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bpf: Support __uptr type tag in BTF

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This patch introduces the "__uptr" type tag to BTF. It is to define
a pointer pointing to the user space memory. This patch adds BTF
logic to pass the "__uptr" type tag.

btf_find_kptr() is reused for the "__uptr" tag. The "__uptr" will only
be supported in the map_value of the task storage map. However,
btf_parse_struct_meta() also uses btf_find_kptr() but it is not
interested in "__uptr". This patch adds a "field_mask" argument
to btf_find_kptr() which will return BTF_FIELD_IGNORE if the
caller is not interested in a “__uptr” field.

btf_parse_kptr() is also reused to parse the uptr.
The btf_check_and_fixup_fields() is changed to do extra
checks on the uptr to ensure that its struct size is not larger
than PAGE_SIZE. It is not clear how a uptr pointing to a CO-RE
supported kernel struct will be used, so it is also not allowed now.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20241023234759.860539-2-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kui-Feng Lee
2024-10-23 16:47:48 -07:00
committed by Alexei Starovoitov
parent 39b8ab1519
commit 1cb80d9e93
3 changed files with 36 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/bpf.h
View File

@@ -203,6 +203,7 @@ enum btf_field_type {
BPF_GRAPH_ROOT = BPF_RB_ROOT | BPF_LIST_HEAD,
BPF_REFCOUNT = (1 << 9),
BPF_WORKQUEUE = (1 << 10),
BPF_UPTR = (1 << 11),
};
typedef void (*btf_dtor_kfunc_t)(void *);
@@ -322,6 +323,8 @@ static inline const char *btf_field_type_name(enum btf_field_type type)
return "kptr";
case BPF_KPTR_PERCPU:
return "percpu_kptr";
case BPF_UPTR:
return "uptr";
case BPF_LIST_HEAD:
return "bpf_list_head";
case BPF_LIST_NODE:
@@ -350,6 +353,7 @@ static inline u32 btf_field_type_size(enum btf_field_type type)
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
return sizeof(u64);
case BPF_LIST_HEAD:
return sizeof(struct bpf_list_head);
@@ -379,6 +383,7 @@ static inline u32 btf_field_type_align(enum btf_field_type type)
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
return __alignof__(u64);
case BPF_LIST_HEAD:
return __alignof__(struct bpf_list_head);

34
kernel/bpf/btf.c
View File

@@ -3334,7 +3334,7 @@ static int btf_find_struct(const struct btf *btf, const struct btf_type *t,
}
static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
u32 off, int sz, struct btf_field_info *info)
u32 off, int sz, struct btf_field_info *info, u32 field_mask)
{
enum btf_field_type type;
u32 res_id;
@@ -3358,9 +3358,14 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
type = BPF_KPTR_REF;
else if (!strcmp("percpu_kptr", __btf_name_by_offset(btf, t->name_off)))
type = BPF_KPTR_PERCPU;
else if (!strcmp("uptr", __btf_name_by_offset(btf, t->name_off)))
type = BPF_UPTR;
else
return -EINVAL;
if (!(type & field_mask))
return BTF_FIELD_IGNORE;
/* Get the base type */
t = btf_type_skip_modifiers(btf, t->type, &res_id);
/* Only pointer to struct is allowed */
@@ -3502,7 +3507,7 @@ static int btf_get_field_type(const struct btf *btf, const struct btf_type *var_
field_mask_test_name(BPF_REFCOUNT, "bpf_refcount");
/* Only return BPF_KPTR when all other types with matchable names fail */
if (field_mask & BPF_KPTR && !__btf_type_is_struct(var_type)) {
if (field_mask & (BPF_KPTR | BPF_UPTR) && !__btf_type_is_struct(var_type)) {
type = BPF_KPTR_REF;
goto end;
}
@@ -3535,6 +3540,7 @@ static int btf_repeat_fields(struct btf_field_info *info,
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
case BPF_LIST_HEAD:
case BPF_RB_ROOT:
break;
@@ -3661,8 +3667,9 @@ static int btf_find_field_one(const struct btf *btf,
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
ret = btf_find_kptr(btf, var_type, off, sz,
info_cnt ? &info[0] : &tmp);
info_cnt ? &info[0] : &tmp, field_mask);
if (ret < 0)
return ret;
break;
@@ -3985,6 +3992,7 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
ret = btf_parse_kptr(btf, &rec->fields[i], &info_arr[i]);
if (ret < 0)
goto end;
@@ -4044,12 +4052,28 @@ int btf_check_and_fixup_fields(const struct btf *btf, struct btf_record *rec)
* Hence we only need to ensure that bpf_{list_head,rb_root} ownership
* does not form cycles.
*/
if (IS_ERR_OR_NULL(rec) || !(rec->field_mask & BPF_GRAPH_ROOT))
if (IS_ERR_OR_NULL(rec) || !(rec->field_mask & (BPF_GRAPH_ROOT | BPF_UPTR)))
return 0;
for (i = 0; i < rec->cnt; i++) {
struct btf_struct_meta *meta;
const struct btf_type *t;
u32 btf_id;
if (rec->fields[i].type == BPF_UPTR) {
/* The uptr only supports pinning one page and cannot
* point to a kernel struct
*/
if (btf_is_kernel(rec->fields[i].kptr.btf))
return -EINVAL;
t = btf_type_by_id(rec->fields[i].kptr.btf,
rec->fields[i].kptr.btf_id);
if (!t->size)
return -EINVAL;
if (t->size > PAGE_SIZE)
return -E2BIG;
continue;
}
if (!(rec->fields[i].type & BPF_GRAPH_ROOT))
continue;
btf_id = rec->fields[i].graph_root.value_btf_id;
@@ -5560,7 +5584,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
goto free_aof;
}
ret = btf_find_kptr(btf, t, 0, 0, &tmp);
ret = btf_find_kptr(btf, t, 0, 0, &tmp, BPF_KPTR);
if (ret != BTF_FIELD_FOUND)
continue;

2
kernel/bpf/syscall.c
View File

@@ -548,6 +548,7 @@ void btf_record_free(struct btf_record *rec)
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
if (rec->fields[i].kptr.module)
module_put(rec->fields[i].kptr.module);
if (btf_is_kernel(rec->fields[i].kptr.btf))
@@ -597,6 +598,7 @@ struct btf_record *btf_record_dup(const struct btf_record *rec)
case BPF_KPTR_UNREF:
case BPF_KPTR_REF:
case BPF_KPTR_PERCPU:
case BPF_UPTR:
if (btf_is_kernel(fields[i].kptr.btf))
btf_get(fields[i].kptr.btf);
if (fields[i].kptr.module && !try_module_get(fields[i].kptr.module)) {