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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757619074; bh=Qlsnxx5xoSOGiAxOfSS6gsBgNRLsgue6LjVool+d9vo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=exip/QW4v+IgClXJq68192Q8g2BA14FnRL3v6oxVrQVhnFn7FMEV52G1a8EYl9v49 PE654ArlxFQn+0nlJBVUp139EeUiOS/ZEI8Ba/H6wgpazoZsGJqgr1yhNa+RyRGztX +ZsA4LN2czoOdGXqNmvaHMbiTH8mvL2CzdMHVWqMy+RLbvijvCdOfP/wfWHVLPl84Z ZHaJj7k5Iiya8QZII8YDnIXGt+XsMQKWmnlEX+4NZb/37R22F6HmFCl74XoCnvi/Kt kj+LZtENT5LZrhO7SxwS7w8ji4b8y8BfwYm2gTmKN4rOLTM/7ZkeTykUO9QyCt16Er vTolONRdHF5xw== Date: Thu, 11 Sep 2025 12:29:53 -0700 From: Eric Biggers To: Alexander Potapenko Cc: Marco Elver , kasan-dev@googlegroups.com, Dmitry Vyukov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, stable@vger.kernel.org, Vlastimil Babka Subject: Re: [PATCH] kmsan: Fix out-of-bounds access to shadow memory Message-ID: <20250911192953.GG1376@sol> References: <20250829164500.324329-1-ebiggers@kernel.org> <20250910194921.GA3153735@google.com> <20250911175145.GA1376@sol> <20250911190302.GF1376@sol> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250911190302.GF1376@sol> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 38416A0006 X-Stat-Signature: peqesygam3pi9ruuxbs7eegt5nki3hbg X-Rspam-User: X-HE-Tag: 1757619076-282714 X-HE-Meta: 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 468qIBAC VPmPmDNJ2NNGhSPMtVw6FBWxX3EVkvKen2pNb7POak6B4u6+wrPV5646uPycmi7wGACDPH4K/km1TDqhGGw03JOFCCIknwOVutVBvNBwc17DIneIH2r3I01Et811SJMeP3PZfIsX485wvUB8BGZ7VsWnQVa7BU8Y1Xw9yRYEcZkhnl4MxaCbEzoNaNby48iC4AQTLqdxjYHKE7nCO3RS9R61HMjGI/vs8wFVRuNYNf47R8hgJ3F/zm0ppxZMLTx7rvk1oEFV4sEAiH0voJwt9M2OF3rqmx47MlYXfletI6e3LtnQVMUuPiri4YpNHPgWTaVpwCY6KUBSaPm83btS/oJv/NvOLg2g2MSWynZNL0Iv5lCc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 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: > > > > > > > > > > __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: > > The KMSAN test failures bisect to the following commit: > > commit f90b474a35744b5d43009e4fab232e74a3024cae > Author: Vlastimil Babka > 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; }