linux-kernel - [RFC v2 01/13] mm/kfence: Add a new kunit test test_use_after_free_read

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Message-ID: <a8ca8bd5eb4114304b34dd8bac7a6280d358c728.1726571179.git.ritesh.list@gmail.com>
Date: Thu, 19 Sep 2024 08:25:59 +0530
From: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To: linuxppc-dev@...ts.ozlabs.org
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Donet Tom <donettom@...ux.vnet.ibm.com>,
	Pavithra Prakash <pavrampu@...ux.vnet.ibm.com>,
	Nirjhar Roy <nirjhar@...ux.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kasan-dev@...glegroups.com,
	"Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	linux-mm@...ck.org
Subject: [RFC v2 01/13] mm/kfence: Add a new kunit test test_use_after_free_read_nofault()

From: Nirjhar Roy <nirjhar@...ux.ibm.com>

Faults from copy_from_kernel_nofault() needs to be handled by fixup
table and should not be handled by kfence. Otherwise while reading
/proc/kcore which uses copy_from_kernel_nofault(), kfence can generate
false negatives. This can happen when /proc/kcore ends up reading an
unmapped address from kfence pool.

Let's add a testcase to cover this case.

Co-developed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Signed-off-by: Nirjhar Roy <nirjhar@...ux.ibm.com>
Cc: kasan-dev@...glegroups.com
Cc: Alexander Potapenko <glider@...gle.com>
Cc: linux-mm@...ck.org
---
 mm/kfence/kfence_test.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index 00fd17285285..f65fb182466d 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -383,6 +383,22 @@ static void test_use_after_free_read(struct kunit *test)
 	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
 }

+static void test_use_after_free_read_nofault(struct kunit *test)
+{
+	const size_t size = 32;
+	char *addr;
+	char dst;
+	int ret;
+
+	setup_test_cache(test, size, 0, NULL);
+	addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+	test_free(addr);
+	/* Use after free with *_nofault() */
+	ret = copy_from_kernel_nofault(&dst, addr, 1);
+	KUNIT_EXPECT_EQ(test, ret, -EFAULT);
+	KUNIT_EXPECT_FALSE(test, report_available());
+}
+
 static void test_double_free(struct kunit *test)
 {
 	const size_t size = 32;
@@ -780,6 +796,7 @@ static struct kunit_case kfence_test_cases[] = {
 	KFENCE_KUNIT_CASE(test_out_of_bounds_read),
 	KFENCE_KUNIT_CASE(test_out_of_bounds_write),
 	KFENCE_KUNIT_CASE(test_use_after_free_read),
+	KFENCE_KUNIT_CASE(test_use_after_free_read_nofault),
 	KFENCE_KUNIT_CASE(test_double_free),
 	KFENCE_KUNIT_CASE(test_invalid_addr_free),
 	KFENCE_KUNIT_CASE(test_corruption),
--
2.46.0