From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 4FE43387566 for ; Fri, 29 May 2026 17:27:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780075678; cv=none; b=IMWuYmIOQDwaPSDCrX8L7BRqWPmc+bRzSGah7ZQndolpG4XBpyHgrn3lm7oCbJMg3m+rqv3Y4CGM/7oWIX/xho0gTMxDk2fhcR89ky9P9oRytnnVgYhQbfnCnwsv173YwwG9SkimjdWYU70n4+n17Y6me74V7DsEBTzOf0K9caw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780075678; c=relaxed/simple; bh=wgQBjdRmhL1PmCnIwL5OxLFWTdzgn0xgdLKxbSOeQuQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OCr8oUp5mX4x7U1OrqKn5LBEgbqugoGRp9sF7D1sIZl/khLm09LF1zGnlYLQnyP3zKhosl+TmVP0dvtokmFR+SXzpYoFXa1MZQp1ND5sFuIg+OxmmHC4oHnDkmpTWT+ovrYJbQcEjtv9zttEBGUs+dnAuT26cinaDn9cRMyrGdg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LYykaHGE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LYykaHGE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4EEB81F0089E; Fri, 29 May 2026 17:27:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780075674; bh=1kPL22rrzi+QauahU6y1XS1epMwqoNAKDudDgPyn9b8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LYykaHGEvTd2TkD1e4znKhbj8aqcmqxNuCScLcIjCtPIoOBFAg4yIp33e+i6OEF59 xILf6BQj2cikc8EIVXA22dFndfyluB2JGCny92+8cAhC6esbQ9i4qaCdoVq9ubDIHh 8FnVQkQEMW9iG/imHkmiqSucpZVsqq9k0Ygrb0ss6hQBBHNRTsZENhcJn5vBSQ/jpO 7lede15Ko4K5BnQgfDF4jUMyNMsIi6J4InnGIQwU5qe26Ig1N7R53O0dBMXRHkMN5M KkCw4iG195iBFEkXq/QQua46YdKjOtbdaJhmRTOKbeOVe/Vh/XUf/8st3yuwpWfB1o EmVL5jo4WnnOA== Received: from phl-compute-03.internal (phl-compute-03.internal [10.202.2.43]) by mailfauth.phl.internal (Postfix) with ESMTP id AD56DF4006F; Fri, 29 May 2026 13:27:53 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Fri, 29 May 2026 13:27:53 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTGahW8s3xjZ3arjCZYsPeROx1tHGGIOxZ4ZTborx5JIY1xfx8o+3Ks6DBHpwKdcBc M0LV7UYzyw5BBW/MLyCvRpPXH4b3j/O36w1UIutGmjGoZPWXllz5NGLuWKcGXqDNqja7AN LjyibA8JUH8LlxNww+LolPBmmXeffckfCMyZ3ofUE4q+w091KUDN+vWzLN57aJjrFHnLmA DJhoBTsevLB+L7lFnUlwKPgFqlT5AUPgwhCfp483ir0podeZjRFOwVO5acGk8d/hTIZjyE iTtkTrHlenKgPfeJb7TkHTrSkVle7vVdqqUtJoKJ+Cofq6CG9ZD2U9nUSpGxcnBPWB+GWq gPC1wTp7fcejRHI3Q1FCzTHBKt9o4RKI/fN91edtIJi4rsYCqiSgf9/MN9PyG3oVtWwq2S OAwDPArj+xnGVYvnZdoZqf1pexBbR5njpxL6C3GTR+3jo1NY5djFNqneHNCwf2Hpsm15in 1XS1KK767JDo+yUy4ycjs5w9OSpF8yQaWZzTrerso3eInllVcoT5QdI3MWYQVZqkXjPL8b mUzD5UgIUZGuGJCF4hd21JivANc+J6m3AGnfZkPWlppdwuBGA0vWQZoNjowrfQO8m/0BEo x4qJqm4lDkVPvQiPUZnEnO5I6L9exiwUbCXRwfxeGYYJEZi7J5Q+cK1EffWA X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 29 May 2026 13:27:53 -0400 (EDT) From: "Kiryl Shutsemau (Meta)" To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com, pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com, sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, kernel-team@meta.com, kas@kernel.org Subject: [PATCH v6 05/15] mm: add VM_UFFD_RWP VMA flag Date: Fri, 29 May 2026 18:26:34 +0100 Message-ID: <20260529172716.357179-6-kas@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260529172716.357179-1-kas@kernel.org> References: <20260529172716.357179-1-kas@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Preparatory patch for userfaultfd read-write protection (RWP). RWP extends userfaultfd protection from plain write-protection (WP) to full read-write protection: accesses to an RWP-protected range -- reads as well as writes -- trap through userfaultfd. Reserve VM_UFFD_RWP, add the userfaultfd_rwp() and userfaultfd_protected() helpers, and wire up the smaps "ur" entry and the trace-flag table the rest of the series will use. The flag is gated on CONFIG_USERFAULTFD_RWP, which is introduced together with the UAPI in a later patch; until then VM_UFFD_RWP aliases VM_NONE and every downstream