From nobody Wed Dec 17 12:38:26 2025 Received: from pdx-out-006.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-006.esa.us-west-2.outbound.mail-perimeter.amazon.com [52.26.1.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4311B3FB1B; Tue, 30 Sep 2025 13:00:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.26.1.71 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759237237; cv=none; b=vBPhQfpT0qgXrk4TNgggK72pkdPHHjz5JDcR21g0Se5IouYfhmLYdk+LVre0bcD/7CCgVXNNSm7OQyQxFCDkIuJwTVSFtShyouBE1iTLriBjeUV4GMEsEWkzBuiYjpsgAuol7HEB8+vMBOH5LAUQRKSY58dIfKI8ZtbF/9cP4TA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759237237; c=relaxed/simple; bh=UJsfwDqFx/fhlLVWTizVS7mTfIl3qNGXsfhOUznPVeA=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=L4R2hkTK4hpRaPlwPOZSkvPqZqKiZwjAGu9YmNUYyxqVJCdCgGmQm97/nXY1SgH9Wo3IzL2KKs1seXxptjG+llS0ZLCO/zR7qDiZj8TgAtWqwYer6PS7HWHSMYKlmJXICb4fPgPmvTUgB9YigzcQyqSpXJbFjztkgOx0h6LTABk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de; spf=pass smtp.mailfrom=amazon.de; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b=KRIweQCD; arc=none smtp.client-ip=52.26.1.71 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b="KRIweQCD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.de; i=@amazon.de; q=dns/txt; s=amazoncorp2; t=1759237235; x=1790773235; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=4y9rVmjkhatWvM5IQXAd0quXaLLwCNEnONzYm/0o4vg=; b=KRIweQCD/Hz0TSpyoFjP8q/xMzBKzxxdNt8RxManMAU5gyCWSrbu2l/t Nh2mcWNt4hLoajYpEVNS/81gtsUq+6Q3xKmBJSzrCIBFWkwLXB8fTH0KC gRsehyK3Q72lKbB4Od8YlVhaQzVPVDlk3EpjmyPvCo7US37QcDKtiNR8n fXa7uisjoXMsl9Pho32Qa7a+1TYhFSZB0f0qaX8AsWH7XVHVtu9yvPIFK iVnmR0SFKd8FqiIrjvAE4BKUDYzFA9FIb8IgEmHeeW+TukBsn6WHz4def 16ev/246Zar4THwTNd6y7v8LyKjq5e+1NxluB/lcRG+TijbJxpubN9R6h g==; X-CSE-ConnectionGUID: U2bmbB3zQ6esQ+cFN2bi4Q== X-CSE-MsgGUID: T2b8wKMdQxSUE3HXqyo/mQ== X-IronPort-AV: E=Sophos;i="6.18,281,1751241600"; d="scan'208";a="4002597" Received: from ip-10-5-12-219.us-west-2.compute.internal (HELO smtpout.naws.us-west-2.prod.farcaster.email.amazon.dev) ([10.5.12.219]) by internal-pdx-out-006.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2025 13:00:32 +0000 Received: from EX19MTAUWC001.ant.amazon.com [10.0.7.35:22805] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.31.86:2525] with esmtp (Farcaster) id 143b7053-1d57-488d-839b-227c6cd39263; Tue, 30 Sep 2025 13:00:32 +0000 (UTC) X-Farcaster-Flow-ID: 143b7053-1d57-488d-839b-227c6cd39263 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWC001.ant.amazon.com (10.250.64.174) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Tue, 30 Sep 2025 13:00:32 +0000 Received: from dev-dsk-acsjakub-1b-6f9934e2.eu-west-1.amazon.com (172.19.75.107) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Tue, 30 Sep 2025 13:00:30 +0000 From: Jakub Acs To: CC: , Andrew Morton , "David Hildenbrand" , Xu Xin , Chengming Zhou , Peter Xu , Axel Rasmussen , , Subject: [PATCH v2] mm/ksm: fix flag-dropping behavior in ksm_madvise Date: Tue, 30 Sep 2025 13:00:23 +0000 Message-ID: <20250930130023.60106-1-acsjakub@amazon.de> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D041UWB004.ant.amazon.com (10.13.139.143) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" syzkaller discovered the following crash: (kernel BUG) [ 44.607039] ------------[ cut here ]------------ [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NO= PTI [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-= rc6 #1 PREEMPT(none) [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460 [ 44.617726] Call Trace: [ 44.617926] [ 44.619284] userfaultfd_release+0xef/0x1b0 [ 44.620976] __fput+0x3f9/0xb60 [ 44.621240] fput_close_sync+0x110/0x210 [ 44.622222] __x64_sys_close+0x8f/0x120 [ 44.622530] do_syscall_64+0x5b/0x2f0 [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 44.623244] RIP: 0033:0x7f365bb3f227 Kernel panics because it detects UFFD inconsistency during userfaultfd_release_all(). Specifically, a VMA which has a valid pointer to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags. The inconsistency is caused in ksm_madvise(): when user calls madvise() with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode, it accidentally clears all flags stored in the upper 32 bits of vma->vm_flags. Assuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and int are 32-bit wide. This setup causes the following mishap during the &=3D ~VM_MERGEABLE assignment. VM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. After ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then promoted to unsigned long before the & operation. This promotion fills upper 32 bits with leading 0s, as we're doing unsigned conversion (and even for a signed conversion, this wouldn't help as the leading bit is 0). & operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff instead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears the upper 32-bits of its value. Fix it by changing `VM_MERGEABLE` constant to unsigned long. Modify all other VM_* flags constants for consistency. Note: other VM_* flags are not affected: This only happens to the VM_MERGEABLE flag, as the other VM_* flags are all constants of type int and after ~ operation, they end up with leading 1 and are thus converted to unsigned long with leading 1s. Note 2: After commit 31defc3b01d9 ("userfaultfd: remove (VM_)BUG_ON()s"), this is no longer a kernel BUG, but a WARNING at the same place: [ 45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067 but the root-cause (flag-drop) remains the same. Fixes: 7677f7fd8be76 ("userfaultfd: add minor fault registration mode") Signed-off-by: Jakub Acs Cc: Andrew Morton Cc: David Hildenbrand Cc: Xu Xin Cc: Chengming Zhou Cc: Peter Xu Cc: Axel Rasmussen Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org --- v1 -> v2:=20 - fix by adding ul to flag constants instead of explicit cast. - drop Mike Kravetz from cc, as the mail returned v1: https://lore.kernel.org/all/20250930063921.62354-1-acsjakub@amazon.de/ include/linux/mm.h | 72 +++++++++++++++++++++++----------------------- 1 file changed, 36 insertions(+), 36 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 1ae97a0b8ec7..26a5c0f78b36 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -246,57 +246,57 @@ extern unsigned int kobjsize(const void *objp); * vm_flags in vm_area_struct, see mm_types.h. * When changing, update also include/trace/events/mmflags.h */ -#define VM_NONE 0x00000000 +#define VM_NONE 0x00000000ul =20 -#define VM_READ 0x00000001 /* currently active flags */ -#define VM_WRITE 0x00000002 -#define VM_EXEC 0x00000004 -#define VM_SHARED 0x00000008 +#define VM_READ 0x00000001ul /* currently active flags */ +#define VM_WRITE 0x00000002ul +#define VM_EXEC 0x00000004ul +#define VM_SHARED 0x00000008ul =20 /* mprotect() hardcodes VM_MAYREAD >> 4 =3D=3D VM_READ, and so for r/w/x b= its. */ -#define VM_MAYREAD 0x00000010 /* limits for mprotect() etc */ -#define VM_MAYWRITE 0x00000020 -#define VM_MAYEXEC 0x00000040 -#define VM_MAYSHARE 0x00000080 +#define VM_MAYREAD 0x00000010ul /* limits for mprotect() etc */ +#define VM_MAYWRITE 0x00000020ul +#define VM_MAYEXEC 0x00000040ul +#define VM_MAYSHARE 0x00000080ul =20 -#define VM_GROWSDOWN 0x00000100 /* general info on the segment */ +#define VM_GROWSDOWN 0x00000100ul /* general info on the segment */ #ifdef CONFIG_MMU -#define VM_UFFD_MISSING 0x00000200 /* missing pages tracking */ +#define