bpf: Allow calls to arena functions while holding spinlocks

The bpf_arena_*_pages() kfuncs can be called from sleepable contexts,
but the verifier still prevents BPF programs from calling them while
holding a spinlock. Amend the verifier to allow for BPF programs
calling arena page management functions while holding a lock.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260106-arena-under-lock-v2-2-378e9eab3066@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7f82e27dd7e7c3e8328a5c4aa629b79db2dbe03f..53635ea2e41bb6cc64eaf84eab805aaedf1cba31 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12373,6 +12373,7 @@ enum special_kfunc_type {
        KF_bpf_task_work_schedule_resume_impl,
        KF_bpf_arena_alloc_pages,
        KF_bpf_arena_free_pages,
+       KF_bpf_arena_reserve_pages,
 };
 
 BTF_ID_LIST(special_kfunc_list)
@@ -12449,6 +12450,7 @@ BTF_ID(func, bpf_task_work_schedule_signal_impl)
 BTF_ID(func, bpf_task_work_schedule_resume_impl)
 BTF_ID(func, bpf_arena_alloc_pages)
 BTF_ID(func, bpf_arena_free_pages)
+BTF_ID(func, bpf_arena_reserve_pages)
 
 static bool is_task_work_add_kfunc(u32 func_id)
 {
@@ -12884,10 +12886,17 @@ static bool is_bpf_res_spin_lock_kfunc(u32 btf_id)
               btf_id == special_kfunc_list[KF_bpf_res_spin_unlock_irqrestore];
 }
 
+static bool is_bpf_arena_kfunc(u32 btf_id)
+{
+       return btf_id == special_kfunc_list[KF_bpf_arena_alloc_pages] ||
+              btf_id == special_kfunc_list[KF_bpf_arena_free_pages] ||
+              btf_id == special_kfunc_list[KF_bpf_arena_reserve_pages];
+}
+
 static bool kfunc_spin_allowed(u32 btf_id)
 {
        return is_bpf_graph_api_kfunc(btf_id) || is_bpf_iter_num_api_kfunc(btf_id) ||
-              is_bpf_res_spin_lock_kfunc(btf_id);
+              is_bpf_res_spin_lock_kfunc(btf_id) || is_bpf_arena_kfunc(btf_id);
 }
 
 static bool is_sync_callback_calling_kfunc(u32 btf_id)