diff mbox series

[bpf-next,RFC,v1,1/8] bpf: Introduce BPF support for kernel module function calls

Message ID 20210830173424.1385796-2-memxor@gmail.com
State New
Headers show
Series [bpf-next,RFC,v1,1/8] bpf: Introduce BPF support for kernel module function calls | expand

Commit Message

Kumar Kartikeya Dwivedi Aug. 30, 2021, 5:34 p.m. UTC 
This change adds support on the kernel side to allow for BPF programs to
call kernel module functions. Userspace will prepare an array of module
BTF fds that is passed in during BPF_PROG_LOAD. In the kernel, the
module BTF array is placed in the auxilliary struct for bpf_prog.

The verifier then uses insn->off to index into this table. insn->off is
used by subtracting one from it, as userspace has to set the index of
array in insn->off incremented by 1. This lets us denote vmlinux btf by
insn->off == 0, and the prog->aux->kfunc_btf_tab[insn->off - 1] for
module BTFs.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h            |  1 +
 include/linux/filter.h         |  9 ++++
 include/uapi/linux/bpf.h       |  3 +-
 kernel/bpf/core.c              | 14 ++++++
 kernel/bpf/syscall.c           | 55 +++++++++++++++++++++-
 kernel/bpf/verifier.c          | 85 ++++++++++++++++++++++++++--------
 tools/include/uapi/linux/bpf.h |  3 +-
 7 files changed, 147 insertions(+), 23 deletions(-)

Comments

Alexei Starovoitov Aug. 30, 2021, 8:01 p.m. UTC | #1 
On Mon, Aug 30, 2021 at 11:04:17PM +0530, Kumar Kartikeya Dwivedi wrote:
> This change adds support on the kernel side to allow for BPF programs to
> call kernel module functions. Userspace will prepare an array of module
> BTF fds that is passed in during BPF_PROG_LOAD. In the kernel, the
> module BTF array is placed in the auxilliary struct for bpf_prog.
> 
> The verifier then uses insn->off to index into this table. insn->off is
> used by subtracting one from it, as userspace has to set the index of
> array in insn->off incremented by 1. This lets us denote vmlinux btf by
> insn->off == 0, and the prog->aux->kfunc_btf_tab[insn->off - 1] for
> module BTFs.
> 
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  include/linux/bpf.h            |  1 +
>  include/linux/filter.h         |  9 ++++
>  include/uapi/linux/bpf.h       |  3 +-
>  kernel/bpf/core.c              | 14 ++++++
>  kernel/bpf/syscall.c           | 55 +++++++++++++++++++++-
>  kernel/bpf/verifier.c          | 85 ++++++++++++++++++++++++++--------
>  tools/include/uapi/linux/bpf.h |  3 +-
>  7 files changed, 147 insertions(+), 23 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f4c16f19f83e..39f59e5f3a26 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -874,6 +874,7 @@ struct bpf_prog_aux {
>  	void *jit_data; /* JIT specific data. arch dependent */
>  	struct bpf_jit_poke_descriptor *poke_tab;
>  	struct bpf_kfunc_desc_tab *kfunc_tab;
> +	struct bpf_kfunc_btf_tab *kfunc_btf_tab;
>  	u32 size_poke_tab;
>  	struct bpf_ksym ksym;
>  	const struct bpf_prog_ops *ops;
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 7d248941ecea..46451891633d 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -592,6 +592,15 @@ struct bpf_prog {
>  	struct bpf_insn		insnsi[];
>  };
>  
> +#define MAX_KFUNC_DESCS 256
> +/* There can only be at most MAX_KFUNC_DESCS module BTFs for kernel module
> + * function calls.
> + */
> +struct bpf_kfunc_btf_tab {
> +	u32 nr_btfs;
> +	struct btf_mod_pair btfs[];
> +};
> +
>  struct sk_filter {
>  	refcount_t	refcnt;
>  	struct rcu_head	rcu;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 791f31dd0abe..4cbb2082a553 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1334,8 +1334,9 @@ union bpf_attr {
>  			/* or valid module BTF object fd or 0 to attach to vmlinux */
>  			__u32		attach_btf_obj_fd;
>  		};
> -		__u32		:32;		/* pad */
> +		__u32		kfunc_btf_fds_cnt; /* reuse hole for count of BTF fds below */

No need for size.

