On Thu, Sep 11, 2025 at 11:09:17AM +0200, Alexander Potapenko wrote:

On Wed, Sep 10, 2025 at 9:49 PM Eric Biggers ebiggers@kernel.org wrote:

...

On Fri, Aug 29, 2025 at 09:45:00AM -0700, Eric Biggers wrote:

...

Running sha224_kunit on a KMSAN-enabled kernel results in a crash in kmsan_internal_set_shadow_origin():

BUG: unable to handle page fault for address: ffffbc3840291000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 1810067 P4D 1810067 PUD 192d067 PMD 3c17067 PTE 0
Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 81 Comm: kunit_try_catch Tainted: G                 N  6.17.0-rc3 #10 PREEMPT(voluntary)
Tainted: [N]=TEST
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
RIP: 0010:kmsan_internal_set_shadow_origin+0x91/0x100
[...]
Call Trace:
<TASK>
__msan_memset+0xee/0x1a0
sha224_final+0x9e/0x350
test_hash_buffer_overruns+0x46f/0x5f0
? kmsan_get_shadow_origin_ptr+0x46/0xa0
? __pfx_test_hash_buffer_overruns+0x10/0x10
kunit_try_run_case+0x198/0xa00

Any thoughts on this patch from the KMSAN folks? I'd love to add CONFIG_KMSAN=y to my crypto subsystem testing, but unfortunately the kernel crashes due to this bug :-(

• Eric

Sorry, I was out in August and missed this email when digging through my inbox.

Curiously, I couldn't find any relevant crashes on the KMSAN syzbot instance, but the issue is legit. Thank you so much for fixing this!

Any chance you can add a test case for it to mm/kmsan/kmsan_test.c?

Unfortunately most of the KMSAN test cases already fail on upstream, which makes it difficult to develop new ones:

[ 1.322395] KTAP version 1 [ 1.322899] 1..1 [ 1.323644] KTAP version 1 [ 1.324142] # Subtest: kmsan [ 1.324650] # module: kmsan_test [ 1.324667] 1..24 [ 1.325990] # test_uninit_kmalloc: uninitialized kmalloc test (UMR report) [ 1.327078] *ptr is true [ 1.327525] # test_uninit_kmalloc: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:173 Expected report_matches(&expect) to be true, but is false [ 1.330117] not ok 1 test_uninit_kmalloc [ 1.330474] # test_init_kmalloc: initialized kmalloc test (no reports) [ 1.332129] *ptr is false [ 1.333384] ok 2 test_init_kmalloc [ 1.333729] # test_init_kzalloc: initialized kzalloc test (no reports) [ 1.335285] *ptr is false [ 1.339418] ok 3 test_init_kzalloc [ 1.339791] # test_uninit_stack_var: uninitialized stack variable (UMR report) [ 1.341484] cond is false [ 1.341927] # test_uninit_stack_var: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:211 Expected report_matches(&expect) to be true, but is false [ 1.344844] not ok 4 test_uninit_stack_var [ 1.345262] # test_init_stack_var: initialized stack variable (no reports) [ 1.347083] cond is true [ 1.347847] ok 5 test_init_stack_var [ 1.348145] # test_params: uninit passed through a function parameter (UMR report) [ 1.349926] arg1 is false [ 1.350338] arg2 is false [ 1.350746] arg is false [ 1.351154] arg1 is false [ 1.351561] arg2 is true [ 1.351987] # test_params: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:262 Expected report_matches(&expect) to be true, but is false [ 1.354751] not ok 6 test_params [ 1.355229] # test_uninit_multiple_params: uninitialized local passed to fn (UMR report) [ 1.357056] signed_sum3(a, b, c) is true [ 1.357677] # test_uninit_multiple_params: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:282 Expected report_matches(&expect) to be true, but is false [ 1.360393] not ok 7 test_uninit_multiple_params [ 1.360676] # test_uninit_kmsan_check_memory: kmsan_check_memory() called on uninit local (UMR report) [ 1.362916] # test_uninit_kmsan_check_memory: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:309 Expected report_matches(&expect) to be true, but is false [ 1.365946] not ok 8 test_uninit_kmsan_check_memory [ 1.366415] # test_init_kmsan_vmap_vunmap: pages initialized via vmap (no reports) [ 1.368805] ok 9 test_init_kmsan_vmap_vunmap [ 1.369223] # test_init_vmalloc: vmalloc buffer can be initialized (no reports) [ 1.371106] buf[0] is true [ 1.371937] ok 10 test_init_vmalloc [ 1.372396] # test_uaf: use-after-free in kmalloc-ed buffer (UMR report) [ 1.374021] value is true [ 1.374463] # test_uaf: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:378 Expected report_matches(&expect) to be true, but is false [ 1.376867] not ok 11 test_uaf [ 1.377229] # test_percpu_propagate: uninit local stored to per_cpu memory (UMR report) [ 1.378951] check is false [ 1.379432] # test_percpu_propagate: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:396 Expected report_matches(&expect) to be true, but is false [ 1.382201] not ok 12 test_percpu_propagate [ 1.382625] # test_printk: uninit local passed to pr_info() (UMR report) [ 1.384329] ffffc900002bfcd4 contains 0 [ 1.384933] # test_printk: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:418 Expected report_matches(&expect) to be true, but is false [ 1.387474] not ok 13 test_printk [ 1.387824] # test_init_memcpy: memcpy()ing aligned initialized src to aligned dst (no reports) [ 1.390061] ok 14 test_init_memcpy [ 1.390327] # test_memcpy_aligned_to_aligned: memcpy()ing aligned uninit src to aligned dst (UMR report) [ 1.392359] # test_memcpy_aligned_to_aligned: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:459 Expected report_matches(&expect) to be true, but is false [ 1.395181] not ok 15 test_memcpy_aligned_to_aligned [ 1.395467] # test_memcpy_aligned_to_unaligned: memcpy()ing aligned uninit src to unaligned dst (UMR report) [ 1.397845] # test_memcpy_aligned_to_unaligned: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:483 Expected report_matches(&expect) to be true, but is false [ 1.400221] # test_memcpy_aligned_to_unaligned: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:486 Expected report_matches(&expect) to be true, but is false [ 1.403059] not ok 16 test_memcpy_aligned_to_unaligned [ 1.403437] # test_memcpy_initialized_gap: unaligned 4-byte initialized value gets a nonzero origin after memcpy() - (2 UMR reports) [ 1.406077] # test_memcpy_initialized_gap: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:532 Expected report_matches(&expect) to be true, but is false [ 1.408340] # test_memcpy_initialized_gap: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:538 Expected report_matches(&expect) to be true, but is false [ 1.411063] not ok 17 test_memcpy_initialized_gap [ 1.411338] # test_memset16: memset16() should initialize memory [ 1.413393] ok 18 test_memset16 [ 1.413651] # test_memset32: memset32() should initialize memory [ 1.415427] ok 19 test_memset32 [ 1.415739] # test_memset64: memset64() should initialize memory [ 1.417513] ok 20 test_memset64 [ 1.417783] # test_long_origin_chain: origin chain exceeding KMSAN_MAX_ORIGIN_DEPTH (UMR report) [ 1.419805] # test_long_origin_chain: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:584 Expected report_matches(&expect) to be true, but is false [ 1.422415] not ok 21 test_long_origin_chain [ 1.422752] # test_stackdepot_roundtrip: testing stackdepot roundtrip (no reports) [ 1.424598] kunit_try_run_case+0x19d/0xa50 [ 1.425243] kunit_generic_run_threadfn_adapter+0x62/0xe0 [ 1.426252] kthread+0x8cd/0xb40 [ 1.426747] ret_from_fork+0x189/0x2b0 [ 1.427320] ret_from_fork_asm+0x1a/0x30 [ 1.428245] ok 22 test_stackdepot_roundtrip [ 1.428519] # test_unpoison_memory: unpoisoning via the instrumentation vs. kmsan_unpoison_memory() (2 UMR reports) [ 1.430771] ===================================================== [ 1.431682] BUG: KMSAN: uninit-value in test_unpoison_memory+0x146/0x3e0 [ 1.432705] test_unpoison_memory+0x146/0x3e0 [ 1.433356] kunit_try_run_case+0x19d/0xa50 [ 1.433979] kunit_generic_run_threadfn_adapter+0x62/0xe0 [ 1.434773] kthread+0x8cd/0xb40 [ 1.435263] ret_from_fork+0x189/0x2b0 [ 1.435846] ret_from_fork_asm+0x1a/0x30

