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() for the memory corruption instrumentation but before pagefault_disable(). Added KMSAN and modified KASAN kunit tests and tested on x86_64. This is the part of PATCH series attempting to properly address bugzilla issue. Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@xxxxxxxxxxxxxx/ Suggested-by: Marco Elver <elver@xxxxxxxxxx> Reported-by: syzbot+61123a5daeb9f7454599@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599 Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505 Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx> --- mm/kasan/kasan_test_c.c | 8 ++------ mm/kmsan/kmsan_test.c | 17 +++++++++++++++++ mm/maccess.c | 5 +++-- 3 files changed, 22 insertions(+), 8 deletions(-) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index 0a226ab032d..5cff90f831d 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1954,7 +1954,7 @@ static void rust_uaf(struct kunit *test) KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf()); } -static void copy_from_to_kernel_nofault_oob(struct kunit *test) +static void copy_to_kernel_nofault_oob(struct kunit *test) { char *ptr; char buf[128]; @@ -1973,10 +1973,6 @@ static void copy_from_to_kernel_nofault_oob(struct kunit *test) KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); } - 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, @@ -2057,7 +2053,7 @@ 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), + 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 13236d579eb..9733a22c46c 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 f752f0c0fa3..a91a39a56cf 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -31,8 +31,9 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size) if (!copy_from_kernel_nofault_allowed(src, size)) return -ERANGE; + /* Make sure uninitialized kernel memory isn't copied. */ + kmsan_check_memory(src, size); pagefault_disable(); - instrument_read(src, size); if (!(align & 7)) copy_from_kernel_nofault_loop(dst, src, size, u64, Efault); if (!(align & 3)) @@ -63,8 +64,8 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) align = (unsigned long)dst | (unsigned long)src; - pagefault_disable(); instrument_write(dst, size); + pagefault_disable(); if (!(align & 7)) copy_to_kernel_nofault_loop(dst, src, size, u64, Efault); if (!(align & 3)) -- 2.34.1