>  		__aligned_u64	fd_array;	/* array of FDs */
> +		__aligned_u64   kfunc_btf_fds;  /* array of BTF FDs for module kfunc support */

Just reuse fd_array. No need for another array of FDs.

> +		tab = prog->aux->kfunc_btf_tab;
> +		for (i = 0; i < n; i++) {
> +			struct btf_mod_pair *p;
> +			struct btf *mod_btf;
> +
> +			mod_btf = btf_get_by_fd(fds[i]);
> +			if (IS_ERR(mod_btf)) {
> +				err = PTR_ERR(mod_btf);
> +				goto free_prog;
> +			}
> +			if (!btf_is_module(mod_btf)) {
> +				err = -EINVAL;
> +				btf_put(mod_btf);
> +				goto free_prog;
> +			}

just do that dynamically like access to fd_array is handled in other places.
no need to preload.
diff mbox series

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f4c16f19f83e..39f59e5f3a26 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -874,6 +874,7 @@  struct bpf_prog_aux {
 	void *jit_data; /* JIT specific data. arch dependent */
 	struct bpf_jit_poke_descriptor *poke_tab;
 	struct bpf_kfunc_desc_tab *kfunc_tab;
+	struct bpf_kfunc_btf_tab *kfunc_btf_tab;
 	u32 size_poke_tab;
 	struct bpf_ksym ksym;
 	const struct bpf_prog_ops *ops;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 7d248941ecea..46451891633d 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -592,6 +592,15 @@  struct bpf_prog {
 	struct bpf_insn		insnsi[];
 };
 
+#define MAX_KFUNC_DESCS 256
+/* There can only be at most MAX_KFUNC_DESCS module BTFs for kernel module
+ * function calls.
+ */
+struct bpf_kfunc_btf_tab {
+	u32 nr_btfs;
+	struct btf_mod_pair btfs[];
+};
+
 struct sk_filter {
 	refcount_t	refcnt;
 	struct rcu_head	rcu;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 791f31dd0abe..4cbb2082a553 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1334,8 +1334,9 @@  union bpf_attr {
 			/* or valid module BTF object fd or 0 to attach to vmlinux */
 			__u32		attach_btf_obj_fd;
 		};
-		__u32		:32;		/* pad */
+		__u32		kfunc_btf_fds_cnt; /* reuse hole for count of BTF fds below */
 		__aligned_u64	fd_array;	/* array of FDs */
+		__aligned_u64   kfunc_btf_fds;  /* array of BTF FDs for module kfunc support */
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_* commands */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9f4636d021b1..73ba6d862df3 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2249,12 +2249,26 @@  static void bpf_free_used_btfs(struct bpf_prog_aux *aux)
 	kfree(aux->used_btfs);
 }
 
+static void bpf_free_kfunc_btf_tab(struct bpf_prog_aux *aux)
+{
+	struct bpf_kfunc_btf_tab *tab = aux->kfunc_btf_tab;
+
+	if (tab) {
+		while (tab->nr_btfs--) {
+			module_put(tab->btfs[tab->nr_btfs].module);
+			btf_put(tab->btfs[tab->nr_btfs].btf);
+		}
+		kfree(tab);
+	}
+}
+
 static void bpf_prog_free_deferred(struct work_struct *work)
 {
 	struct bpf_prog_aux *aux;
 	int i;
 
 	aux = container_of(work, struct bpf_prog_aux, work);
+	bpf_free_kfunc_btf_tab(aux);
 	bpf_free_used_maps(aux);
 	bpf_free_used_btfs(aux);
 	if (bpf_prog_is_dev_bound(aux))
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4e50c0bfdb7d..bbbd664b2872 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2156,16 +2156,16 @@  static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
 }
 
 /* last field in 'union bpf_attr' used by this command */
-#define	BPF_PROG_LOAD_LAST_FIELD fd_array
+#define	BPF_PROG_LOAD_LAST_FIELD kfunc_btf_fds
 
 static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
 {
 	enum bpf_prog_type type = attr->prog_type;
 	struct bpf_prog *prog, *dst_prog = NULL;
 	struct btf *attach_btf = NULL;
-	int err;
 	char license[128];
 	bool is_gpl;
+	int err;
 
 	if (CHECK_ATTR(BPF_PROG_LOAD))
 		return -EINVAL;
@@ -2204,6 +2204,8 @@  static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
 		return -EPERM;
 	if (is_perfmon_prog_type(type) && !perfmon_capable())
 		return -EPERM;
+	if (attr->kfunc_btf_fds_cnt > MAX_KFUNC_DESCS)
+		return -E2BIG;
 
