[PATCH v4 07/45] kmsan: introduce __no_sanitize_memory and __no_kmsan_checks

[Alexander Potapenko <glider@google.com>]

__no_sanitize_memory is a function attribute that instructs KMSAN to
skip a function during instrumentation. This is needed to e.g. implement
the noinstr functions.

__no_kmsan_checks is a function attribute that makes KMSAN
ignore the uninitialized values coming from the function's
inputs, and initialize the function's outputs.

Functions marked with this attribute can't be inlined into functions
not marked with it, and vice versa. This behavior is overridden by
__always_inline.

__SANITIZE_MEMORY__ is a macro that's defined iff the file is
instrumented with KMSAN. This is not the same as CONFIG_KMSAN, which is
defined for every file.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
Link: https://linux-review.googlesource.com/id/I004ff0360c918d3cd8b18767ddd1381c6d3281be
---
 include/linux/compiler-clang.h | 23 +++++++++++++++++++++++
 include/linux/compiler-gcc.h   |  6 ++++++
 2 files changed, 29 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index c84fec767445d..4fa0cc4cbd2c8 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -51,6 +51,29 @@
 #define __no_sanitize_undefined
 #endif
 
+#if __has_feature(memory_sanitizer)
+#define __SANITIZE_MEMORY__
+/*
+ * Unlike other sanitizers, KMSAN still inserts code into functions marked with
+ * no_sanitize("kernel-memory"). Using disable_sanitizer_instrumentation
+ * provides the behavior consistent with other __no_sanitize_ attributes,
+ * guaranteeing that __no_sanitize_memory functions remain uninstrumented.
+ */
+#define __no_sanitize_memory __disable_sanitizer_instrumentation
+
+/*
+ * The __no_kmsan_checks attribute ensures that a function does not produce
+ * false positive reports by:
+ *  - initializing all local variables and memory stores in this function;
+ *  - skipping all shadow checks;
+ *  - passing initialized arguments to this function's callees.
+ */
+#define __no_kmsan_checks __attribute__((no_sanitize("kernel-memory")))
+#else
+#define __no_sanitize_memory
+#define __no_kmsan_checks
+#endif
+
 /*
  * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together
  * with no_sanitize("coverage"). Prior versions of Clang support coverage
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index a0c55eeaeaf16..63eb90eddad77 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -125,6 +125,12 @@
 #define __SANITIZE_ADDRESS__
 #endif
 
+/*
+ * GCC does not support KMSAN.
+ */
+#define __no_sanitize_memory
+#define __no_kmsan_checks
+
 /*
  * Turn individual warnings and errors on and off locally, depending
  * on version.
-- 
2.37.0.rc0.161.g10f37bed90-goog