linux-kernel - Re: [PATCH v5 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN

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Date:   Wed, 13 Oct 2021 12:02:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v5 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB

On Wed, Oct 13, 2021 at 11:16:47AM -0700, Sami Tolvanen wrote:
> This change introduces the DEFINE_CFI_IMMEDIATE_RETURN_STUB macro,
> which defines a stub function that immediately returns and when
> defined in the core kernel, always passes indirect call checking
> with CONFIG_CFI_CLANG. Note that this macro should only be used when
> a stub cannot be called using the correct function type.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

I remain a bit worried about this exception infrastructure, but it's the
best way forward right now.

One thought: add DEFINE_CFI_IMMEDIATE_RETURN_STUB (and maybe other
things to watch closely) to MAINTAINERS:

diff --git a/MAINTAINERS b/MAINTAINERS
index abdcbcfef73d..2c9a24fd6a3c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4553,6 +4553,7 @@ B:	https://github.com/ClangBuiltLinux/linux/issues
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/clang/features
 F:	include/linux/cfi.h
 F:	kernel/cfi.c
+K:	\bDEFINE_CFI_IMMEDIATE_RETURN_STUB\b
 
 CLEANCACHE API
 M:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook