btf: Allow dynamic pointer parameters in kfuncs

Allow dynamic pointers (struct bpf_dynptr_kern *) to be specified as
parameters in kfuncs. Also, ensure that dynamic pointers passed as argument
are valid and initialized, are a pointer to the stack, and of the type
local. More dynamic pointer types can be supported in the future.

To properly detect whether a parameter is of the desired type, introduce
the stringify_struct() macro to compare the returned structure name with
the desired name. In addition, protect against structure renames, by
halting the build with BUILD_BUG_ON(), so that developers have to revisit
the code.

To check if a dynamic pointer passed to the kfunc is valid and initialized,
and if its type is local, export the existing functions
is_dynptr_reg_valid_init() and is_dynptr_type_expected().

Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220920075951.929132-5-roberto.sassu@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index e197f8f..9e1e696 100644 (file)
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -593,6 +593,11 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
                             u32 regno);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
                   u32 regno, u32 mem_size);
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
+                             struct bpf_reg_state *reg);
+bool is_dynptr_type_expected(struct bpf_verifier_env *env,
+                            struct bpf_reg_state *reg,
+                            enum bpf_arg_type arg_type);
 
 /* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
 static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 1fcc833..f9aabab 100644 (file)
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -52,6 +52,15 @@
 #define KF_SLEEPABLE    (1 << 5) /* kfunc may sleep */
 #define KF_DESTRUCTIVE  (1 << 6) /* kfunc performs destructive actions */
 
+/*
+ * Return the name of the passed struct, if exists, or halt the build if for
+ * example the structure gets renamed. In this way, developers have to revisit
+ * the code using that structure name, and update it accordingly.
+ */
+#define stringify_struct(x)                    \
+       ({ BUILD_BUG_ON(sizeof(struct x) < 0);  \
+          __stringify(x); })
+
 struct btf;
 struct btf_member;
 struct btf_type;

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dbcf020..13faede 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6449,15 +6449,20 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
                        if (is_kfunc) {
                                bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
+                               bool arg_dynptr = btf_type_is_struct(ref_t) &&
+                                                 !strcmp(ref_tname,
+                                                         stringify_struct(bpf_dynptr_kern));
 
                                /* Permit pointer to mem, but only when argument
                                 * type is pointer to scalar, or struct composed
                                 * (recursively) of scalars.
                                 * When arg_mem_size is true, the pointer can be
                                 * void *.
+                                * Also permit initialized local dynamic pointers.
                                 */
                                if (!btf_type_is_scalar(ref_t) &&
                                    !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
+                                   !arg_dynptr &&
                                    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
                                        bpf_log(log,
                                                "arg#%d pointer type %s %s must point to %sscalar, or struct with scalar\n",
@@ -6465,6 +6470,34 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
                                        return -EINVAL;
                                }
 
+                               if (arg_dynptr) {
+                                       if (reg->type != PTR_TO_STACK) {
+                                               bpf_log(log, "arg#%d pointer type %s %s not to stack\n",
+                                                       i, btf_type_str(ref_t),
+                                                       ref_tname);
+                                               return -EINVAL;
+                                       }
+
+                                       if (!is_dynptr_reg_valid_init(env, reg)) {
+                                               bpf_log(log,
+                                                       "arg#%d pointer type %s %s must be valid and initialized\n",
+                                                       i, btf_type_str(ref_t),
+                                                       ref_tname);
+                                               return -EINVAL;
+                                       }
+
+                                       if (!is_dynptr_type_expected(env, reg,
+                                                       ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL)) {
+                                               bpf_log(log,
+                                                       "arg#%d pointer type %s %s points to unsupported dynamic pointer type\n",
+                                                       i, btf_type_str(ref_t),
+                                                       ref_tname);
+                                               return -EINVAL;
+                                       }
+
+                                       continue;
+                               }
+
                                /* Check for mem, len pair */
                                if (arg_mem_size) {
                                        if (check_kfunc_mem_size_reg(env, &regs[regno + 1], regno + 1)) {

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c08dde1..6f6d2d5 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -782,8 +782,8 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
        return true;
 }
 
-static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
-                                    struct bpf_reg_state *reg)
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
+                             struct bpf_reg_state *reg)
 {
        struct bpf_func_state *state = func(env, reg);
        int spi = get_spi(reg->off);
@@ -802,9 +802,9 @@ static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
        return true;
 }
 
-static bool is_dynptr_type_expected(struct bpf_verifier_env *env,
-                                   struct bpf_reg_state *reg,
-                                   enum bpf_arg_type arg_type)
+bool is_dynptr_type_expected(struct bpf_verifier_env *env,
+                            struct bpf_reg_state *reg,
+                            enum bpf_arg_type arg_type)
 {
        struct bpf_func_state *state = func(env, reg);
        enum bpf_dynptr_type dynptr_type;