[PATCH v2] kasan: Disable branch tracing for core runtime

[Marco Elver]

During early boot, while KASAN is not yet initialized, it is possible to
enter reporting code-path and end up in kasan_report(). While
uninitialized, the branch there prevents generating any reports,
however, under certain circumstances when branches are being traced
(TRACE_BRANCH_PROFILING), we may recurse deep enough to cause kernel
reboots without warning.

To prevent similar issues in future, we should disable branch tracing
for the core runtime.

Link: 20200517011732.GE24705@shao2-debian/">https://lore.kernel.org/lkml/20200517011732.GE24705@shao2-debian/
Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
v2:
* Remove duplicate DISABLE_BRANCH_PROFILING from tags.c as reported by
  Qian Cai.
---
 mm/kasan/Makefile  | 16 ++++++++--------
 mm/kasan/generic.c |  1 -
 mm/kasan/tags.c    |  1 -
 3 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index 434d503a6525..de3121848ddf 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -15,14 +15,14 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
 
 # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
 # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
-CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_generic_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_init.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_quarantine.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-CFLAGS_tags_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_generic_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_init.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_quarantine.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
+CFLAGS_tags_report.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -DDISABLE_BRANCH_PROFILING
 
 obj-$(CONFIG_KASAN) := common.o init.o report.o
 obj-$(CONFIG_KASAN_GENERIC) += generic.o generic_report.o quarantine.o
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 56ff8885fe2e..098a7dbaced6 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -15,7 +15,6 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-#define DISABLE_BRANCH_PROFILING
 
 #include <linux/export.h>
 #include <linux/interrupt.h>
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 25b7734e7013..8a959fdd30e3 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -12,7 +12,6 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-#define DISABLE_BRANCH_PROFILING
 
 #include <linux/export.h>
 #include <linux/interrupt.h>
-- 
2.27.0.rc0.183.gde8f92d652-goog