bpf: Make per_cpu_ptr return rdonly PTR_TO_MEM.
Tag the return type of {per, this}_cpu_ptr with RDONLY_MEM. The
returned value of this pair of helpers is kernel object, which
can not be updated by bpf programs. Previously these two helpers
return PTR_OT_MEM for kernel objects of scalar type, which allows
one to directly modify the memory. Now with RDONLY_MEM tagging,
the verifier will reject programs that write into RDONLY_MEM.
Fixes: 63d9b80dcf2c ("bpf: Introducte bpf_this_cpu_ptr()")
Fixes: eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
Fixes: 4976b718c355 ("bpf: Introduce pseudo_btf_id")
Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211217003152.48334-8-haoluo@google.com
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index c49dc5c..6a65e2a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -682,7 +682,7 @@
const struct bpf_func_proto bpf_per_cpu_ptr_proto = {
.func = bpf_per_cpu_ptr,
.gpl_only = false,
- .ret_type = RET_PTR_TO_MEM_OR_BTF_ID | PTR_MAYBE_NULL,
+ .ret_type = RET_PTR_TO_MEM_OR_BTF_ID | PTR_MAYBE_NULL | MEM_RDONLY,
.arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,
.arg2_type = ARG_ANYTHING,
};
@@ -695,7 +695,7 @@
const struct bpf_func_proto bpf_this_cpu_ptr_proto = {
.func = bpf_this_cpu_ptr,
.gpl_only = false,
- .ret_type = RET_PTR_TO_MEM_OR_BTF_ID,
+ .ret_type = RET_PTR_TO_MEM_OR_BTF_ID | MEM_RDONLY,
.arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,
};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9073337..f49b3d3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4399,15 +4399,30 @@
mark_reg_unknown(env, regs, value_regno);
}
}
- } else if (reg->type == PTR_TO_MEM) {
+ } else if (base_type(reg->type) == PTR_TO_MEM) {
+ bool rdonly_mem = type_is_rdonly_mem(reg->type);
+
+ if (type_may_be_null(reg->type)) {
+ verbose(env, "R%d invalid mem access '%s'\n", regno,
+ reg_type_str(env, reg->type));
+ return -EACCES;
+ }
+
+ if (t == BPF_WRITE && rdonly_mem) {
+ verbose(env, "R%d cannot write into %s\n",
+ regno, reg_type_str(env, reg->type));
+ return -EACCES;
+ }
+
if (t == BPF_WRITE && value_regno >= 0 &&
is_pointer_value(env, value_regno)) {
verbose(env, "R%d leaks addr into mem\n", value_regno);
return -EACCES;
}
+
err = check_mem_region_access(env, regno, off, size,
reg->mem_size, false);
- if (!err && t == BPF_READ && value_regno >= 0)
+ if (!err && value_regno >= 0 && (t == BPF_READ || rdonly_mem))
mark_reg_unknown(env, regs, value_regno);
} else if (reg->type == PTR_TO_CTX) {
enum bpf_reg_type reg_type = SCALAR_VALUE;
@@ -6654,6 +6669,13 @@
regs[BPF_REG_0].type = PTR_TO_MEM | ret_flag;
regs[BPF_REG_0].mem_size = tsize;
} else {
+ /* MEM_RDONLY may be carried from ret_flag, but it
+ * doesn't apply on PTR_TO_BTF_ID. Fold it, otherwise
+ * it will confuse the check of PTR_TO_BTF_ID in
+ * check_mem_access().
+ */
+ ret_flag &= ~MEM_RDONLY;
+
regs[BPF_REG_0].type = PTR_TO_BTF_ID | ret_flag;
regs[BPF_REG_0].btf = meta.ret_btf;
regs[BPF_REG_0].btf_id = meta.ret_btf_id;
@@ -9455,7 +9477,7 @@
mark_reg_known_zero(env, regs, insn->dst_reg);
dst_reg->type = aux->btf_var.reg_type;
- switch (dst_reg->type) {
+ switch (base_type(dst_reg->type)) {
case PTR_TO_MEM:
dst_reg->mem_size = aux->btf_var.mem_size;
break;
@@ -11678,7 +11700,7 @@
err = -EINVAL;
goto err_put;
}
- aux->btf_var.reg_type = PTR_TO_MEM;
+ aux->btf_var.reg_type = PTR_TO_MEM | MEM_RDONLY;
aux->btf_var.mem_size = tsize;
} else {
aux->btf_var.reg_type = PTR_TO_BTF_ID;
