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([140.174.215.70]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4a779e90ffasm4502441cf.70.2025.06.19.20.11.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jun 2025 20:11:38 -0700 (PDT) From: Emil Tsalapatis To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, memxor@gmail.com, sched-ext@meta.com, Emil Tsalapatis Subject: [PATCH bpf-next 1/2] bpf/arena: add bpf_arena_guard_pages kfunc Date: Thu, 19 Jun 2025 23:11:17 -0400 Message-ID: <20250620031118.245601-2-emil@etsalapatis.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250620031118.245601-1-emil@etsalapatis.com> References: <20250620031118.245601-1-emil@etsalapatis.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a new BPF arena kfunc from protecting a range of pages. These pages cannot be allocated, either explicitly through bpf_arena_alloc_pages() or implicitly through userspace page faults. Signed-off-by: Emil Tsalapatis --- kernel/bpf/arena.c | 95 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 92 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c index 0d56cea71602..2f9293eb7151 100644 --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -48,6 +48,7 @@ struct bpf_arena { u64 user_vm_end; struct vm_struct *kern_vm; struct range_tree rt; + struct range_tree rt_guard; struct list_head vma_list; struct mutex lock; }; @@ -143,6 +144,20 @@ static struct bpf_map *arena_map_alloc(union bpf_attr *attr) bpf_map_area_free(arena); goto err; } + + /* + * Use the same semantics as the main range tree to reuse + * its methods: Present ranges are all unguarded, while + * absent ones are guarded. + */ + range_tree_init(&arena->rt_guard); + err = range_tree_set(&arena->rt_guard, 0, attr->max_entries); + if (err) { + range_tree_destroy(&arena->rt); + bpf_map_area_free(arena); + goto err; + } + mutex_init(&arena->lock); return &arena->map; @@ -193,6 +208,7 @@ static void arena_map_free(struct bpf_map *map) apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena), KERN_VM_SZ - GUARD_SZ, existing_page_cb, NULL); free_vm_area(arena->kern_vm); + range_tree_destroy(&arena->rt_guard); range_tree_destroy(&arena->rt); bpf_map_area_free(arena); } @@ -282,6 +298,11 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf) /* User space requested to segfault when page is not allocated by bpf prog */ return VM_FAULT_SIGSEGV; + /* Make sure the page is not guarded. */ + ret = is_range_tree_set(&arena->rt_guard, vmf->pgoff, 1); + if (ret) + return VM_FAULT_SIGSEGV; + ret = range_tree_clear(&arena->rt, vmf->pgoff, 1); if (ret) return VM_FAULT_SIGSEGV; @@ -456,12 +477,17 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt ret = is_range_tree_set(&arena->rt, pgoff, page_cnt); if (ret) goto out_free_pages; - ret = range_tree_clear(&arena->rt, pgoff, page_cnt); } else { ret = pgoff = range_tree_find(&arena->rt, page_cnt); - if (pgoff >= 0) - ret = range_tree_clear(&arena->rt, pgoff, page_cnt); + if (pgoff < 0) + goto out_free_pages; } + + ret = is_range_tree_set(&arena->rt_guard, pgoff, page_cnt); + if (ret) + goto out_free_pages; + + ret = range_tree_clear(&arena->rt, pgoff, page_cnt); if (ret) goto out_free_pages; @@ -512,6 +538,7 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt) u64 full_uaddr, uaddr_end; long kaddr, pgoff, i; struct page *page; + int ret; /* only aligned lower 32-bit are relevant */ uaddr = (u32)uaddr; @@ -525,7 +552,14 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt) guard(mutex)(&arena->lock); + pgoff = compute_pgoff(arena, uaddr); + + /* Do not free regions that include guarded pages. */ + ret = is_range_tree_set(&arena->rt_guard, pgoff, page_cnt); + if (ret) + return; + /* clear range */ range_tree_set(&arena->rt, pgoff, page_cnt); @@ -550,6 +584,46 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt) } } +static int arena_guard_pages(struct bpf_arena *arena, long uaddr, u32 page_cnt) +{ + long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT; + long pgoff; + int ret; + + if (uaddr & ~PAGE_MASK) + return 0; + + pgoff = compute_pgoff(arena, uaddr); + if (pgoff + page_cnt > page_cnt_max) + return -EINVAL; + + guard(mutex)(&arena->lock); + + /* Make sure we have not already guarded the pages. */ + ret = is_range_tree_set(&arena->rt_guard, pgoff, page_cnt); + if (ret) + return -EALREADY; + + /* Cannot guard already allocated pages. */ + ret = is_range_tree_set(&arena->rt, pgoff, page_cnt); + if (ret) + return -EINVAL; + + /* Reserve the region. */ + ret = range_tree_clear(&arena->rt_guard, pgoff, page_cnt); + if (ret) + return ret; + + /* Also "allocate" the region to prevent it from being allocated. */ + ret = range_tree_clear(&arena->rt, pgoff, page_cnt); + if (ret) { + range_tree_set(&arena->rt_guard, pgoff, page_cnt); + return ret; + } + + return 0; +} + __bpf_kfunc_start_defs(); __bpf_kfunc void *bpf_arena_alloc_pages(void *p__map, void *addr__ign, u32 page_cnt, @@ -573,11 +647,26 @@ __bpf_kfunc void bpf_arena_free_pages(void *p__map, void *ptr__ign, u32 page_cnt return; arena_free_pages(arena, (long)ptr__ign, page_cnt); } + +__bpf_kfunc int bpf_arena_guard_pages(void *p__map, void *ptr__ign, u32 page_cnt) +{ + struct bpf_map *map = p__map; + struct bpf_arena *arena = container_of(map, struct bpf_arena, map); + + if (map->map_type != BPF_MAP_TYPE_ARENA) + return -EINVAL; + + if (!page_cnt) + return 0; + + return arena_guard_pages(arena, (long)ptr__ign, page_cnt); +} __bpf_kfunc_end_defs(); BTF_KFUNCS_START(arena_kfuncs) BTF_ID_FLAGS(func, bpf_arena_alloc_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_RET | KF_ARENA_ARG2) BTF_ID_FLAGS(func, bpf_arena_free_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_ARG2) +BTF_ID_FLAGS(func, bpf_arena_guard_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_ARG2) BTF_KFUNCS_END(arena_kfuncs) static const struct btf_kfunc_id_set common_kfunc_set = { -- 2.49.0