+ mm-kfence-add-a-new-kunit-test-test_use_after_free_read_nofault.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/kfence: add a new kunit test test_use_after_free_read_nofault()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-kfence-add-a-new-kunit-test-test_use_after_free_read_nofault.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kfence-add-a-new-kunit-test-test_use_after_free_read_nofault.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Nirjhar Roy <nirjhar@linux.ibm.com>
Subject: mm/kfence: add a new kunit test test_use_after_free_read_nofault()
Date: Fri, 18 Oct 2024 23:16:01 +0530

Faults from copy_from_kernel_nofault() need 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.

Link: https://lkml.kernel.org/r/210e561f7845697a32de44b643393890f180069f.1729272697.git.ritesh.list@gmail.com
Signed-off-by: Nirjhar Roy <nirjhar@linux.ibm.com>
Co-developed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Tested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kfence/kfence_test.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

--- a/mm/kfence/kfence_test.c~mm-kfence-add-a-new-kunit-test-test_use_after_free_read_nofault
+++ a/mm/kfence/kfence_test.c
@@ -383,6 +383,22 @@ static void test_use_after_free_read(str
 	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_cas
 	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),
_

Patches currently in -mm which might be from nirjhar@linux.ibm.com are

mm-kfence-add-a-new-kunit-test-test_use_after_free_read_nofault.patch