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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 17D6940013 X-Rspamd-Server: rspam03 X-Stat-Signature: us7kayp6ru9zohb5q8dmm96c4zxcn4e1 X-HE-Tag: 1780075676-567093 X-HE-Meta: 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 hWapfACX WNgHKGL86nYr1OfNGjxFMiN5ZRKuFEkizwFahZ2VsYQWNqpmfIamcDXke7oG+K0MDJ110FwCuHpWN/Y5aMeCvgIKPNmX4Ghgjz5XEpfNjp0QOwva3ztvCSgO6IS72KVEVLHRpilcIJnSsWxPCaMjX70FtPwUQ8a5ZcrL6QUZ90TIQbxgbpOnkc8xptQoh+MxD86q3OIdh74EWeS6z8H+W16Lva0z/sTkcir7z20R42x8kQKBodVobQIs1f/F0+ZjyLWpFbHQeXmBCMy+f1+4Tv7BZTcKfVxHImugepvr0TonJZouzos4GIhJQHA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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