Commit b8d31762 authored by Roberto Sassu's avatar Roberto Sassu Committed by Alexei Starovoitov
Browse files

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: default avatarRoberto Sassu <roberto.sassu@huawei.com>
Acked-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220920075951.929132-5-roberto.sassu@huaweicloud.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent e9e315b4

include/linux/bpf_verifier.h

+5 −0
Original line number Diff line number Diff line
@@ -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,

include/linux/btf.h

+9 −0
Original line number Diff line number Diff line
@@ -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;

kernel/bpf/btf.c

+33 −0
Original line number Diff line number Diff line
@@ -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)) {

kernel/bpf/verifier.c

+5 −5
Original line number Diff line number Diff line
@@ -782,7 +782,7 @@ 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,

bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,

			      struct bpf_reg_state *reg)

{

	struct bpf_func_state *state = func(env, reg);
@@ -802,7 +802,7 @@ 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,

bool is_dynptr_type_expected(struct bpf_verifier_env *env,

			     struct bpf_reg_state *reg,

			     enum bpf_arg_type arg_type)

{