This patch adds a new helper function
void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len);
which returns a pointer to the underlying data of a dynptr. *len*
must be a statically known value. The bpf program may access the returned
data slice as a normal buffer (eg can do direct reads and writes), since
the verifier associates the length with the returned pointer, and
enforces that no out of bounds accesses occur.
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 12 ++++++++++++
kernel/bpf/helpers.c | 28 ++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 23 +++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 12 ++++++++++++
5 files changed, 76 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 60dac491065e..e46cb1b2a90f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -488,6 +488,7 @@ enum bpf_return_type {
RET_PTR_TO_TCP_SOCK_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_TCP_SOCK,
RET_PTR_TO_SOCK_COMMON_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_SOCK_COMMON,
RET_PTR_TO_ALLOC_MEM_OR_NULL = PTR_MAYBE_NULL | MEM_ALLOC | RET_PTR_TO_ALLOC_MEM,
+ RET_PTR_TO_DYNPTR_MEM_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_ALLOC_MEM,
RET_PTR_TO_BTF_ID_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_BTF_ID,
/* This must be the last entry. Its purpose is to ensure the enum is
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index efe2505650e6..f4009dbdf62d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5238,6 +5238,17 @@ union bpf_attr {
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
* is a read-only dynptr.
+ *
+ * void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
+ * Description
+ * Get a pointer to the underlying dynptr data.
+ *
+ * *len* must be a statically known value. The returned data slice
+ * is invalidated whenever the dynptr is invalidated.
+ * Return
+ * Pointer to the underlying dynptr data, NULL if the dynptr is
+ * read-only, if the dynptr is invalid, or if the offset and length
+ * is out of bounds.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5443,6 +5454,7 @@ union bpf_attr {
FN(ringbuf_discard_dynptr), \
FN(dynptr_read), \
FN(dynptr_write), \
+ FN(dynptr_data), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8cef3fb0d143..225806a02efb 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1549,6 +1549,32 @@ const struct bpf_func_proto bpf_dynptr_write_proto = {
.arg4_type = ARG_CONST_SIZE_OR_ZERO,
};
+BPF_CALL_3(bpf_dynptr_data, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
+{
+ int err;
+
+ if (!ptr->data)
+ return 0;
+
+ err = bpf_dynptr_check_off_len(ptr, offset, len);
+ if (err)
+ return 0;
+
+ if (bpf_dynptr_is_rdonly(ptr))
+ return 0;
+
+ return (unsigned long)(ptr->data + ptr->offset + offset);
+}
+
+const struct bpf_func_proto bpf_dynptr_data_proto = {
+ .func = bpf_dynptr_data,
+ .gpl_only = false,
+ .ret_type = RET_PTR_TO_DYNPTR_MEM_OR_NULL,
+ .arg1_type = ARG_PTR_TO_DYNPTR,
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
+};
+
const struct bpf_func_proto bpf_get_current_task_proto __weak;
const struct bpf_func_proto bpf_get_current_task_btf_proto __weak;
const struct bpf_func_proto bpf_probe_read_user_proto __weak;
@@ -1615,6 +1641,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
return &bpf_dynptr_read_proto;
case BPF_FUNC_dynptr_write:
return &bpf_dynptr_write_proto;
+ case BPF_FUNC_dynptr_data:
+ return &bpf_dynptr_data_proto;
default:
break;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a94b8211e34d..71355a74cd82 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5832,6 +5832,14 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
return __check_ptr_off_reg(env, reg, regno, fixed_off_ok);
}
+static u32 stack_slot_get_id(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+ struct bpf_func_state *state = func(env, reg);
+ int spi = get_spi(reg->off);
+
+ return state->stack[spi].spilled_ptr.id;
+}
+
static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
struct bpf_call_arg_meta *meta,
const struct bpf_func_proto *fn)
@@ -7384,6 +7392,21 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
regs[BPF_REG_0].id = id;
/* For release_reference() */
regs[BPF_REG_0].ref_obj_id = id;
+ } else if (func_id == BPF_FUNC_dynptr_data) {
+ int dynptr_id = 0, i;
+
+ /* Find the id of the dynptr we're acquiring a reference to */
+ for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++) {
+ if (arg_type_is_dynptr(fn->arg_type[i])) {
+ if (dynptr_id) {
+ verbose(env, "verifier internal error: multiple dynptr args in func\n");
+ return -EFAULT;
+ }
+ dynptr_id = stack_slot_get_id(env, ®s[BPF_REG_1 + i]);
+ }
+ }
+ /* For release_reference() */
+ regs[BPF_REG_0].ref_obj_id = dynptr_id;
}
do_refine_retval_range(regs, fn->ret_type, func_id, &meta);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index efe2505650e6..f4009dbdf62d 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5238,6 +5238,17 @@ union bpf_attr {
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
* is a read-only dynptr.
+ *
+ * void *bpf_dynptr_data(struct bpf_dynptr *ptr, u32 offset, u32 len)
+ * Description
+ * Get a pointer to the underlying dynptr data.
+ *
+ * *len* must be a statically known value. The returned data slice
+ * is invalidated whenever the dynptr is invalidated.
+ * Return
+ * Pointer to the underlying dynptr data, NULL if the dynptr is
+ * read-only, if the dynptr is invalid, or if the offset and length
+ * is out of bounds.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5443,6 +5454,7 @@ union bpf_attr {
FN(ringbuf_discard_dynptr), \
FN(dynptr_read), \
FN(dynptr_write), \
+ FN(dynptr_data), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.30.2
