linux-kernel - [PATCH] cfi: Fix CFI failure with KASAN

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Message-ID: <20221222225747.3538676-1-samitolvanen@google.com>
Date:   Thu, 22 Dec 2022 22:57:47 +0000
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH] cfi: Fix CFI failure with KASAN

When CFI_CLANG and KASAN are both enabled, LLVM doesn't generate a
CFI type hash for asan.module_ctor functions in translation units
where CFI is disabled, which leads to a CFI failure during boot when
do_ctors calls the affected constructors:

  CFI failure at do_basic_setup+0x64/0x90 (target:
  asan.module_ctor+0x0/0x28; expected type: 0xa540670c)

Specifically, this happens because CFI is disabled for
kernel/cfi.c. There's no reason to keep CFI disabled here anymore, so
fix the failure by not filtering out CC_FLAGS_CFI for the file.

Note that https://reviews.llvm.org/rG3b14862f0a96 fixed the issue
where LLVM didn't emit CFI type hashes for any sanitizer constructors,
but now type hashes are emitted correctly for TUs that use CFI.

Link: https://github.com/ClangBuiltLinux/linux/issues/1742
Fixes: 89245600941e ("cfi: Switch to -fsanitize=kcfi")
Reported-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 kernel/Makefile | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/Makefile b/kernel/Makefile
index e7fc37a68069..10ef068f598d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -41,9 +41,6 @@ UBSAN_SANITIZE_kcov.o := n
 KMSAN_SANITIZE_kcov.o := n
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
 
-# Don't instrument error handlers
-CFLAGS_REMOVE_cfi.o := $(CC_FLAGS_CFI)
-
 obj-y += sched/
 obj-y += locking/
 obj-y += power/

base-commit: 8395ae05cb5a2e31d36106e8c85efa11cda849be
-- 
2.39.0.314.g84b9a713c41-goog