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

bpf: Add a kfunc to type cast from bpf uapi ctx to kernel ctx

Browse Source 
Implement bpf_cast_to_kern_ctx() kfunc which does a type cast
of a uapi ctx object to the corresponding kernel ctx. Previously
if users want to access some data available in kctx but not
in uapi ctx, bpf_probe_read_kernel() helper is needed.
The introduction of bpf_cast_to_kern_ctx() allows direct
memory access which makes code simpler and easier to understand.

Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221120195432.3113982-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song
2022-11-20 11:54:32 -08:00
committed by Alexei Starovoitov
parent cfe1456440
commit fd264ca020
4 changed files with 53 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
kernel/bpf/verifier.c
View File

@@ -7907,6 +7907,7 @@ struct bpf_kfunc_call_arg_meta {
u32 ref_obj_id;
u8 release_regno;
bool r0_rdonly;
u32 ret_btf_id;
u64 r0_size;
struct {
u64 value;
@@ -8151,6 +8152,7 @@ enum special_kfunc_type {
KF_bpf_list_push_back,
KF_bpf_list_pop_front,
KF_bpf_list_pop_back,
KF_bpf_cast_to_kern_ctx,
};
BTF_SET_START(special_kfunc_set)
@@ -8160,6 +8162,7 @@ BTF_ID(func, bpf_list_push_front)
BTF_ID(func, bpf_list_push_back)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_cast_to_kern_ctx)
BTF_SET_END(special_kfunc_set)
BTF_ID_LIST(special_kfunc_list)
@@ -8169,6 +8172,7 @@ BTF_ID(func, bpf_list_push_front)
BTF_ID(func, bpf_list_push_back)
BTF_ID(func, bpf_list_pop_front)
BTF_ID(func, bpf_list_pop_back)
BTF_ID(func, bpf_cast_to_kern_ctx)
static enum kfunc_ptr_arg_type
get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
@@ -8182,6 +8186,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
struct bpf_reg_state *reg = &regs[regno];
bool arg_mem_size = false;
if (meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx])
return KF_ARG_PTR_TO_CTX;
/* In this function, we verify the kfunc's BTF as per the argument type,
* leaving the rest of the verification with respect to the register
* type to our caller. When a set of conditions hold in the BTF type of
@@ -8668,6 +8675,13 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
verbose(env, "arg#%d expected pointer to ctx, but got %s\n", i, btf_type_str(t));
return -EINVAL;
}
if (meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx]) {
ret = get_kern_ctx_btf_id(&env->log, resolve_prog_type(env->prog));
if (ret < 0)
return -EINVAL;
meta->ret_btf_id = ret;
}
break;
case KF_ARG_PTR_TO_ALLOC_BTF_ID:
if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) {
@@ -8922,6 +8936,11 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
regs[BPF_REG_0].btf = field->list_head.btf;
regs[BPF_REG_0].btf_id = field->list_head.value_btf_id;
regs[BPF_REG_0].off = field->list_head.node_offset;
} else if (meta.func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx]) {
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].type = PTR_TO_BTF_ID | PTR_TRUSTED;
regs[BPF_REG_0].btf = desc_btf;
regs[BPF_REG_0].btf_id = meta.ret_btf_id;
} else {
verbose(env, "kernel function %s unhandled dynamic return type\n",
meta.func_name);
@@ -15175,6 +15194,9 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
insn_buf[1] = addr[1];
insn_buf[2] = *insn;
*cnt = 3;
} else if (desc->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx]) {
insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
*cnt = 1;
}
return 0;
}