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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: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220831152646.2078089-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2022-08-31 08:26:46 -07:00 committed by Alexei Starovoitov
parent 1e660f7ebe
commit 720e6a4351
2 changed files with 43 additions and 6 deletions
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4
include/linux/bpf.h
View File

@ -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

45
kernel/bpf/btf.c
View File

@ -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;