On Tue, Oct 8, 2024 at 4:36 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > On Tue, 8 Oct 2024 at 12:14, Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx> wrote: > > > > 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 > > - currently, disabled in kunit test. > > I assume you retested. Did you also test the bpf_probe_read_kernel() > false positive no longer appears? I've tested on: - x86_64 with KMSAN - x86_64 with KASAN - arm64 with HW_TAGS -- still failing - arm64 with SW_TAGS Please see the testing result in the following link: https://gist.github.com/novitoll/e2ccb2162340f7f8a63b63ee3e0f9994 I've also tested bpf_probe_read_kernel() in x86_64 KMSAN build, it does trigger KMSAN, though I don't see explicitly copy_from_kernel* in stack frame. AFAIU, it's checked prior to it in text_poke_copy(). Attached the PoC in the comment of the link above: root@syzkaller:/tmp# uname -a Linux syzkaller 6.12.0-rc2-g441b500abd70 #10 SMP PREEMPT_DYNAMIC Wed Oct 9 00:17:59 +05 2024 x86_64 GNU/Linux root@syzkaller:/tmp# ./exploit [*] exploit start [+] program loaded! [ 139.778255] ===================================================== [ 139.778846] BUG: KMSAN: uninit-value in bcmp+0x155/0x290 [ 139.779311] bcmp+0x155/0x290 [ 139.779591] __text_poke+0xe2d/0x1120 [ 139.779950] text_poke_copy+0x1e7/0x2b0 [ 139.780297] bpf_arch_text_copy+0x41/0xa0 [ 139.780665] bpf_dispatcher_change_prog+0x12dd/0x16b0 [ 139.781324] bpf_prog_test_run_xdp+0xbf0/0x1d20 [ 139.781898] bpf_prog_test_run+0x5d6/0x9a0 [ 139.782372] __sys_bpf+0x758/0xf10 [ 139.782759] __x64_sys_bpf+0xdd/0x130 [ 139.783178] x64_sys_call+0x1a21/0x4e10 [ 139.783610] do_syscall_64+0xcd/0x1b0 [ 139.784039] entry_SYSCALL_64_after_hwframe+0x67/0x6f [ 139.784597] [ 139.784779] Uninit was created at: [ 139.785197] __alloc_pages_noprof+0x717/0xe70 [ 139.785689] alloc_pages_bulk_noprof+0x17e1/0x20e0 [ 139.786223] alloc_pages_bulk_array_mempolicy_noprof+0x49e/0x5b0 [ 139.786873] __vmalloc_node_range_noprof+0xef2/0x24f0 [ 139.787414] execmem_alloc+0x1ec/0x4c0 [ 139.787841] bpf_jit_alloc_exec+0x3e/0x40 [ 139.788299] bpf_dispatcher_change_prog+0x430/0x16b0 [ 139.788837] bpf_prog_test_run_xdp+0xbf0/0x1d20 [ 139.789324] bpf_prog_test_run+0x5d6/0x9a0 [ 139.789774] __sys_bpf+0x758/0xf10 [ 139.790167] __x64_sys_bpf+0xdd/0x130 [ 139.790580] x64_sys_call+0x1a21/0x4e10 [ 139.791007] do_syscall_64+0xcd/0x1b0 [ 139.791423] entry_SYSCALL_64_after_hwframe+0x67/0x6f > > > Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@xxxxxxxxxxxxxx/ > > Suggested-by: Marco Elver <elver@xxxxxxxxxx> > > This looks more reasonable: > > Reviewed-by: Marco Elver <elver@xxxxxxxxxx> > > This looks like the most conservative thing to do for now. Done. > > > 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 > > --- > > mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++ > > mm/kmsan/kmsan_test.c | 17 +++++++++++++++++ > > mm/maccess.c | 10 ++++++++-- > > 3 files changed, 52 insertions(+), 2 deletions(-) > > > > diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c > > index a181e4780d9d..5cff90f831db 100644 > > --- a/mm/kasan/kasan_test_c.c > > +++ b/mm/kasan/kasan_test_c.c > > @@ -1954,6 +1954,32 @@ 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); > > + > > + /* Not detecting fails currently with HW_TAGS */ > > + KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS); > > + > > + 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); > > + } > > + > > + 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 +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_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 > >