 	/* attach_prog_fd/attach_btf_obj_fd can specify fd of either bpf_prog
 	 * or btf, we need to check which one it is
@@ -2254,6 +2256,55 @@  static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
 		return -ENOMEM;
 	}
 
+	if (attr->kfunc_btf_fds_cnt) {
+		struct bpf_kfunc_btf_tab *tab;
+		int fds[MAX_KFUNC_DESCS], i;
+		bpfptr_t kfunc_btf_fds;
+		u32 kfunc_btf_size, n;
+
+		kfunc_btf_size = min_t(u32, MAX_KFUNC_DESCS, attr->kfunc_btf_fds_cnt);
+		kfunc_btf_fds = make_bpfptr(attr->kfunc_btf_fds, uattr.is_kernel);
+
+		err = -EFAULT;
+		if (copy_from_bpfptr(fds, kfunc_btf_fds, kfunc_btf_size * sizeof(int)))
+			goto free_prog;
+
+		err = -ENOMEM;
+
+		n = kfunc_btf_size;
+		kfunc_btf_size *= sizeof(prog->aux->kfunc_btf_tab->btfs[0]);
+		kfunc_btf_size += sizeof(*prog->aux->kfunc_btf_tab);
+		prog->aux->kfunc_btf_tab = kzalloc(kfunc_btf_size, GFP_KERNEL);
+		if (!prog->aux->kfunc_btf_tab)
+			goto free_prog;
+
+		tab = prog->aux->kfunc_btf_tab;
+		for (i = 0; i < n; i++) {
+			struct btf_mod_pair *p;
+			struct btf *mod_btf;
+
+			mod_btf = btf_get_by_fd(fds[i]);
+			if (IS_ERR(mod_btf)) {
+				err = PTR_ERR(mod_btf);
+				goto free_prog;
+			}
+			if (!btf_is_module(mod_btf)) {
+				err = -EINVAL;
+				btf_put(mod_btf);
+				goto free_prog;
+			}
+
+			p = &tab->btfs[tab->nr_btfs];
+			p->module = btf_try_get_module(mod_btf);
+			if (!p->module) {
+				btf_put(mod_btf);
+				goto free_prog;
+			}
+			p->btf = mod_btf;
+			tab->nr_btfs++;
+		}
+	}
+
 	prog->expected_attach_type = attr->expected_attach_type;
 	prog->aux->attach_btf = attach_btf;
 	prog->aux->attach_btf_id = attr->attach_btf_id;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 206c221453cf..de0670a8b1df 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1632,7 +1632,6 @@  struct bpf_kfunc_desc {
 	s32 imm;
 };
 
-#define MAX_KFUNC_DESCS 256
 struct bpf_kfunc_desc_tab {
 	struct bpf_kfunc_desc descs[MAX_KFUNC_DESCS];
 	u32 nr_descs;
@@ -1660,13 +1659,45 @@  find_kfunc_desc(const struct bpf_prog *prog, u32 func_id)
 		       sizeof(tab->descs[0]), kfunc_desc_cmp_by_id);
 }
 
-static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
+static struct btf *find_kfunc_desc_btf(struct bpf_verifier_env *env,
+				       u32 func_id, s16 offset)
+{
+	struct bpf_kfunc_btf_tab *btf_tab;
+
+	btf_tab = env->prog->aux->kfunc_btf_tab;
+	/* offset can be MAX_KFUNC_DESCS, since index into the array is offset - 1,
+	 * as we reserve offset == 0 for btf_vmlinux
+	 */
+	if (offset < 0 || offset > MAX_KFUNC_DESCS) {
+		verbose(env, "offset %d is incorrect for kernel function call\n", (int)offset);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (offset) {
+		if (!btf_tab) {
+			verbose(env,
+				"offset %d for kfunc call but no kernel module BTFs passed\n",
+				(int)offset);
+			return ERR_PTR(-EINVAL);
+		} else if (offset > btf_tab->nr_btfs) {
+			verbose(env,
+				"offset %d incorrect for module BTF array with %u descriptors\n",
+				(int)offset, btf_tab->nr_btfs);
+			return ERR_PTR(-EINVAL);
+		}
+		return btf_tab->btfs[offset - 1].btf;
+	}
+	return btf_vmlinux ?: ERR_PTR(-ENOENT);
+}
+
+static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 {
 	const struct btf_type *func, *func_proto;
 	struct bpf_kfunc_desc_tab *tab;
 	struct bpf_prog_aux *prog_aux;
 	struct bpf_kfunc_desc *desc;
 	const char *func_name;
+	struct btf *desc_btf;
 	unsigned long addr;
 	int err;
 
