linux-kernel - [PATCH 3/3] kcsan: Disable branch tracing in core runtime

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Message-Id: <20200618093118.247375-4-elver@google.com>
Date:   Thu, 18 Jun 2020 11:31:18 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, paulmck@...nel.org
Cc:     will@...nel.org, peterz@...radead.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...nel.org, dvyukov@...gle.com,
        cai@....pw, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] kcsan: Disable branch tracing in core runtime

Disable branch tracing in core KCSAN runtime if branches are being
traced (TRACE_BRANCH_PROFILING). This it to avoid its performance
impact, but also avoid recursion in case KCSAN is enabled for the branch
tracing runtime.

The latter had already been a problem for KASAN:
https://lore.kernel.org/lkml/CANpmjNOeXmD5E3O50Z3MjkiuCYaYOPyi+1rq=GZvEKwBvLR0Ug@mail.gmail.com/

Signed-off-by: Marco Elver <elver@...gle.com>
---
 kernel/kcsan/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index fea064afc4f7..65ca5539c470 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -8,7 +8,7 @@ CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
 CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
-	-fno-stack-protector
+	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 obj-y := core.o debugfs.o report.o
 obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o
-- 
2.27.0.290.gba653c62da-goog