mm, kasan, kmsan: instrument copy_from/to_kernel_nofault

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() explicitly for the memory corruption instrumentation.

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.

[akpm@linux-foundation.org: fix comment layout, per checkpatch
Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@mail.gmail.com/
Link: https://lkml.kernel.org/r/20241011035310.2982017-1-snovitoll@gmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Reported-by: syzbot+61123a5daeb9f7454599@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>	[KASAN]
Tested-by: Andrey Konovalov <andreyknvl@gmail.com>	[KASAN]
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index d8fb281e439d..fe132ce3c2b3 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1928,6 +1928,41 @@ 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);
+
+	/*
+	 * This test currently fails with the HW_TAGS mode. The reason is
+	 * unknown and needs to be investigated.
+	 */
+	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);
+
+	/*
+	 * We test copy_to_kernel_nofault() to detect corrupted memory that is
+	 * being written into the kernel. In contrast,
+	 * copy_from_kernel_nofault() is primarily used in kernel helper
+	 * functions where the source address might be random or uninitialized.
+	 * Applying KASAN instrumentation to copy_from_kernel_nofault() could
+	 * lead to false positives.  By focusing KASAN checks only on
+	 * copy_to_kernel_nofault(), we ensure that only valid memory is
+	 * written to the kernel, minimizing the risk of kernel corruption
+	 * while avoiding false positives in the reverse case.
+	 */
+	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),
@@ -2000,6 +2035,7 @@ 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),
 	{}
 };