linux-kernel - [PATCH v3] mm: x86: instrument __get/__put_kernel

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Message-Id: <20240919105750.901303-1-snovitoll@gmail.com>
Date: Thu, 19 Sep 2024 15:57:50 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: andreyknvl@...il.com
Cc: akpm@...ux-foundation.org,
	bp@...en8.de,
	brauner@...nel.org,
	dave.hansen@...ux.intel.com,
	dhowells@...hat.com,
	dvyukov@...gle.com,
	glider@...gle.com,
	hpa@...or.com,
	kasan-dev@...glegroups.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	mingo@...hat.com,
	ryabinin.a.a@...il.com,
	snovitoll@...il.com,
	tglx@...utronix.de,
	vincenzo.frascino@....com,
	x86@...nel.org
Subject: [PATCH v3] mm: x86: instrument __get/__put_kernel_nofault

On Wed, Sep 18, 2024 at 8:15 PM Andrey Konovalov <andreyknvl@...il.com> wrote:
> You still have the same problem here.
>
> What I meant is:
>
> char *ptr;
> char buf[128 - KASAN_GRANULE_SIZE];
> size_t size = sizeof(buf);
>
> ptr = kmalloc(size, GFP_KERNEL);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> KUNIT_EXPECT_KASAN_FAIL(...);
> ...
>
> kfree(ptr);

Thanks for catching this! I've turned kunit test into OOB instead of UAF.
---
v3: changed kunit test from UAF to OOB case and git commit message.
---
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_oob() kunit test triggers 4 KASAN OOB bug reports
as expected for each copy_from/to_kernel_nofault call.

Reported-by: Andrey Konovalov <andreyknvl@...il.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>
---
 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..87fb59071e8c 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..d13f1a514750 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_oob(struct kunit *test)
+{
+	char *ptr;
+	char buf[128];
+	size_t size = sizeof(buf);
+
+	ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, 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));
+	kfree(ptr);
+}
+
 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_oob),
 	{}
 };
 
-- 
2.34.1