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Date:   Wed,  9 Dec 2020 11:01:52 +0100
Message-Id: <20201209100152.2492072-1-dvyukov@google.com>
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Subject: [PATCH] kcov: don't instrument with UBSAN
From:   Dmitry Vyukov <dvyukov@google.com>
To:     akpm@linux-foundation.org
Cc:     andreyknvl@google.com, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Dmitry Vyukov <dvyukov@google.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Marco Elver <elver@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Both KCOV and UBSAN use compiler instrumentation. If UBSAN detects a bug
in KCOV, it may cause infinite recursion via printk and other common
functions. We already don't instrument KCOV with KASAN/KCSAN for this
reason, don't instrument it with UBSAN as well.

As a side effect this also resolves the following gcc warning:

conflicting types for built-in function '__sanitizer_cov_trace_switch';
expected 'void(long unsigned int,  void *)' [-Wbuiltin-declaration-mismatch]

It's only reported when kcov.c is compiled with any of the sanitizers
enabled. Size of the arguments is correct, it's just that gcc uses 'long'
on 64-bit arches and 'long long' on 32-bit arches, while kernel type is
always 'long long'.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
---
 kernel/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/Makefile b/kernel/Makefile
index aac15aeb9d69..efa42857532b 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -34,8 +34,11 @@ KCOV_INSTRUMENT_extable.o := n
 KCOV_INSTRUMENT_stacktrace.o := n
 # Don't self-instrument.
 KCOV_INSTRUMENT_kcov.o := n
+# If sanitizers detect any issues in kcov, it may lead to recursion
+# via printk, etc.
 KASAN_SANITIZE_kcov.o := n
 KCSAN_SANITIZE_kcov.o := n
+UBSAN_SANITIZE_kcov.o := n
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack) -fno-stack-protector
 
 obj-y += sched/
-- 
2.29.2.576.ga3fc446d84-goog