leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

bpf: Add btf_struct_ids_match function

Browse Source 
Adding btf_struct_ids_match function to check if given address provided
by BTF object + offset is also address of another nested BTF object.

This allows to pass an argument to helper, which is defined via parent
BTF object + offset, like for bpf_d_path (added in following changes):

  SEC("fentry/filp_close")
  int BPF_PROG(prog_close, struct file *file, void *id)
  {
    ...
    ret = bpf_d_path(&file->f_path, ...

The first bpf_d_path argument is hold by verifier as BTF file object
plus offset of f_path member.

The btf_struct_ids_match function will walk the struct file object and
check if there's nested struct path object on the given offset.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-9-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2020-08-25 21:21:18 +02:00 committed by Alexei Starovoitov
parent 1c6d28a6ac
commit faaf4a790d
3 changed files with 44 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/bpf.h
View File

@ -1358,6 +1358,8 @@ int btf_struct_access(struct bpf_verifier_log *log,
const struct btf_type *t, int off, int size,
enum bpf_access_type atype,
u32 *next_btf_id);
bool btf_struct_ids_match(struct bpf_verifier_log *log,
int off, u32 id, u32 need_type_id);
int btf_resolve_helper_id(struct bpf_verifier_log *log,
const struct bpf_func_proto *fn, int);

31
kernel/bpf/btf.c
View File

@ -4160,6 +4160,37 @@ int btf_struct_access(struct bpf_verifier_log *log,
return -EINVAL;
}
bool btf_struct_ids_match(struct bpf_verifier_log *log,
int off, u32 id, u32 need_type_id)
{
const struct btf_type *type;
int err;
/* Are we already done? */
if (need_type_id == id && off == 0)
return true;
again:
type = btf_type_by_id(btf_vmlinux, id);
if (!type)
return false;
err = btf_struct_walk(log, type, off, 1, &id);
if (err != WALK_STRUCT)
return false;
/* We found nested struct object. If it matches
* the requested ID, we're done. Otherwise let's
* continue the search with offset 0 in the new
* type.
*/
if (need_type_id != id) {
off = 0;
goto again;
}
return true;
}
int btf_resolve_helper_id(struct bpf_verifier_log *log,
const struct bpf_func_proto *fn, int arg)
{

17
kernel/bpf/verifier.c
View File

@ -3995,16 +3995,21 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
goto err_type;
}
} else if (arg_type == ARG_PTR_TO_BTF_ID) {
bool ids_match = false;
expected_type = PTR_TO_BTF_ID;
if (type != expected_type)
goto err_type;
if (!fn->check_btf_id) {
if (reg->btf_id != meta->btf_id) {
verbose(env, "Helper has type %s got %s in R%d\n",
kernel_type_name(meta->btf_id),
kernel_type_name(reg->btf_id), regno);
return -EACCES;
ids_match = btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
meta->btf_id);
if (!ids_match) {
verbose(env, "Helper has type %s got %s in R%d\n",
kernel_type_name(meta->btf_id),
kernel_type_name(reg->btf_id), regno);
return -EACCES;
}
}
} else if (!fn->check_btf_id(reg->btf_id, arg)) {
verbose(env, "Helper does not support %s in R%d\n",
@ -4012,7 +4017,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
return -EACCES;
}
if (!tnum_is_const(reg->var_off) || reg->var_off.value || reg->off) {
if ((reg->off && !ids_match) || !tnum_is_const(reg->var_off) || reg->var_off.value) {
verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
regno);
return -EACCES;