On Thu, Sep 11, 2025 at 12:03:02PM -0700, Eric Biggers wrote:
On Thu, Sep 11, 2025 at 10:51:45AM -0700, Eric Biggers wrote:
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+0x198/0xa00Any 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:
The KMSAN test failures bisect to the following commit:
commit f90b474a35744b5d43009e4fab232e74a3024cae Author: Vlastimil Babka <vbabka@suse.cz> Date: Mon Mar 10 13:40:17 2025 +0100 mm: Fix the flipped condition in gfpflags_allow_spinning()I'm not sure why. Apparently something related to lib/stackdepot.c.
Reverting that commit on top of upstream fixes the KMSAN tests.
Rolling back all the BPF (?) related changes that were made to lib/stackdepot.c in v6.15 fixes this too. Looks like there was a regression where stack traces stopped being saved in some cases.
diff --git a/lib/stackdepot.c b/lib/stackdepot.c index de0b0025af2b9..99e374d35b61d 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -638,12 +638,11 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, struct list_head *bucket; struct stack_record *found = NULL; depot_stack_handle_t handle = 0; struct page *page = NULL; void *prealloc = NULL; - bool allow_spin = gfpflags_allow_spinning(alloc_flags); - bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin; + bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC; unsigned long flags; u32 hash;
if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK)) return 0; @@ -678,11 +677,11 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, DEPOT_POOL_ORDER); if (page) prealloc = page_address(page); }
- if (in_nmi() || !allow_spin) { + if (in_nmi()) { /* We can never allocate in NMI context. */ WARN_ON_ONCE(can_alloc); /* Best effort; bail if we fail to take the lock. */ if (!raw_spin_trylock_irqsave(&pool_lock, flags)) goto exit; @@ -719,14 +718,11 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, printk_deferred_exit(); raw_spin_unlock_irqrestore(&pool_lock, flags); exit: if (prealloc) { /* Stack depot didn't use this memory, free it. */ - if (!allow_spin) - free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER); - else - free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); + free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); } if (found) handle = found->handle.handle; return handle; }