linux-hardening - Re: [RFC PATCH v2 06/21] cfi: Switch to -fsanitize=kcfi

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Date:   Sat, 14 May 2022 20:41:35 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev
Subject: Re: [RFC PATCH v2 06/21] cfi: Switch to -fsanitize=kcfi

On Fri, May 13, 2022 at 01:21:44PM -0700, Sami Tolvanen wrote:
> Switch from Clang's original forward-edge control-flow integrity
> implementation to -fsanitize=kcfi, which is better suited for the
> kernel, as it doesn't require LTO, doesn't use a jump table that
> requires altering function references, and won't break cross-module
> function address equality.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Looks good on arm64 with LKDTM, too:

[   96.904483] lkdtm: Performing direct entry CFI_FORWARD_PROTO
[   96.904718] lkdtm: Calling matched prototype ...
[   96.904829] lkdtm: Calling mismatched prototype ...
[   96.905250] CFI failure at lkdtm_CFI_FORWARD_PROTO+0x54/0x94 [lkdtm] (target: lkdtm_increment_int+0x0/0x20 [lkdtm]; expected type: 0x7e0c52a5)

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

-Kees

-- 
Kees Cook