From: Peter Zijlstra <peterz@infradead.org>
To: Peter Collingbourne <pcc@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>,
Kees Cook <keescook@chromium.org>,
Mark Rutland <mark.rutland@arm.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Joao Moreira <joao@overdrivepizza.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
linux-hardening@vger.kernel.org,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
llvm@lists.linux.dev
Subject: Re: [RFC PATCH 00/21] KCFI support
Date: Wed, 4 May 2022 09:34:18 +0200 [thread overview]
Message-ID: <YnIses89/uPLrazS@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMn1gO614sMzKzP6qTCcXB0QCeEu-G7CHn_h=6ikCLkFo_Z2Dg@mail.gmail.com>
On Tue, May 03, 2022 at 03:35:34PM -0700, Peter Collingbourne wrote:
> On Mon, May 2, 2022 at 1:02 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, May 02, 2022 at 08:22:57AM -0700, Sami Tolvanen wrote:
> >
> > > > Anyway, I think I hate that __builtin, I'd *much* rather see a variable
> > > > attribute or qualifier for this, such that one can mark a function
> > > > pointer as not doing CFI.
> > > >
> > > > I simply doesn't make sense to have a builtin that operates on an
> > > > expression. The whole thing is about indirect calls, IOW function
> > > > pointers.
> > >
> > > I also thought an attribute would be more convenient, but the compiler
> > > folks prefer a built-in:
> > >
> > > https://reviews.llvm.org/D122673
> >
> > That seems to mostly worry about C++ things (overload sets, template
> > specialization, name mangling) we kernel folks don't seem to much care
> > about.
> >
> > I'll stick with saying type system makes more sense to me though.
>
> I'd say it's not only the C++ issues but more the "action at a
> distance" that's implied by having this be part of the type system.
> With this being in the function type it's hard to tell whether any
> particular call will have CFI disabled, without needing to go and look
> at how the function pointer is defined.
Look at how we use volatile:
*(volatile int *)(&foo)
we don't use volatile on actual variable definitions (much), but instead
cast it in at the usage site. Same can be done with this if so desired.
> On the other hand, if we
> explicitly mark up the calls with CFI disabled, the code becomes
> easier to audit (think Rust "unsafe" blocks).
I don't know any Rust. To me Rust still looks like line noise.
> Does it seem any better to you to have this be marked up via the
> function expression, rather than the call? The idea is that this would
> always compile to a check-free function call, no matter what "func"
> is:
>
> __builtin_kcfi_call_unchecked(func)(args)
>
> We already have this, to some degree, with KCFI as implemented: CFI
> checks are disabled if the function expression refers to a declared
> function. The builtin would allow overriding the decision to also
> disable CFI checks for function expressions that use the builtin. It
> also wouldn't preclude a type based system later on (the builtin would
> become effectively a cast to the "unchecked" type).
That's still a bit naf; you've effectively made that builtin a type-cast.
next prev parent reply other threads:[~2022-05-04 7:36 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-29 20:36 [RFC PATCH 00/21] KCFI support Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 01/21] efi/libstub: Filter out CC_FLAGS_CFI Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 02/21] arm64/vdso: " Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 03/21] kallsyms: Ignore __kcfi_typeid_ Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 04/21] cfi: Remove CONFIG_CFI_CLANG_SHADOW Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 05/21] cfi: Drop __CFI_ADDRESSABLE Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 06/21] cfi: Switch to -fsanitize=kcfi Sami Tolvanen
2022-04-30 9:09 ` Peter Zijlstra
2022-04-29 20:36 ` [RFC PATCH 07/21] cfi: Add type helper macros Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 08/21] arm64/crypto: Add types to indirect called assembly functions Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 09/21] arm64: Add CFI error handling Sami Tolvanen
2022-05-05 15:44 ` Mark Rutland
2022-05-05 16:23 ` Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 10/21] treewide: Drop function_nocfi Sami Tolvanen
2022-05-05 16:30 ` Mark Rutland
2022-05-05 16:51 ` Sami Tolvanen
2022-05-05 18:03 ` Mark Rutland
2022-04-29 20:36 ` [RFC PATCH 11/21] treewide: Drop WARN_ON_FUNCTION_MISMATCH Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 12/21] treewide: Drop __cficanonical Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 13/21] cfi: Add the cfi_unchecked macro Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 14/21] treewide: static_call: Pass call arguments to the macro Sami Tolvanen
2022-04-29 23:21 ` Peter Zijlstra
2022-04-30 0:49 ` Sami Tolvanen
2022-05-02 7:46 ` Peter Zijlstra
2022-04-29 20:36 ` [RFC PATCH 15/21] static_call: Use cfi_unchecked Sami Tolvanen
2022-04-29 23:23 ` Peter Zijlstra
2022-04-29 20:36 ` [RFC PATCH 16/21] objtool: Add support for CONFIG_CFI_CLANG Sami Tolvanen
2022-04-29 23:30 ` Peter Zijlstra
2022-04-30 1:00 ` Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 17/21] x86/tools/relocs: Ignore __kcfi_typeid_ relocations Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 18/21] x86: Add types to indirect called assembly functions Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 19/21] x86/purgatory: Disable CFI Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 20/21] x86/vdso: " Sami Tolvanen
2022-04-29 20:36 ` [RFC PATCH 21/21] x86: Add support for CONFIG_CFI_CLANG Sami Tolvanen
2022-04-30 9:24 ` Peter Zijlstra
2022-05-02 15:20 ` Sami Tolvanen
2022-04-29 22:53 ` [RFC PATCH 00/21] KCFI support Kees Cook
2022-04-30 9:02 ` Peter Zijlstra
2022-05-02 15:22 ` Sami Tolvanen
2022-05-02 19:55 ` Peter Zijlstra
2022-05-03 22:35 ` Peter Collingbourne
2022-05-04 7:34 ` Peter Zijlstra [this message]
2022-04-30 16:07 ` Kenton Groombridge
2022-05-02 15:31 ` Sami Tolvanen
2022-05-04 16:17 ` Mark Rutland
2022-05-04 16:41 ` Sami Tolvanen
2022-05-04 20:17 ` Sami Tolvanen
2022-05-05 12:36 ` Mark Rutland
2022-05-05 16:00 ` Sami Tolvanen
2022-05-05 17:14 ` Mark Rutland
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