check folds to dead code. Nothing sets or queries the flag yet. Signed-off-by: Kiryl Shutsemau Assisted-by: Claude:claude-opus-4-6 Reviewed-by: Mike Rapoport (Microsoft) Reviewed-by: SeongJae Park --- Documentation/filesystems/proc.rst | 1 + fs/proc/task_mmu.c | 3 +++ include/linux/mm.h | 41 ++++++++++++++++++++---------- include/linux/userfaultfd_k.h | 32 +++++++++++++++++++---- include/trace/events/mmflags.h | 7 +++++ 5 files changed, 65 insertions(+), 19 deletions(-) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index db6167befb7b..db28207c5290 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -607,6 +607,7 @@ encoded manner. The codes are the following: um userfaultfd missing tracking uw userfaultfd wr-protect tracking ui userfaultfd minor fault + ur userfaultfd read-write-protect tracking ss shadow/guarded control stack page sl sealed lf lock on fault pages diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 939657aa334a..ca0f69b347e8 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1237,6 +1237,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR [ilog2(VM_UFFD_MINOR)] = "ui", #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ +#ifdef CONFIG_USERFAULTFD_RWP + [ilog2(VM_UFFD_RWP)] = "ur", +#endif #ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK [ilog2(VM_SHADOW_STACK)] = "ss", #endif diff --git a/include/linux/mm.h b/include/linux/mm.h index 485df9c2dbdd..5ac31fbadeef 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -353,6 +353,7 @@ enum { #endif DECLARE_VMA_BIT(UFFD_MINOR, 41), DECLARE_VMA_BIT(SEALED, 42), + DECLARE_VMA_BIT(UFFD_RWP, 43), /* Flags that reuse flags above. */ DECLARE_VMA_BIT_ALIAS(PKEY_BIT0, HIGH_ARCH_0), DECLARE_VMA_BIT_ALIAS(PKEY_BIT1, HIGH_ARCH_1), @@ -496,12 +497,17 @@ enum { #else #define VM_UFFD_MINOR VM_NONE #endif +#ifdef CONFIG_USERFAULTFD_RWP +#define VM_UFFD_RWP INIT_VM_FLAG(UFFD_RWP) +#else +#define VM_UFFD_RWP VM_NONE +#endif /* - * vma_flags_t masks for the userfaultfd VMA flags. VMA_UFFD_MINOR is gated on - * the same config as VM_UFFD_MINOR -- which implies 64BIT, where the bit fits - * -- so an out-of-range bit is never fed to mk_vma_flags() on a build whose - * bitmap cannot hold it. + * vma_flags_t masks for the userfaultfd VMA flags. The two high-bit modes are + * gated on the same configs as their VM_* flags above -- both of which imply + * 64BIT -- so an out-of-range bit is never fed to mk_vma_flags() on a build + * whose bitmap cannot hold it. */ #define VMA_UFFD_MISSING mk_vma_flags(VMA_UFFD_MISSING_BIT) #define VMA_UFFD_WP mk_vma_flags(VMA_UFFD_WP_BIT) @@ -510,6 +516,11 @@ enum { #else #define VMA_UFFD_MINOR EMPTY_VMA_FLAGS #endif +#ifdef CONFIG_USERFAULTFD_RWP +#define VMA_UFFD_RWP mk_vma_flags(VMA_UFFD_RWP_BIT) +#else +#define VMA_UFFD_RWP EMPTY_VMA_FLAGS +#endif #ifdef CONFIG_64BIT #define VM_ALLOW_ANY_UNCACHED INIT_VM_FLAG(ALLOW_ANY_UNCACHED) @@ -648,22 +659,24 @@ enum { * reconsistuted upon page fault, so necessitate page table copying upon fork. * * Note that these flags should be compared with the DESTINATION VMA not the - * source, as VM_UFFD_WP may not be propagated to destination, while all other - * flags will be. + * source: VM_UFFD_WP and VM_UFFD_RWP may be cleared on the destination + * (dup_userfaultfd() -> userfaultfd_reset_ctx() when the parent context did + * not negotiate UFFD_FEATURE_EVENT_FORK), while all other flags propagate. * * VM_PFNMAP / VM_MIXEDMAP - These contain kernel-mapped data which cannot be * reasonably reconstructed on page fault. * * VM_UFFD_WP - Encodes metadata about an installed uffd - * write protect handler, which cannot be - * reconstructed on page fault. + * VM_UFFD_RWP