[PATCH v3 04/16] mm: add VM_UFFD_RWP VMA flag
Kiryl Shutsemau <[email protected]>
| Newsgroups | org.kernel.vger.linux-man,org.kernel.vger.kvm,org.kernel.vger.linux-doc,org.kernel.vger.linux-kernel,org.kernel.vger.linux-kselftest,org.kvack.linux-mm |
|---|---|
| Message-ID | <[email protected]> |
From: "Kiryl Shutsemau (Meta)" <[email protected]> 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 <[email protected]> Assisted-by: Claude:claude-opus-4-6 Reviewed-by: Mike Rapoport (Microsoft) <[email protected]> Reviewed-by: SeongJae Park <[email protected]> --- Documentation/filesystems/proc.rst | 1 + fs/proc/task_mmu.c | 3 +++ include/linux/mm.h | 28 ++++++++++++++++--------- include/linux/userfaultfd_k.h | 33 ++++++++++++++++++++++++------ include/trace/events/mmflags.h | 7 +++++++ 5 files changed, 56 insertions(+), 16 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 5827074962e7..fbaede228201 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1206,6 +1206,9 @@ 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 0b776907152e..3f53d1e978c0 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), @@ -496,6 +497,11 @@ 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 #ifdef CONFIG_64BIT #define VM_ALLOW_ANY_UNCACHED INIT_VM_FLAG(ALLOW_ANY_UNCACHED) #define VM_SEALED INIT_VM_FLAG(SEALED) @@ -633,22 +639,24 @@ 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 98f546e83cd2..889c7b45fec8 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -21,10 +21,11 @@ #include <linux/hugetlb_inline.h> /* 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(VMA_UFFD_MISSING_BIT, VMA_UFFD_WP_BIT, \ - VMA_UFFD_MINOR_BIT) +#define __VMA_UFFD_FLAGS mk_vma_flags(VMA_UFFD_MISSING_BIT, VMA_UFFD_MINOR_BIT, \ + VMA_UFFD_WP_BIT, VMA_UFFD_RWP_BIT) /* * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining @@ -192,7 +193,7 @@ 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->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); + return vma->vm_flags & (VM_UFFD_MINOR | VM_UFFD_WP | VM_UFFD_RWP); } /* @@ -222,6 +223,16 @@ static inline bool userfaultfd_minor(struct vm_area_struct *vma) return vma->vm_flags & VM_UFFD_MINOR; } +static inline bool userfaultfd_rwp(struct vm_area_struct *vma) +{ + return vma->vm_flags & VM_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) { @@ -364,6 +375,16 @@ 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) { @@ -457,8 +478,8 @@ 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" }, \ -- 2.51.2