Instrument copy_from_kernel_nofault() with KMSAN for uninitialized kernel memory check and copy_to_kernel_nofault() with KASAN, KCSAN to detect the memory corruption. syzbot reported that bpf_probe_read_kernel() kernel helper triggered KASAN report via kasan_check_range() which is not the expected behaviour as copy_from_kernel_nofault() is meant to be a non-faulting helper. Solution is, suggested by Marco Elver, to replace KASAN, KCSAN check in copy_from_kernel_nofault() with KMSAN detection of copying uninitilaized kernel memory. In copy_to_kernel_nofault() we can retain instrument_write() explicitly for the memory corruption instrumentation. copy_to_kernel_nofault() is tested on x86_64 and arm64 with CONFIG_KASAN_SW_TAGS. On arm64 with CONFIG_KASAN_HW_TAGS, kunit test currently fails. Need more clarification on it. Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@xxxxxxxxxxxxxx/ Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Suggested-by: Marco Elver <elver@xxxxxxxxxx> Reported-by: syzbot+61123a5daeb9f7454599@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599 Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505 Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx> --- v2: - squashed previous submitted in -mm tree 2 patches based on Linus tree v3: - moved checks to *_nofault_loop macros per Marco's comments - edited the commit message v4: - replaced Suggested-by with Reviewed-by v5: - addressed Andrey's comment on deleting CONFIG_KASAN_HW_TAGS check in mm/kasan/kasan_test_c.c - added explanatory comment in kasan_test_c.c - added Suggested-by: Marco Elver back per Andrew's comment. --- mm/kasan/kasan_test_c.c | 37 +++++++++++++++++++++++++++++++++++++ mm/kmsan/kmsan_test.c | 17 +++++++++++++++++ mm/maccess.c | 10 ++++++++-- 3 files changed, 62 insertions(+), 2 deletions(-) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index a181e4780d9d..cb6ad84641ec 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1954,6 +1954,42 @@ static void rust_uaf(struct kunit *test) KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf()); } +static void copy_to_kernel_nofault_oob(struct kunit *test) +{ + char *ptr; + char buf[128]; + size_t size = sizeof(buf); + + /* This test currently fails with the HW_TAGS mode. + * The reason is unknown and needs to be investigated. */ + ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(ptr); + + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) { + /* Check that the returned pointer is tagged. */ + KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_MIN); + KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); + } + + /* + * We test copy_to_kernel_nofault() to detect corrupted memory that is + * being written into the kernel. In contrast, copy_from_kernel_nofault() + * is primarily used in kernel helper functions where the source address + * might be random or uninitialized. Applying KASAN instrumentation to + * copy_from_kernel_nofault() could lead to false positives. + * By focusing KASAN checks only on copy_to_kernel_nofault(), + * we ensure that only valid memory is written to the kernel, + * minimizing the risk of kernel corruption while avoiding + * false positives in the reverse case. + */ + 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), @@ -2027,6 +2063,7 @@ 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_to_kernel_nofault_oob), KUNIT_CASE(rust_uaf), {} }; diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c index 13236d579eba..9733a22c46c1 100644 --- a/mm/kmsan/kmsan_test.c +++ b/mm/kmsan/kmsan_test.c @@ -640,6 +640,22 @@ static void test_unpoison_memory(struct kunit *test) KUNIT_EXPECT_TRUE(test, report_matches(&expect)); } +static void test_copy_from_kernel_nofault(struct kunit *test) +{ + long ret; + char buf[4], src[4]; + size_t size = sizeof(buf); + + EXPECTATION_UNINIT_VALUE_FN(expect, "copy_from_kernel_nofault"); + kunit_info( + test, + "testing copy_from_kernel_nofault with uninitialized memory\n"); + + ret = copy_from_kernel_nofault((char *)&buf[0], (char *)&src[0], size); + USE(ret); + KUNIT_EXPECT_TRUE(test, report_matches(&expect)); +} + static struct kunit_case kmsan_test_cases[] = { KUNIT_CASE(test_uninit_kmalloc), KUNIT_CASE(test_init_kmalloc), @@ -664,6 +680,7 @@ static struct kunit_case kmsan_test_cases[] = { KUNIT_CASE(test_long_origin_chain), KUNIT_CASE(test_stackdepot_roundtrip), KUNIT_CASE(test_unpoison_memory), + KUNIT_CASE(test_copy_from_kernel_nofault), {}, }; diff --git a/mm/maccess.c b/mm/maccess.c index 518a25667323..3ca55ec63a6a 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -13,9 +13,14 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src, return true; } +/* + * The below only uses kmsan_check_memory() to ensure uninitialized kernel + * memory isn't leaked. + */ #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \ while (len >= sizeof(type)) { \ - __get_kernel_nofault(dst, src, type, err_label); \ + __get_kernel_nofault(dst, src, type, err_label); \ + kmsan_check_memory(src, sizeof(type)); \ dst += sizeof(type); \ src += sizeof(type); \ len -= sizeof(type); \ @@ -49,7 +54,8 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault); #define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \ while (len >= sizeof(type)) { \ - __put_kernel_nofault(dst, src, type, err_label); \ + __put_kernel_nofault(dst, src, type, err_label); \ + instrument_write(dst, sizeof(type)); \ dst += sizeof(type); \ src += sizeof(type); \ len -= sizeof(type); \ -- 2.34.1
