[v2,1/1] mm, kasan, kmsan: copy_from/to_kernel_nofault

Commit Message

Sabyrzhan Tasbolatov Oct. 5, 2024, 4:48 p.m. UTC

Instrument copy_from_kernel_nofault() with KMSAN for uninitialized kernel
memory check and copy_to_kernel_nofault() with KASAN, KCSAN to detect
the memory corruption.

syzbot reported that bpf_probe_read_kernel() kernel helper triggered
KASAN report via kasan_check_range() which is not the expected behaviour
as copy_from_kernel_nofault() is meant to be a non-faulting helper.

Solution is, suggested by Marco Elver, to replace KASAN, KCSAN check in
copy_from_kernel_nofault() with KMSAN detection of copying uninitilaized
kernel memory. In copy_to_kernel_nofault() we can retain
instrument_write() for the memory corruption instrumentation but before
pagefault_disable().

copy_to_kernel_nofault() is tested on x86_64 and arm64 with
CONFIG_KASAN_SW_TAGS. On arm64 with CONFIG_KASAN_HW_TAGS,
kunit test currently fails. Need more clarification on it
- currently, disabled in kunit test.

Link: https://lore.kernel.org/linux-mm/[e-mail]/
Suggested-by: Marco Elver <[e-mail]>
Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
Reported-by: Andrey Konovalov <[e-mail]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Signed-off-by: Sabyrzhan Tasbolatov <[e-mail]>
---
v2:
	- squashed previous submitted in -mm tree 2 patches based on Linus tree
---
 mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++
 mm/kmsan/kmsan_test.c   | 17 +++++++++++++++++
 mm/maccess.c            |  7 +++++--
 3 files changed, 49 insertions(+), 2 deletions(-)

Patch

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index a181e4780d9d..5cff90f831db 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1954,6 +1954,32 @@  static void rust_uaf(struct kunit *test)
 	KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
 }
 
+static void copy_to_kernel_nofault_oob(struct kunit *test)
+{
+	char *ptr;
+	char buf[128];
+	size_t size = sizeof(buf);
+
+	/* Not detecting fails currently with HW_TAGS */
+	KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS);
+
+	ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);
+
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) {
+		/* Check that the returned pointer is tagged. */
+		KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_MIN);
+		KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
+	}
+
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		copy_to_kernel_nofault(&buf[0], ptr, size));
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		copy_to_kernel_nofault(ptr, &buf[0], size));
+	kfree(ptr);
+}
+
 static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(kmalloc_oob_right),
 	KUNIT_CASE(kmalloc_oob_left),
@@ -2027,6 +2053,7 @@  static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(match_all_not_assigned),
 	KUNIT_CASE(match_all_ptr_tag),
 	KUNIT_CASE(match_all_mem_tag),
+	KUNIT_CASE(copy_to_kernel_nofault_oob),
 	KUNIT_CASE(rust_uaf),
 	{}
 };
diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index 13236d579eba..9733a22c46c1 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -640,6 +640,22 @@  static void test_unpoison_memory(struct kunit *test)
 	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
 }
 
+static void test_copy_from_kernel_nofault(struct kunit *test)
+{
+	long ret;
+	char buf[4], src[4];
+	size_t size = sizeof(buf);
+
+	EXPECTATION_UNINIT_VALUE_FN(expect, "copy_from_kernel_nofault");
+	kunit_info(
+		test,
+		"testing copy_from_kernel_nofault with uninitialized memory\n");
+
+	ret = copy_from_kernel_nofault((char *)&buf[0], (char *)&src[0], size);
+	USE(ret);
+	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
 static struct kunit_case kmsan_test_cases[] = {
 	KUNIT_CASE(test_uninit_kmalloc),
 	KUNIT_CASE(test_init_kmalloc),
@@ -664,6 +680,7 @@  static struct kunit_case kmsan_test_cases[] = {
 	KUNIT_CASE(test_long_origin_chain),
 	KUNIT_CASE(test_stackdepot_roundtrip),
 	KUNIT_CASE(test_unpoison_memory),
+	KUNIT_CASE(test_copy_from_kernel_nofault),
 	{},
 };
 
diff --git a/mm/maccess.c b/mm/maccess.c
index 518a25667323..a91a39a56cfd 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -15,7 +15,7 @@  bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
 
 #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label)	\
 	while (len >= sizeof(type)) {					\
-		__get_kernel_nofault(dst, src, type, err_label);		\
+		__get_kernel_nofault(dst, src, type, err_label);	\
 		dst += sizeof(type);					\
 		src += sizeof(type);					\
 		len -= sizeof(type);					\
@@ -31,6 +31,8 @@  long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 	if (!copy_from_kernel_nofault_allowed(src, size))
 		return -ERANGE;
 
+	/* Make sure uninitialized kernel memory isn't copied. */
+	kmsan_check_memory(src, size);
 	pagefault_disable();
 	if (!(align & 7))
 		copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
@@ -49,7 +51,7 @@  EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
 
 #define copy_to_kernel_nofault_loop(dst, src, len, type, err_label)	\
 	while (len >= sizeof(type)) {					\
-		__put_kernel_nofault(dst, src, type, err_label);		\
+		__put_kernel_nofault(dst, src, type, err_label);	\
 		dst += sizeof(type);					\
 		src += sizeof(type);					\
 		len -= sizeof(type);					\
@@ -62,6 +64,7 @@  long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
 	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
 		align = (unsigned long)dst | (unsigned long)src;
 
+	instrument_write(dst, size);
 	pagefault_disable();
 	if (!(align & 7))
 		copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);