write- or read-write-protect handler, which + * cannot be reconstructed on page fault. * - * We always copy pgtables when dst_vma has uffd-wp - * enabled even if it's file-backed - * (e.g. shmem). Because when uffd-wp is enabled, - * pgtable contains uffd-wp protection information, - * that's something we can't retrieve from page cache, - * and skip copying will lose those info. + * We always copy pgtables when dst_vma has the + * uffd PTE bit in use even if it's file-backed + * (e.g. shmem). Because when the uffd bit is + * in use, the pgtable contains the protection + * information, that's something we can't + * retrieve from page cache, and skip copying + * will lose those info. * * VM_MAYBE_GUARD - Could contain page guard region markers which * by design are a property of the page tables diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index c4f2cc6dfcf0..f3b2db27989b 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -21,10 +21,11 @@ #include /* The set of all possible UFFD-related VM flags. */ -#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR) +#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_MINOR | \ + VM_UFFD_WP | VM_UFFD_RWP) #define __VMA_UFFD_FLAGS mk_vma_flags_from_masks(VMA_UFFD_MISSING, VMA_UFFD_WP, \ - VMA_UFFD_MINOR) + VMA_UFFD_MINOR, VMA_UFFD_RWP) /* * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining @@ -179,7 +180,8 @@ static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) { return vma_test_any_mask(vma, - mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_MINOR)); + mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_MINOR, + VMA_UFFD_RWP)); } /* @@ -210,6 +212,16 @@ static inline bool userfaultfd_minor(struct vm_area_struct *vma) return vma_test_any_mask(vma, VMA_UFFD_MINOR); } +static inline bool userfaultfd_rwp(struct vm_area_struct *vma) +{ + return vma_test_any_mask(vma, VMA_UFFD_RWP); +} + +static inline bool userfaultfd_protected(struct vm_area_struct *vma) +{ + return userfaultfd_wp(vma) || userfaultfd_rwp(vma); +} + static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma, pte_t pte) { @@ -330,6 +342,16 @@ static inline bool userfaultfd_minor(struct vm_area_struct *vma) return false; } +static inline bool userfaultfd_rwp(struct vm_area_struct *vma) +{ + return false; +} + +static inline bool userfaultfd_protected(struct vm_area_struct *vma) +{ + return false; +} + static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma, pte_t pte) { @@ -423,8 +445,8 @@ static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma) } /* - * Returns true if this is a swap pte and was uffd-wp wr-protected in either - * forms (pte marker or a normal swap pte), false otherwise. + * Returns true if this swap pte carries uffd-tracked state in either + * form (pte marker or a normal swap pte), false otherwise. */ static inline bool pte_swp_uffd_any(pte_t pte) { diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index a6e5a44c9b42..bfface3d0203 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -194,6 +194,12 @@ IF_HAVE_PG_ARCH_3(arch_3) # define IF_HAVE_UFFD_MINOR(flag, name) #endif +#ifdef CONFIG_USERFAULTFD_RWP +# define IF_HAVE_UFFD_RWP(flag, name) {flag, name}, +#else +# define IF_HAVE_UFFD_RWP(flag, name) +#endif + #if defined(CONFIG_64BIT) || defined(CONFIG_PPC32) # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name}, #else @@ -215,6 +221,7 @@ IF_HAVE_UFFD_MINOR(VM_UFFD_MINOR, "uffd_minor" ) \ {VM_PFNMAP, "pfnmap" }, \ {VM_MAYBE_GUARD, "maybe_guard" }, \ {VM_UFFD_WP, "uffd_wp" }, \ +IF_HAVE_UFFD_RWP(VM_UFFD_RWP, "uffd_rwp" ) \ {VM_LOCKED, "locked" }, \ {VM_IO, "io" }, \ {VM_SEQ_READ, "seqread" }, \ -- 2.54.0