From 6eab8f2cc6465ab093b5171ece815ec24e678d4e Mon Sep 17 00:00:00 2001 From: "Kiryl Shutsemau (Meta)" Date: Wed, 8 Jul 2026 12:14:10 +0100 Subject: userfaultfd: add UFFDIO_REGISTER_MODE_RWP and UFFDIO_RWPROTECT plumbing Add the userspace interface for read-write protection tracking: - UFFDIO_REGISTER_MODE_RWP register a range for RWP tracking - UFFD_FEATURE_RWP capability bit - UFFDIO_RWPROTECT install / remove RWP on a range Introduce CONFIG_USERFAULTFD_RWP, auto-selected on 64-bit kernels with ARCH_HAS_PTE_PROTNONE and HAVE_ARCH_USERFAULTFD_WP. The symbol gates VM_UFFD_RWP (previously aliased to VM_NONE) and the smaps/trace-flag hooks added in the preparatory patches; without it the UAPI bits added here have nothing to drive and would be unreachable. Registration sets VM_UFFD_RWP on the VMA. Combining MODE_WP with MODE_RWP is rejected because both modes claim the uffd PTE bit. UFFDIO_RWPROTECT is the bidirectional counterpart of UFFDIO_WRITEPROTECT: - MODE_RWP change_protection() with MM_CP_UFFD_RWP installs PAGE_NONE and sets the uffd bit on present PTEs - !MODE_RWP change_protection() with MM_CP_UFFD_RWP_RESOLVE restores vma->vm_page_prot and clears the bit userfaultfd_clear_vma() runs the same resolve pass on unregister so RWP state cannot outlive the uffd. Re-registering a range must not drop a mode that installs per-PTE markers (WP or RWP); doing so returns -EBUSY. This also closes a pre-existing window where re-registering without MODE_WP would strand uffd-wp markers: before, those caused extra write-faults but were otherwise benign; with RWP preservation in place, a subsequent mprotect() on a VM_UFFD_RWP VMA would silently promote the stale markers to RWP. The feature is not yet advertised. UFFDIO_REGISTER_MODE_RWP, UFFD_FEATURE_RWP, and _UFFDIO_RWPROTECT are intentionally absent from UFFD_API_REGISTER_MODES, UFFD_API_FEATURES, and UFFD_API_RANGE_IOCTLS, so UFFDIO_API masks them out and the register-mode validator rejects the bit. The follow-up patch adds fault dispatch and exposes the UAPI. Link: https://lore.kernel.org/20260708111417.173443-10-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau Assisted-by: Claude:claude-opus-4-6 Reviewed-by: Mike Rapoport (Microsoft) Cc: Andrea Arcangeli Cc: David Hildenbrand Cc: James Houghton Cc: Jonathan Corbet Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Paolo Bonzini Cc: Peter Xu Cc: Sean Christopherson Cc: SeongJae Park Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Zi Yan Signed-off-by: Andrew Morton --- include/uapi/linux/userfaultfd.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h index 2841e4ea8f2c..7b78aa3b5318 100644 --- a/include/uapi/linux/userfaultfd.h +++ b/include/uapi/linux/userfaultfd.h @@ -79,6 +79,7 @@ #define _UFFDIO_WRITEPROTECT (0x06) #define _UFFDIO_CONTINUE (0x07) #define _UFFDIO_POISON (0x08) +#define _UFFDIO_RWPROTECT (0x09) #define _UFFDIO_API (0x3F) /* userfaultfd ioctl ids */ @@ -103,6 +104,8 @@ struct uffdio_continue) #define UFFDIO_POISON _IOWR(UFFDIO, _UFFDIO_POISON, \ struct uffdio_poison) +#define UFFDIO_RWPROTECT _IOWR(UFFDIO, _UFFDIO_RWPROTECT, \ + struct uffdio_rwprotect) /* read() structure */ struct uffd_msg { @@ -158,6 +161,7 @@ struct uffd_msg { #define UFFD_PAGEFAULT_FLAG_WRITE (1<<0) /* If this was a write fault */ #define UFFD_PAGEFAULT_FLAG_WP (1<<1) /* If reason is VM_UFFD_WP */ #define UFFD_PAGEFAULT_FLAG_MINOR (1<<2) /* If reason is VM_UFFD_MINOR */ +#define UFFD_PAGEFAULT_FLAG_RWP (1<<3) /* If reason is VM_UFFD_RWP */ struct uffdio_api { /* userland asks for an API number and the features to enable */ @@ -230,6 +234,11 @@ struct uffdio_api { * * UFFD_FEATURE_MOVE indicates that the kernel supports moving an * existing page contents from userspace. + * + * UFFD_FEATURE_RWP indicates that the kernel supports + * UFFDIO_REGISTER_MODE_RWP for read-write protection tracking. + * Pages are made inaccessible via UFFDIO_RWPROTECT and faults + * are delivered when the pages are re-accessed. */ #define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0) #define UFFD_FEATURE_EVENT_FORK (1<<1) @@ -248,6 +257,7 @@ struct uffdio_api { #define UFFD_FEATURE_POISON (1<<14) #define UFFD_FEATURE_WP_ASYNC (1<<15) #define UFFD_FEATURE_MOVE (1<<16) +#define UFFD_FEATURE_RWP (1<<17) __u64 features; __u64 ioctls; @@ -263,6 +273,7 @@ struct uffdio_register { #define UFFDIO_REGISTER_MODE_MISSING ((__u64)1<<0) #define UFFDIO_REGISTER_MODE_WP ((__u64)1<<1) #define UFFDIO_REGISTER_MODE_MINOR ((__u64)1<<2) +#define UFFDIO_REGISTER_MODE_RWP ((__u64)1<<3) __u64 mode; /* @@ -356,6 +367,14 @@ struct uffdio_poison { __s64 updated; }; +struct uffdio_rwprotect { + struct uffdio_range range; + /* !RWP means undo RWP-protection */ +#define UFFDIO_RWPROTECT_MODE_RWP ((__u64)1<<0) +#define UFFDIO_RWPROTECT_MODE_DONTWAKE ((__u64)1<<1) + __u64 mode; +}; + struct uffdio_move { __u64 dst; __u64 src; -- cgit v1.2.3