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Date: Tue, 26 Apr 2022 18:42:42 +0200
From: Alexander Potapenko <glider@...gle.com>
To: glider@...gle.com
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrey Konovalov <andreyknvl@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Christoph Hellwig <hch@....de>,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Ilya Leoshkevich <iii@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Kees Cook <keescook@...omium.org>,
Marco Elver <elver@...gle.com>,
Mark Rutland <mark.rutland@....com>,
Matthew Wilcox <willy@...radead.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
Pekka Enberg <penberg@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vegard Nossum <vegard.nossum@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
linux-mm@...ck.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v3 13/46] kmsan: implement kmsan_init(), initialize READ_ONCE_NOCHECK()
kmsan_init() is a macro that takes a possibly uninitialized value and
returns an initialized value of the same type. It can be used e.g. in
cases when a value comes from non-instrumented code to avoid false
positive reports.
In particular, we use kmsan_init() in READ_ONCE_NOCHECK() so that it
returns initialized values. This helps defeat false positives e.g. from
leftover stack contents accessed by stack unwinders.
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
Link: https://linux-review.googlesource.com/id/Icd1260073666f944922f031bfb6762379ba1fa38
---
include/asm-generic/rwonce.h | 5 +++--
include/linux/kmsan-checks.h | 40 ++++++++++++++++++++++++++++++++++++
mm/kmsan/Makefile | 5 ++++-
mm/kmsan/annotations.c | 28 +++++++++++++++++++++++++
4 files changed, 75 insertions(+), 3 deletions(-)
create mode 100644 mm/kmsan/annotations.c
diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
index 8d0a6280e9824..7cf993af8e1ea 100644
--- a/include/asm-generic/rwonce.h
+++ b/include/asm-generic/rwonce.h
@@ -25,6 +25,7 @@
#include <linux/compiler_types.h>
#include <linux/kasan-checks.h>
#include <linux/kcsan-checks.h>
+#include <linux/kmsan-checks.h>
/*
* Yes, this permits 64-bit accesses on 32-bit architectures. These will
@@ -69,14 +70,14 @@ unsigned long __read_once_word_nocheck(const void *addr)
/*
* Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
- * word from memory atomically but without telling KASAN/KCSAN. This is
+ * word from memory atomically but without telling KASAN/KCSAN/KMSAN. This is
* usually used by unwinding code when walking the stack of a running process.
*/
#define READ_ONCE_NOCHECK(x) \
({ \
compiletime_assert(sizeof(x) == sizeof(unsigned long), \
"Unsupported access size for READ_ONCE_NOCHECK()."); \
- (typeof(x))__read_once_word_nocheck(&(x)); \
+ kmsan_init((typeof(x))__read_once_word_nocheck(&(x))); \
})
static __no_kasan_or_inline
diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
index a6522a0c28df9..ecd8336190fc0 100644
--- a/include/linux/kmsan-checks.h
+++ b/include/linux/kmsan-checks.h
@@ -14,6 +14,44 @@
#ifdef CONFIG_KMSAN
+/*
+ * Helper functions that mark the return value initialized.
+ * See mm/kmsan/annotations.c.
+ */
+u8 kmsan_init_1(u8 value);
+u16 kmsan_init_2(u16 value);
+u32 kmsan_init_4(u32 value);
+u64 kmsan_init_8(u64 value);
+
+static inline void *kmsan_init_ptr(void *ptr)
+{
+ return (void *)kmsan_init_8((u64)ptr);
+}
+
+static inline char kmsan_init_char(char value)
+{
+ return (u8)kmsan_init_1((u8)value);
+}
+
+#define __decl_kmsan_init_type(type, fn) unsigned type : fn, signed type : fn
+
+/**
+ * kmsan_init - Make the value initialized.
+ * @val: 1-, 2-, 4- or 8-byte integer that may be treated as uninitialized by
+ * KMSAN.
+ *
+ * Return: value of @val that KMSAN treats as initialized.
+ */
+#define kmsan_init(val) \
+ ( \
+ (typeof(val))(_Generic((val), \
+ __decl_kmsan_init_type(char, kmsan_init_1), \
+ __decl_kmsan_init_type(short, kmsan_init_2), \
+ __decl_kmsan_init_type(int, kmsan_init_4), \
+ __decl_kmsan_init_type(long, kmsan_init_8), \
+ char : kmsan_init_char, \
+ void * : kmsan_init_ptr)(val)))
+
/**
* kmsan_poison_memory() - Mark the memory range as uninitialized.
* @address: address to start with.
@@ -48,6 +86,8 @@ void kmsan_check_memory(const void *address, size_t size);
#else
+#define kmsan_init(value) (value)
+
static inline void kmsan_poison_memory(const void *address, size_t size,
gfp_t flags)
{
diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
index a80dde1de7048..73b705cbf75b9 100644
--- a/mm/kmsan/Makefile
+++ b/mm/kmsan/Makefile
@@ -1,9 +1,11 @@
-obj-y := core.o instrumentation.o hooks.o report.o shadow.o
+obj-y := core.o instrumentation.o hooks.o report.o shadow.o annotations.o
KMSAN_SANITIZE := n
KCOV_INSTRUMENT := n
UBSAN_SANITIZE := n
+KMSAN_SANITIZE_kmsan_annotations.o := y
+
# Disable instrumentation of KMSAN runtime with other tools.
CC_FLAGS_KMSAN_RUNTIME := -fno-stack-protector
CC_FLAGS_KMSAN_RUNTIME += $(call cc-option,-fno-conserve-stack)
@@ -11,6 +13,7 @@ CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)
+CFLAGS_annotations.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME)
diff --git a/mm/kmsan/annotations.c b/mm/kmsan/annotations.c
new file mode 100644
index 0000000000000..8ccde90bcd12b
--- /dev/null
+++ b/mm/kmsan/annotations.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KMSAN annotations.
+ *
+ * The kmsan_init_SIZE functions reside in a separate translation unit to
+ * prevent inlining them. Clang may inline functions marked with
+ * __no_sanitize_memory attribute into functions without it, which effectively
+ * results in ignoring the attribute.
+ *
+ * Copyright (C) 2017-2022 Google LLC
+ * Author: Alexander Potapenko <glider@...gle.com>
+ *
+ */
+
+#include <linux/export.h>
+#include <linux/kmsan-checks.h>
+
+#define DECLARE_KMSAN_INIT(size, t) \
+ __no_sanitize_memory t kmsan_init_##size(t value) \
+ { \
+ return value; \
+ } \
+ EXPORT_SYMBOL(kmsan_init_##size)
+
+DECLARE_KMSAN_INIT(1, u8);
+DECLARE_KMSAN_INIT(2, u16);
+DECLARE_KMSAN_INIT(4, u32);
+DECLARE_KMSAN_INIT(8, u64);
--
2.36.0.rc2.479.g8af0fa9b8e-goog
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