@@ -1699,6 +1730,12 @@  static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
 		prog_aux->kfunc_tab = tab;
 	}
 
+	desc_btf = find_kfunc_desc_btf(env, func_id, offset);
+	if (IS_ERR(desc_btf)) {
+		verbose(env, "failed to find BTF for kernel function\n");
+		return PTR_ERR(desc_btf);
+	}
+
 	if (find_kfunc_desc(env->prog, func_id))
 		return 0;
 
@@ -1707,20 +1744,20 @@  static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
 		return -E2BIG;
 	}
 
-	func = btf_type_by_id(btf_vmlinux, func_id);
+	func = btf_type_by_id(desc_btf, func_id);
 	if (!func || !btf_type_is_func(func)) {
 		verbose(env, "kernel btf_id %u is not a function\n",
 			func_id);
 		return -EINVAL;
 	}
-	func_proto = btf_type_by_id(btf_vmlinux, func->type);
+	func_proto = btf_type_by_id(desc_btf, func->type);
 	if (!func_proto || !btf_type_is_func_proto(func_proto)) {
 		verbose(env, "kernel function btf_id %u does not have a valid func_proto\n",
 			func_id);
 		return -EINVAL;
 	}
 
-	func_name = btf_name_by_offset(btf_vmlinux, func->name_off);
+	func_name = btf_name_by_offset(desc_btf, func->name_off);
 	addr = kallsyms_lookup_name(func_name);
 	if (!addr) {
 		verbose(env, "cannot find address for kernel function %s\n",
@@ -1731,7 +1768,7 @@  static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id)
 	desc = &tab->descs[tab->nr_descs++];
 	desc->func_id = func_id;
 	desc->imm = BPF_CAST_CALL(addr) - __bpf_call_base;
-	err = btf_distill_func_proto(&env->log, btf_vmlinux,
+	err = btf_distill_func_proto(&env->log, desc_btf,
 				     func_proto, func_name,
 				     &desc->func_model);
 	if (!err)
@@ -1815,7 +1852,7 @@  static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
 		} else if (bpf_pseudo_call(insn)) {
 			ret = add_subprog(env, i + insn->imm + 1);
 		} else {
-			ret = add_kfunc_call(env, insn->imm);
+			ret = add_kfunc_call(env, insn->imm, insn->off);
 		}
 
 		if (ret < 0)
@@ -2152,12 +2189,17 @@  static int get_prev_insn_idx(struct bpf_verifier_state *st, int i,
 static const char *disasm_kfunc_name(void *data, const struct bpf_insn *insn)
 {
 	const struct btf_type *func;
+	struct btf *desc_btf;
 
 	if (insn->src_reg != BPF_PSEUDO_KFUNC_CALL)
 		return NULL;
 
-	func = btf_type_by_id(btf_vmlinux, insn->imm);
-	return btf_name_by_offset(btf_vmlinux, func->name_off);
+	desc_btf = find_kfunc_desc_btf(data, insn->imm, insn->off);
+	if (IS_ERR(desc_btf))
+		return "<error>";
+
+	func = btf_type_by_id(desc_btf, insn->imm);
+	return btf_name_by_offset(desc_btf, func->name_off);
 }
 
 /* For given verifier state backtrack_insn() is called from the last insn to
@@ -6482,12 +6524,17 @@  static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	const char *func_name, *ptr_type_name;
 	u32 i, nargs, func_id, ptr_type_id;
 	const struct btf_param *args;
+	struct btf *desc_btf;
 	int err;
 
