From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0F1A6170A11; Tue, 7 Oct 2025 21:01:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759870902; cv=none; b=SCKFfI4up5ukgjGcuHQ1hPOCuLLOzL8CYzAN8Gv3o5VZnC//t/7L7BrMLlTWtmTBkpeWzDaozOsD/P60HduYAEHlsG/cLzYSa9cixGptdE0JECbFedvDcFwkR8mxp2Y/wEL974XwaYE93rTQmnL06Ub+wwJNUplsanWDCzS/VL4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759870902; c=relaxed/simple; bh=Pa4n1uj1XQRZ/idsOah9mEXaKdyFWzFzQiSdelwinD8=; h=Date:To:From:Subject:Message-Id; b=S0EGtsyF41c78RXPBok9V1bU1Zjun11rq8dEyVxrSHqCIqReBZQD5rHAjJfeR5ADr+qwaN9Y/eG4OuhK/fqaKGyhFcNxRDZppH3gNZe4+7QGGymR4kjooTCjJ13dwufE8Y2ZnMifkYG9BTbkwff+PYV/pZTjwiXymRy3qr9uL9o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Jg5JCGD5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Jg5JCGD5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6860C4CEF1; Tue, 7 Oct 2025 21:01:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1759870901; bh=Pa4n1uj1XQRZ/idsOah9mEXaKdyFWzFzQiSdelwinD8=; h=Date:To:From:Subject:From; b=Jg5JCGD50EzTVPHu6A85KFucPSxnqDdbQV0T/EdjHW40e3bqJvyohXr7/eULKnjZ1 bQZhp2aTJRVTZVFw1GSRCWZpoaqPwEfSb//UZ1IPgnzUbtbfxuOHdQTiDS+dHn1F0o /sgX7pas8FLmqDdGHwPQwp8hha9hizhNLqCRavwg= Date: Tue, 07 Oct 2025 14:01:40 -0700 To: mm-commits@vger.kernel.org,xu.xin16@zte.com.cn,stable@vger.kernel.org,sj@kernel.org,peterx@redhat.com,miguel.ojeda.sandonis@gmail.com,david@redhat.com,chengming.zhou@linux.dev,axelrasmussen@google.com,aliceryhl@google.com,acsjakub@amazon.de,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-ksm-fix-flag-dropping-behavior-in-ksm_madvise.patch removed from -mm tree Message-Id: <20251007210141.C6860C4CEF1@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/ksm: fix flag-dropping behavior in ksm_madvise has been removed from the -mm tree. Its filename was mm-ksm-fix-flag-dropping-behavior-in-ksm_madvise.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Jakub Acs Subject: mm/ksm: fix flag-dropping behavior in ksm_madvise Date: Wed, 1 Oct 2025 09:03:52 +0000 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 NOPTI [ 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 &= ~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, using the BIT() macro. 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. [akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel] Link: https://lore.kernel.org/oe-kbuild-all/202510030449.VfSaAjvd-lkp@intel.com/ Link: https://lkml.kernel.org/r/20251001090353.57523-2-acsjakub@amazon.de Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode") Signed-off-by: Jakub Acs Signed-off-by: Miguel Ojeda Acked-by: David Hildenbrand Acked-by: SeongJae Park Tested-by: Alice Ryhl Tested-by: Miguel Ojeda Cc: Xu Xin Cc: Chengming Zhou Cc: Peter Xu Cc: Axel Rasmussen Cc: Signed-off-by: Andrew Morton --- include/linux/mm.h | 2 +- rust/bindings/bindings_helper.h | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) --- a/include/linux/mm.h~mm-ksm-fix-flag-dropping-behavior-in-ksm_madvise +++ a/include/linux/mm.h @@ -323,7 +323,7 @@ extern unsigned int kobjsize(const void #define VM_MIXEDMAP 0x10000000 /* Can contain "struct page" and pure PFN pages */ #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_MERGEABLE BIT(31) /* KSM may merge identical pages */ #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS #define VM_HIGH_ARCH_BIT_0 32 /* bit only usable on 64-bit architectures */ --- a/rust/bindings/bindings_helper.h~mm-ksm-fix-flag-dropping-behavior-in-ksm_madvise +++ a/rust/bindings/bindings_helper.h @@ -108,6 +108,7 @@ const xa_mark_t RUST_CONST_HELPER_XA_PRE const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC = XA_FLAGS_ALLOC; const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC1 = XA_FLAGS_ALLOC1; +const vm_flags_t RUST_CONST_HELPER_VM_MERGEABLE = VM_MERGEABLE; #if IS_ENABLED(CONFIG_ANDROID_BINDER_IPC_RUST) #include "../../drivers/android/binder/rust_binder.h" _ Patches currently in -mm which might be from acsjakub@amazon.de are mm-redefine-vm_-flag-constants-with-bit.patch