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Subject[PATCH v4 05/10] build, kcsan: Add KCSAN build exceptions
From
This blacklists several compilation units from KCSAN. See the respective
inline comments for the reasoning.

Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
---
v3:
* Moved EFI stub build exception hunk from x86-specific patch, since
it's not x86-specific.
* Spelling "data-race" -> "data race".
---
drivers/firmware/efi/libstub/Makefile | 2 ++
kernel/Makefile | 5 +++++
kernel/sched/Makefile | 6 ++++++
mm/Makefile | 8 ++++++++
4 files changed, 21 insertions(+)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index ee0661ddb25b..5d0a645c0de8 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -31,7 +31,9 @@ KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
-D__DISABLE_EXPORTS

GCOV_PROFILE := n
+# Sanitizer runtimes are unavailable and cannot be linked here.
KASAN_SANITIZE := n
+KCSAN_SANITIZE := n
UBSAN_SANITIZE := n
OBJECT_FILES_NON_STANDARD := y

diff --git a/kernel/Makefile b/kernel/Makefile
index 74ab46e2ebd1..cc53f7c25446 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -23,6 +23,9 @@ endif
# Prevents flicker of uninteresting __do_softirq()/__local_bh_disable_ip()
# in coverage traces.
KCOV_INSTRUMENT_softirq.o := n
+# Avoid KCSAN instrumentation in softirq ("No shared variables, all the data
+# are CPU local" => assume no data races), to reduce overhead in interrupts.
+KCSAN_SANITIZE_softirq.o = n
# These are called from save_stack_trace() on slub debug path,
# and produce insane amounts of uninteresting coverage.
KCOV_INSTRUMENT_module.o := n
@@ -30,6 +33,7 @@ KCOV_INSTRUMENT_extable.o := n
# Don't self-instrument.
KCOV_INSTRUMENT_kcov.o := n
KASAN_SANITIZE_kcov.o := n
+KCSAN_SANITIZE_kcov.o := n
CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)

# cond_syscall is currently not LTO compatible
@@ -118,6 +122,7 @@ obj-$(CONFIG_RSEQ) += rseq.o

obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak.o
KASAN_SANITIZE_stackleak.o := n
+KCSAN_SANITIZE_stackleak.o := n
KCOV_INSTRUMENT_stackleak.o := n

$(obj)/configs.o: $(obj)/config_data.gz
diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile
index 21fb5a5662b5..e9307a9c54e7 100644
--- a/kernel/sched/Makefile
+++ b/kernel/sched/Makefile
@@ -7,6 +7,12 @@ endif
# that is not a function of syscall inputs. E.g. involuntary context switches.
KCOV_INSTRUMENT := n

+# There are numerous races here, however, most of them due to plain accesses.
+# This would make it even harder for syzbot to find reproducers, because these
+# bugs trigger without specific input. Disable by default, but should re-enable
+# eventually.
+KCSAN_SANITIZE := n
+
ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
# needed for x86 only. Why this used to be enabled for all architectures is beyond
diff --git a/mm/Makefile b/mm/Makefile
index d996846697ef..56c1964bb3a1 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -7,6 +7,14 @@ KASAN_SANITIZE_slab_common.o := n
KASAN_SANITIZE_slab.o := n
KASAN_SANITIZE_slub.o := n

+# These produce frequent data race reports: most of them are due to races on
+# the same word but accesses to different bits of that word. Re-enable KCSAN
+# for these when we have more consensus on what to do about them.
+KCSAN_SANITIZE_slab_common.o := n
+KCSAN_SANITIZE_slab.o := n
+KCSAN_SANITIZE_slub.o := n
+KCSAN_SANITIZE_page_alloc.o := n
+
# These files are disabled because they produce non-interesting and/or
# flaky coverage that is not a function of syscall inputs. E.g. slab is out of
# free pages, or a task is migrated between nodes.
--
2.24.0.rc1.363.gb1bccd3e3d-goog
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