[ 1.436692] Local variable a created at: [ 1.437270] test_unpoison_memory+0x41/0x3e0 [ 1.437903] kunit_try_run_case+0x19d/0xa50

[ 1.438766] Bytes 0-2 of 3 are uninitialized [ 1.439433] Memory access of size 3 starts at ffffc90000347cd5

[ 1.440517] CPU: 3 UID: 0 PID: 99 Comm: kunit_try_catch Tainted: G N 6.17.0-rc5-00110-ge59a039119c3 #3 PREEMPT(none) [ 1.442247] Tainted: [N]=TEST [ 1.442725] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 [ 1.444376] ===================================================== [ 1.445263] Disabling lock debugging due to kernel taint [ 1.446103] ===================================================== [ 1.447007] BUG: KMSAN: uninit-value in test_unpoison_memory+0x23f/0x3e0 [ 1.447996] test_unpoison_memory+0x23f/0x3e0 [ 1.448650] kunit_try_run_case+0x19d/0xa50 [ 1.449319] kunit_generic_run_threadfn_adapter+0x62/0xe0 [ 1.450122] kthread+0x8cd/0xb40 [ 1.450611] ret_from_fork+0x189/0x2b0 [ 1.451181] ret_from_fork_asm+0x1a/0x30

[ 1.452010] Local variable b created at: [ 1.452894] test_unpoison_memory+0x56/0x3e0 [ 1.453537] kunit_try_run_case+0x19d/0xa50

[ 1.454407] Bytes 0-2 of 3 are uninitialized [ 1.455043] Memory access of size 3 starts at ffffc90000347cd1

[ 1.456182] CPU: 3 UID: 0 PID: 99 Comm: kunit_try_catch Tainted: G B N 6.17.0-rc5-00110-ge59a039119c3 #3 PREEMPT(none) [ 1.457925] Tainted: [B]=BAD_PAGE, [N]=TEST [ 1.458545] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 [ 1.460239] ===================================================== [ 1.461617] ok 23 test_unpoison_memory [ 1.462056] # test_copy_from_kernel_nofault: testing copy_from_kernel_nofault with uninitialized memory [ 1.464122] ret is false [ 1.464538] # test_copy_from_kernel_nofault: EXPECTATION FAILED at mm/kmsan/kmsan_test.c:656 Expected report_matches(&expect) to be true, but is false [ 1.467250] not ok 24 test_copy_from_kernel_nofault [ 1.482563] # kmsan: pass:11 fail:13 skip:0 total:24 [ 1.483790] # Totals: pass:11 fail:13 skip:0 total:24 [ 1.484532] not ok 1 kmsan