+	desc_btf = find_kfunc_desc_btf(env, insn->imm, insn->off);
+	if (IS_ERR(desc_btf))
+		return PTR_ERR(desc_btf);
+
 	func_id = insn->imm;
-	func = btf_type_by_id(btf_vmlinux, func_id);
-	func_name = btf_name_by_offset(btf_vmlinux, func->name_off);
-	func_proto = btf_type_by_id(btf_vmlinux, func->type);
+	func = btf_type_by_id(desc_btf, func_id);
+	func_name = btf_name_by_offset(desc_btf, func->name_off);
+	func_proto = btf_type_by_id(desc_btf, func->type);
 
 	if (!env->ops->check_kfunc_call ||
 	    !env->ops->check_kfunc_call(func_id)) {
@@ -6497,7 +6544,7 @@  static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	}
 
 	/* Check the arguments */
-	err = btf_check_kfunc_arg_match(env, btf_vmlinux, func_id, regs);
+	err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs);
 	if (err)
 		return err;
 
@@ -6505,15 +6552,15 @@  static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 		mark_reg_not_init(env, regs, caller_saved[i]);
 
 	/* Check return type */
-	t = btf_type_skip_modifiers(btf_vmlinux, func_proto->type, NULL);
+	t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
 	if (btf_type_is_scalar(t)) {
 		mark_reg_unknown(env, regs, BPF_REG_0);
 		mark_btf_func_reg_size(env, BPF_REG_0, t->size);
 	} else if (btf_type_is_ptr(t)) {
-		ptr_type = btf_type_skip_modifiers(btf_vmlinux, t->type,
+		ptr_type = btf_type_skip_modifiers(desc_btf, t->type,
 						   &ptr_type_id);
 		if (!btf_type_is_struct(ptr_type)) {
-			ptr_type_name = btf_name_by_offset(btf_vmlinux,
+			ptr_type_name = btf_name_by_offset(desc_btf,
 							   ptr_type->name_off);
 			verbose(env, "kernel function %s returns pointer type %s %s is not supported\n",
 				func_name, btf_type_str(ptr_type),
@@ -6521,7 +6568,7 @@  static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			return -EINVAL;
 		}
 		mark_reg_known_zero(env, regs, BPF_REG_0);
-		regs[BPF_REG_0].btf = btf_vmlinux;
+		regs[BPF_REG_0].btf = desc_btf;
 		regs[BPF_REG_0].type = PTR_TO_BTF_ID;
 		regs[BPF_REG_0].btf_id = ptr_type_id;
 		mark_btf_func_reg_size(env, BPF_REG_0, sizeof(void *));
@@ -6532,7 +6579,7 @@  static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	for (i = 0; i < nargs; i++) {
 		u32 regno = i + 1;
 
-		t = btf_type_skip_modifiers(btf_vmlinux, args[i].type, NULL);
+		t = btf_type_skip_modifiers(desc_btf, args[i].type, NULL);
 		if (btf_type_is_ptr(t))
 			mark_btf_func_reg_size(env, regno, sizeof(void *));
 		else
@@ -11070,7 +11117,6 @@  static int do_check(struct bpf_verifier_env *env)
 			env->jmps_processed++;
 			if (opcode == BPF_CALL) {
 				if (BPF_SRC(insn->code) != BPF_K ||
-				    insn->off != 0 ||
 				    (insn->src_reg != BPF_REG_0 &&
 				     insn->src_reg != BPF_PSEUDO_CALL &&
 				     insn->src_reg != BPF_PSEUDO_KFUNC_CALL) ||
@@ -12425,6 +12471,7 @@  static int jit_subprogs(struct bpf_verifier_env *env)
 		func[i]->aux->stack_depth = env->subprog_info[i].stack_depth;
 		func[i]->jit_requested = 1;
 		func[i]->aux->kfunc_tab = prog->aux->kfunc_tab;
+		func[i]->aux->kfunc_btf_tab = prog->aux->kfunc_btf_tab;
 		func[i]->aux->linfo = prog->aux->linfo;
 		func[i]->aux->nr_linfo = prog->aux->nr_linfo;
 		func[i]->aux->jited_linfo = prog->aux->jited_linfo;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 791f31dd0abe..4cbb2082a553 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1334,8 +1334,9 @@  union bpf_attr {
 			/* or valid module BTF object fd or 0 to attach to vmlinux */
 			__u32		attach_btf_obj_fd;
 		};
-		__u32		:32;		/* pad */
+		__u32		kfunc_btf_fds_cnt; /* reuse hole for count of BTF fds below */
 		__aligned_u64	fd_array;	/* array of FDs */
+		__aligned_u64   kfunc_btf_fds;  /* array of BTF FDs for module kfunc support */
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_* commands */