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bpf: Support bpf_kptr_xchg into local kptr

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Currently, users can only stash kptr into map values with bpf_kptr_xchg().
This patch further supports stashing kptr into local kptr by adding local
kptr as a valid destination type.

When stashing into local kptr, btf_record in program BTF is used instead
of btf_record in map to search for the btf_field of the local kptr.

The local kptr specific checks in check_reg_type() only apply when the
source argument of bpf_kptr_xchg() is local kptr. Therefore, we make the
scope of the check explicit as the destination now can also be local kptr.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Amery Hung <amery.hung@bytedance.com>
Link: https://lore.kernel.org/r/20240813212424.2871455-5-amery.hung@bytedance.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Marchevsky
2024-08-13 21:24:23 +00:00
committed by Alexei Starovoitov
parent d59232afb0
commit b0966c7245
3 changed files with 37 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/uapi/linux/bpf.h
+5 -4
View File
@@ -5519,11 +5519,12 @@ union bpf_attr {
* **-EOPNOTSUPP** if the hash calculation failed or **-EINVAL** if
* invalid arguments are passed.
*
* void *bpf_kptr_xchg(void *map_value, void *ptr)
* void *bpf_kptr_xchg(void *dst, void *ptr)
* Description
* Exchange kptr at pointer *map_value* with *ptr*, and return the
* old value. *ptr* can be NULL, otherwise it must be a referenced
* pointer which will be released when this helper is called.
* Exchange kptr at pointer *dst* with *ptr*, and return the old value.
* *dst* can be map value or local kptr. *ptr* can be NULL, otherwise
* it must be a referenced pointer which will be released when this helper
* is called.
* Return
* The old value of kptr (which can be NULL). The returned pointer
* if not NULL, is a reference which must be released using its
kernel/bpf/helpers.c
+2 -2
View File
@@ -1619,9 +1619,9 @@ void bpf_wq_cancel_and_free(void *val)
schedule_work(&work->delete_work);
}
BPF_CALL_2(bpf_kptr_xchg, void *, map_value, void *, ptr)
BPF_CALL_2(bpf_kptr_xchg, void *, dst, void *, ptr)
{
unsigned long *kptr = map_value;
unsigned long *kptr = dst;
/* This helper may be inlined by verifier. */
return xchg(kptr, (unsigned long)ptr);
kernel/bpf/verifier.c
+30 -14
View File
@@ -7803,29 +7803,38 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
struct bpf_call_arg_meta *meta)
{
struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
struct bpf_map *map_ptr = reg->map_ptr;
struct btf_field *kptr_field;
struct bpf_map *map_ptr;
struct btf_record *rec;
u32 kptr_off;
if (type_is_ptr_alloc_obj(reg->type)) {
rec = reg_btf_record(reg);
} else { /* PTR_TO_MAP_VALUE */
map_ptr = reg->map_ptr;
if (!map_ptr->btf) {
verbose(env, "map '%s' has to have BTF in order to use bpf_kptr_xchg\n",
map_ptr->name);
return -EINVAL;
}
rec = map_ptr->record;
meta->map_ptr = map_ptr;
}
if (!tnum_is_const(reg->var_off)) {
verbose(env,
"R%d doesn't have constant offset. kptr has to be at the constant offset\n",
regno);
return -EINVAL;
}
if (!map_ptr->btf) {
verbose(env, "map '%s' has to have BTF in order to use bpf_kptr_xchg\n",
map_ptr->name);
return -EINVAL;
}
if (!btf_record_has_field(map_ptr->record, BPF_KPTR)) {
verbose(env, "map '%s' has no valid kptr\n", map_ptr->name);
if (!btf_record_has_field(rec, BPF_KPTR)) {
verbose(env, "R%d has no valid kptr\n", regno);
return -EINVAL;
}
meta->map_ptr = map_ptr;
kptr_off = reg->off + reg->var_off.value;
kptr_field = btf_record_find(map_ptr->record, kptr_off, BPF_KPTR);
kptr_field = btf_record_find(rec, kptr_off, BPF_KPTR);
if (!kptr_field) {
verbose(env, "off=%d doesn't point to kptr\n", kptr_off);
return -EACCES;
@@ -8412,7 +8421,12 @@ static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
static const struct bpf_reg_types const_str_ptr_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types timer_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types kptr_xchg_dest_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types kptr_xchg_dest_types = {
.types = {
PTR_TO_MAP_VALUE,
PTR_TO_BTF_ID | MEM_ALLOC
}
};
static const struct bpf_reg_types dynptr_types = {
.types = {
PTR_TO_STACK,
@@ -8483,7 +8497,8 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
if (base_type(arg_type) == ARG_PTR_TO_MEM)
type &= ~DYNPTR_TYPE_FLAG_MASK;
if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type)) {
/* Local kptr types are allowed as the source argument of bpf_kptr_xchg */
if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type) && regno == BPF_REG_2) {
type &= ~MEM_ALLOC;
type &= ~MEM_PERCPU;
}
@@ -8576,7 +8591,8 @@ found:
verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n");
return -EFAULT;
}
if (meta->func_id == BPF_FUNC_kptr_xchg) {
/* Check if local kptr in src arg matches kptr in dst arg */
if (meta->func_id == BPF_FUNC_kptr_xchg && regno == BPF_REG_2) {
if (map_kptr_match_type(env, meta->kptr_field, reg, regno))
return -EACCES;
}
@@ -8887,7 +8903,7 @@ skip_type_check:
meta->release_regno = regno;
}
if (reg->ref_obj_id) {
if (reg->ref_obj_id && base_type(arg_type) != ARG_KPTR_XCHG_DEST) {
if (meta->ref_obj_id) {
verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
regno, reg->ref_obj_id,