From: Nirjhar Roy <nirjhar@xxxxxxxxxxxxx> 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@xxxxxxxxx> Signed-off-by: Nirjhar Roy <nirjhar@xxxxxxxxxxxxx> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx> --- Will be nice if we can get some feedback on this. v2 -> v3: ========= 1. Separated out this kfence kunit test from the larger powerpc+kfence+v3 series. 2. Dropped RFC tag [v2]: https://lore.kernel.org/linuxppc-dev/cover.1728954719.git.ritesh.list@xxxxxxxxx [powerpc+kfence+v3]: https://lore.kernel.org/linuxppc-dev/cover.1729271995.git.ritesh.list@xxxxxxxxx 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