VM_UFFD_MISSING 0x00000200ul /* missing pages tracking */ #else /* CONFIG_MMU */ -#define VM_MAYOVERLAY 0x00000200 /* nommu: R/O MAP_PRIVATE mapping that mi= ght overlay a file mapping */ -#define VM_UFFD_MISSING 0 +#define VM_MAYOVERLAY 0x00000200ul /* nommu: R/O MAP_PRIVATE mapping that = might overlay a file mapping */ +#define VM_UFFD_MISSING 0ul #endif /* CONFIG_MMU */ -#define VM_PFNMAP 0x00000400 /* Page-ranges managed without "struct page",= just pure PFN */ -#define VM_UFFD_WP 0x00001000 /* wrprotect pages tracking */ +#define VM_PFNMAP 0x00000400ul /* Page-ranges managed without "struct page= ", just pure PFN */ +#define VM_UFFD_WP 0x00001000ul /* wrprotect pages tracking */ =20 -#define VM_LOCKED 0x00002000 -#define VM_IO 0x00004000 /* Memory mapped I/O or similar */ +#define VM_LOCKED 0x00002000ul +#define VM_IO 0x00004000ul /* Memory mapped I/O or similar */ =20 /* Used by sys_madvise() */ -#define VM_SEQ_READ 0x00008000 /* App will access data sequentially */ -#define VM_RAND_READ 0x00010000 /* App will not benefit from clustered rea= ds */ - -#define VM_DONTCOPY 0x00020000 /* Do not copy this vma on fork */ -#define VM_DONTEXPAND 0x00040000 /* Cannot expand with mremap() */ -#define VM_LOCKONFAULT 0x00080000 /* Lock the pages covered when they are = faulted in */ -#define VM_ACCOUNT 0x00100000 /* Is a VM accounted object */ -#define VM_NORESERVE 0x00200000 /* should the VM suppress accounting */ -#define VM_HUGETLB 0x00400000 /* Huge TLB Page VM */ -#define VM_SYNC 0x00800000 /* Synchronous page faults */ -#define VM_ARCH_1 0x01000000 /* Architecture-specific flag */ -#define VM_WIPEONFORK 0x02000000 /* Wipe VMA contents in child. */ -#define VM_DONTDUMP 0x04000000 /* Do not include in the core dump */ +#define VM_SEQ_READ 0x00008000ul /* App will access data sequentially */ +#define VM_RAND_READ 0x00010000ul /* App will not benefit from clustered r= eads */ + +#define VM_DONTCOPY 0x00020000ul /* Do not copy this vma on fork */ +#define VM_DONTEXPAND 0x00040000ul /* Cannot expand with mremap() */ +#define VM_LOCKONFAULT 0x00080000ul /* Lock the pages covered when they ar= e faulted in */ +#define VM_ACCOUNT 0x00100000ul /* Is a VM accounted object */ +#define VM_NORESERVE 0x00200000ul /* should the VM suppress accounting */ +#define VM_HUGETLB 0x00400000ul /* Huge TLB Page VM */ +#define VM_SYNC 0x00800000ul /* Synchronous page faults */ +#define VM_ARCH_1 0x01000000ul /* Architecture-specific flag */ +#define VM_WIPEONFORK 0x02000000ul /* Wipe VMA contents in child. */ +#define VM_DONTDUMP 0x04000000ul /* Do not include in the core dump */ =20 #ifdef CONFIG_MEM_SOFT_DIRTY -# define VM_SOFTDIRTY 0x08000000 /* Not soft dirty clean area */ +# define VM_SOFTDIRTY 0x08000000ul /* Not soft dirty clean area */ #else -# define VM_SOFTDIRTY 0 +# define VM_SOFTDIRTY 0ul #endif =20 -#define VM_MIXEDMAP 0x10000000 /* Can contain "struct page" and pure PFN p= ages */ -#define VM_HUGEPAGE 0x20000000 /* MADV_HUGEPAGE marked this vma */ -#define VM_NOHUGEPAGE 0x40000000 /* MADV_NOHUGEPAGE marked this vma */ -#define VM_MERGEABLE 0x80000000 /* KSM may merge identical pages */ +#define VM_MIXEDMAP 0x10000000ul /* Can contain "struct page" and pure PFN= pages */ +#define VM_HUGEPAGE 0x20000000ul /* MADV_HUGEPAGE marked this vma */ +#define VM_NOHUGEPAGE 0x40000000ul /* MADV_NOHUGEPAGE marked this vma */ +#define VM_MERGEABLE 0x80000000ul /* KSM may merge identical pages */ =20 #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS #define VM_HIGH_ARCH_BIT_0 32 /* bit only usable on 64-bit architectures */ --=20 2.47.3 Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christian Schlaeger Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597