  I would prefer we had the explicit checks.
>
> The Makefile does already use DISABLE_STACKLEAK_PLUGIN in a similar
> way, but I don't have a strong preference here.

mmm...DISABLE_STACKLEAK_PLUGIN adds to PURGATORY_CFLAGS. This patch
adds to PURGATORY_CFLAGS_REMOVE.

> I can move this into
> an ifdef if it makes things cleaner.
>
> > Does CFI actually do any instrumentation in these object files? I
> > guess issues in purgatory cause silent/hard to debug kexec failures?
>
> The compiler shouldn't add any actual CFI instrumentation here right
> now, but I would prefer to avoid issues in future.

Ok, good to know.
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2021-09-14 22:31 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 19:10 [PATCH v3 00/16] x86: Add support for Clang CFI Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 01/16] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-09-14 19:29   ` Nick Desaulniers
2021-09-14 21:01     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 02/16] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 03/16] linkage: Add DECLARE_ASM_FUNC_SYMBOL Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 04/16] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-09-14 19:36   ` Nick Desaulniers
2021-09-14 20:32     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 05/16] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-09-14 19:39   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 06/16] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 07/16] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-09-14 19:30   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 08/16] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-09-14 19:32   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 09/16] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-09-14 19:33   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 10/16] x86/extable: Mark handlers __cficanonical Sami Tolvanen
2021-09-14 19:37   ` Kees Cook
2021-09-14 20:38     ` Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 11/16] x86/purgatory: Disable CFI Sami Tolvanen
2021-09-14 20:02   ` Nick Desaulniers
2021-09-14 20:30     ` Sami Tolvanen
2021-09-14 22:31       ` Nick Desaulniers [this message]
2021-09-15  6:24         ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 12/16] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 13/16] x86, module: " Sami Tolvanen
2021-09-14 19:10 ` [PATCH v3 14/16] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-09-14 19:44   ` Kees Cook
2021-09-14 19:46   ` Nick Desaulniers
2021-09-14 19:10 ` [PATCH v3 15/16] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-09-14 19:40   ` Kees Cook
2021-09-14 19:10 ` [PATCH v3 16/16] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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