Commit 720e6a43 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
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bpf: Allow struct argument in trampoline based programs 



Allow struct argument in trampoline based programs where
the struct size should be <= 16 bytes. In such cases, the argument
will be put into up to 2 registers for bpf, x86_64 and arm64
architectures.

To support arch-specific trampoline manipulation,
add arg_flags for additional struct information about arguments
in btf_func_model. Such information will be used in arch specific
function arch_prepare_bpf_trampoline() to prepare argument access
properly in trampoline.

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220831152646.2078089-1-yhs@fb.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 1e660f7e

include/linux/bpf.h

+4 −0
Original line number Diff line number Diff line
@@ -727,10 +727,14 @@ enum bpf_cgroup_storage_type { 
 */

#define MAX_BPF_FUNC_REG_ARGS 5



/* The argument is a structure. */

#define BTF_FMODEL_STRUCT_ARG		BIT(0)



struct btf_func_model {

	u8 ret_size;

	u8 nr_args;

	u8 arg_size[MAX_BPF_FUNC_ARGS];

	u8 arg_flags[MAX_BPF_FUNC_ARGS];

};



/* Restore arguments before returning from trampoline to let original function

kernel/bpf/btf.c

+39 −6
Original line number Diff line number Diff line
@@ -5328,6 +5328,34 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t) 
	return btf_type_is_int(t);

}



static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,

			   int off)

{

	const struct btf_param *args;

	const struct btf_type *t;

	u32 offset = 0, nr_args;

	int i;



	if (!func_proto)

		return off / 8;



	nr_args = btf_type_vlen(func_proto);

	args = (const struct btf_param *)(func_proto + 1);

	for (i = 0; i < nr_args; i++) {

		t = btf_type_skip_modifiers(btf, args[i].type, NULL);

		offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);

		if (off < offset)

			return i;

	}



	t = btf_type_skip_modifiers(btf, func_proto->type, NULL);

	offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);

	if (off < offset)

		return nr_args;



	return nr_args + 1;

}



bool btf_ctx_access(int off, int size, enum bpf_access_type type,

		    const struct bpf_prog *prog,

		    struct bpf_insn_access_aux *info)
@@ -5347,7 +5375,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, 
			tname, off);

		return false;

	}

	arg = off / 8;

	arg = get_ctx_arg_idx(btf, t, off);

	args = (const struct btf_param *)(t + 1);

	/* if (t == NULL) Fall back to default BPF prog with

	 * MAX_BPF_FUNC_REG_ARGS u64 arguments.
@@ -5417,7 +5445,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, 
	/* skip modifiers */

	while (btf_type_is_modifier(t))

		t = btf_type_by_id(btf, t->type);

	if (btf_type_is_small_int(t) || btf_is_any_enum(t))

	if (btf_type_is_small_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))

		/* accessing a scalar */

		return true;

	if (!btf_type_is_ptr(t)) {
@@ -5881,7 +5909,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id, 
	if (btf_type_is_ptr(t))

		/* kernel size of pointer. Not BPF's size of pointer*/

		return sizeof(void *);

	if (btf_type_is_int(t) || btf_is_any_enum(t))

	if (btf_type_is_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))

		return t->size;

	return -EINVAL;

}
@@ -5901,8 +5929,10 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, 
		/* BTF function prototype doesn't match the verifier types.

		 * Fall back to MAX_BPF_FUNC_REG_ARGS u64 args.

		 */

		for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++)

		for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++) {

			m->arg_size[i] = 8;

			m->arg_flags[i] = 0;

		}

		m->ret_size = 8;

		m->nr_args = MAX_BPF_FUNC_REG_ARGS;

		return 0;
@@ -5916,7 +5946,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, 
		return -EINVAL;

	}

	ret = __get_type_size(btf, func->type, &t);

	if (ret < 0) {

	if (ret < 0 || __btf_type_is_struct(t)) {

		bpf_log(log,

			"The function %s return type %s is unsupported.\n",

			tname, btf_kind_str[BTF_INFO_KIND(t->info)]);
@@ -5932,7 +5962,9 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, 
			return -EINVAL;

		}

		ret = __get_type_size(btf, args[i].type, &t);

		if (ret < 0) {



		/* No support of struct argument size greater than 16 bytes */

		if (ret < 0 || ret > 16) {

			bpf_log(log,

				"The function %s arg%d type %s is unsupported.\n",

				tname, i, btf_kind_str[BTF_INFO_KIND(t->info)]);
@@ -5945,6 +5977,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, 
			return -EINVAL;

		}

		m->arg_size[i] = ret;

		m->arg_flags[i] = __btf_type_is_struct(t) ? BTF_FMODEL_STRUCT_ARG : 0;

	}

	m->nr_args = nargs;

	return 0;