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bpf: Make per_cpu_ptr return rdonly PTR_TO_MEM.

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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: 63d9b80dcf ("bpf: Introducte bpf_this_cpu_ptr()")
Fixes: eaa6bcb71e ("bpf: Introduce bpf_per_cpu_ptr()")
Fixes: 4976b718c3 ("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
This commit is contained in:
Hao Luo 2021-12-16 16:31:50 -08:00 committed by Alexei Starovoitov
parent cf9f2f8d62
commit 34d3a78c68
2 changed files with 28 additions and 6 deletions
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4
kernel/bpf/helpers.c
View file

@ -682,7 +682,7 @@ BPF_CALL_2(bpf_per_cpu_ptr, const void *, ptr, u32, cpu)
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 @@ BPF_CALL_1(bpf_this_cpu_ptr, const void *, percpu_ptr)
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,
};

30
kernel/bpf/verifier.c
View file

@ -4399,15 +4399,30 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
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 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
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 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
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 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
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;