[PATCH v2] mm: x86: instrument __get/__put_kernel_nofault

[Sabyrzhan Tasbolatov <snovitoll@gmail.com>]

Instrument copy_from_kernel_nofault(), copy_to_kernel_nofault(),
strncpy_from_kernel_nofault() where __put_kernel_nofault, __get_kernel_nofault
macros are used.

__get_kernel_nofault needs instrument_memcpy_before() which handles
KASAN, KCSAN checks for src, dst address, whereas for __put_kernel_nofault
macro, instrument_write() check should be enough as it's validated via
kmsan_copy_to_user() in instrument_put_user().

__get_user_size was appended with instrument_get_user() for KMSAN check in
commit 888f84a6da4d("x86: asm: instrument usercopy in get_user() and
put_user()") but only for CONFIG_CC_HAS_ASM_GOTO_OUTPUT.

copy_from_to_kernel_nofault() kunit test triggers 4 KASAN bug reports as
expected per each copy_from/to_kernel_nofault call.

Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
v2: added 2 tests for src, dst check and enhanced instrument check in macros

On Wed, Sep 18, 2024 at 3:51 AM Andrey Konovalov <andreyknvl@gmail.com> wrote:
>
> On Tue, Sep 17, 2024 at 10:18 PM Sabyrzhan Tasbolatov
> <snovitoll@gmail.com> wrote:
> >
> I think the easiest fix would be to allocate e.g. 128 -
> KASAN_GRANULE_SIZE bytes and do an out-of-bounds up to 128 bytes via
> copy_to/from_kernel_nofault. This will only corrupt the in-object
> kmalloc redzone, which is not harmful.

Hi Andrey,

Thanks for the comments. I've changed the target UAF buffer size to
KASAN_GRANULE_SIZE and added other test cases from bugzilla.
---
 arch/x86/include/asm/uaccess.h |  4 ++++
 mm/kasan/kasan_test.c          | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 3a7755c1a441..bd1ee79238a2 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -353,6 +353,7 @@ do {									\
 	default:							\
 		(x) = __get_user_bad();					\
 	}								\
+	instrument_get_user(x);						\
 } while (0)
 
 #define __get_user_asm(x, addr, err, itype)				\
@@ -620,6 +621,7 @@ do {									\
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
 #define __get_kernel_nofault(dst, src, type, err_label)			\
+	instrument_memcpy_before(dst, src, sizeof(type));		\
 	__get_user_size(*((type *)(dst)), (__force type __user *)(src),	\
 			sizeof(type), err_label)
 #else // !CONFIG_CC_HAS_ASM_GOTO_OUTPUT
@@ -627,6 +629,7 @@ do {									\
 do {									\
 	int __kr_err;							\
 									\
+	instrument_memcpy_before(dst, src, sizeof(type));		\
 	__get_user_size(*((type *)(dst)), (__force type __user *)(src),	\
 			sizeof(type), __kr_err);			\
 	if (unlikely(__kr_err))						\
@@ -635,6 +638,7 @@ do {									\
 #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT
 
 #define __put_kernel_nofault(dst, src, type, err_label)			\
+	instrument_write(dst, sizeof(type));		\
 	__put_user_size(*((type *)(src)), (__force type __user *)(dst),	\
 			sizeof(type), err_label)
 
diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
index 7b32be2a3cf0..9a3c4ad91d59 100644
--- a/mm/kasan/kasan_test.c
+++ b/mm/kasan/kasan_test.c
@@ -1899,6 +1899,26 @@ static void match_all_mem_tag(struct kunit *test)
 	kfree(ptr);
 }
 
+static void copy_from_to_kernel_nofault(struct kunit *test)
+{
+	char *ptr;
+	char buf[KASAN_GRANULE_SIZE];
+	size_t size = sizeof(buf);
+
+	ptr = kmalloc(size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	kfree(ptr);
+
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		copy_from_kernel_nofault(&buf[0], ptr, size));
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		copy_from_kernel_nofault(ptr, &buf[0], size));
+	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));
+}
+
 static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(kmalloc_oob_right),
 	KUNIT_CASE(kmalloc_oob_left),
@@ -1971,6 +1991,7 @@ 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_from_to_kernel_nofault),
 	{}
 };
 
-- 
2.34.1