bpf: dispatch to sleepable file dynptr

File dynptr reads may sleep when the requested folios are not in
the page cache. To avoid sleeping in non-sleepable contexts while still
supporting valid sleepable use, given that dynptrs are non-sleepable by
default, enable sleeping only when bpf_dynptr_from_file() is invoked
from a sleepable context.

This change:
  * Introduces a sleepable constructor: bpf_dynptr_from_file_sleepable()
  * Override non-sleepable constructor with sleepable if it's always
  called in sleepable context

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251026203853.135105-10-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 14f800773997b8689a554625b1981c8c0b835826..a47d67db3be5a992966423a93e763970c41754cd 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -670,6 +670,9 @@ static inline bool bpf_map_has_internal_structs(struct bpf_map *map)
 
 void bpf_map_free_internal_structs(struct bpf_map *map, void *obj);
 
+int bpf_dynptr_from_file_sleepable(struct file *file, u32 flags,
+                                  struct bpf_dynptr *ptr__uninit);
+
 extern const struct bpf_map_ops bpf_map_offload_ops;
 
 /* bpf_type_flag contains a set of flags that are applicable to the values of

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 99a7def0b978f78e212bb31884e8b198fe765f15..930e132f440fcef15343087d0a0254905b0acca1 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -4336,6 +4336,11 @@ __bpf_kfunc int bpf_dynptr_from_file(struct file *file, u32 flags, struct bpf_dy
        return make_file_dynptr(file, flags, false, (struct bpf_dynptr_kern *)ptr__uninit);
 }
 
+int bpf_dynptr_from_file_sleepable(struct file *file, u32 flags, struct bpf_dynptr *ptr__uninit)
+{
+       return make_file_dynptr(file, flags, true, (struct bpf_dynptr_kern *)ptr__uninit);
+}
+
 __bpf_kfunc int bpf_dynptr_file_discard(struct bpf_dynptr *dynptr)
 {
        struct bpf_dynptr_kern *ptr = (struct bpf_dynptr_kern *)dynptr;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 61589be91c6504f40e23855c6ad0e8ac92d4f57f..542e23fb19c7bafc613a5d9cfc361d261d783d7c 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3124,7 +3124,8 @@ struct bpf_kfunc_btf_tab {
        u32 nr_descs;
 };
 
-static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc *desc);
+static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc *desc,
+                           int insn_idx);
 
 static int kfunc_desc_cmp_by_id_off(const void *a, const void *b)
 {
@@ -21869,7 +21870,7 @@ static int fixup_call_args(struct bpf_verifier_env *env)
 }
 
 /* replace a generic kfunc with a specialized version if necessary */
-static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc *desc)
+static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc *desc, int insn_idx)
 {
        struct bpf_prog *prog = env->prog;
        bool seen_direct_write;
@@ -21904,6 +21905,9 @@ static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc
        } else if (func_id == special_kfunc_list[KF_bpf_remove_dentry_xattr]) {
                if (bpf_lsm_has_d_inode_locked(prog))
                        addr = (unsigned long)bpf_remove_dentry_xattr_locked;
+       } else if (func_id == special_kfunc_list[KF_bpf_dynptr_from_file]) {
+               if (!env->insn_aux_data[insn_idx].non_sleepable)
+                       addr = (unsigned long)bpf_dynptr_from_file_sleepable;
        }
 
 set_imm:
@@ -21963,7 +21967,7 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
                return -EFAULT;
        }
 
-       err = specialize_kfunc(env, desc);
+       err = specialize_kfunc(env, desc, insn_idx);
        if (err)
                return err;