From: Hao Luo <haoluo@google.com>
To: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Cc: Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
bpf@vger.kernel.org, Hao Luo <haoluo@google.com>
Subject: [PATCH bpf-next v2 7/9] bpf: Make per_cpu_ptr return rdonly PTR_TO_MEM.
Date: Thu, 16 Dec 2021 16:31:50 -0800 [thread overview]
Message-ID: <20211217003152.48334-8-haoluo@google.com> (raw)
In-Reply-To: <20211217003152.48334-1-haoluo@google.com>
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>
---
kernel/bpf/helpers.c | 4 ++--
kernel/bpf/verifier.c | 30 ++++++++++++++++++++++++++----
2 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index c49dc5cbe0a7..6a65e2a62b01 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -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,
};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 543e729fa3cc..b9453413d1d8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4334,15 +4334,30 @@ 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 rdonly %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;
@@ -6589,6 +6604,13 @@ 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;
@@ -9390,7 +9412,7 @@ 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;
@@ -11610,7 +11632,7 @@ 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;
--
2.34.1.173.g76aa8bc2d0-goog
next prev parent reply other threads:[~2021-12-17 0:32 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 0:31 [PATCH bpf-next v2 0/9] Introduce composable bpf types Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 1/9] bpf: Introduce composable reg, ret and arg types Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 2/9] bpf: Replace ARG_XXX_OR_NULL with ARG_XXX | PTR_MAYBE_NULL Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 3/9] bpf: Replace RET_XXX_OR_NULL with RET_XXX " Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 4/9] bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX " Hao Luo
2021-12-18 21:48 ` Alexei Starovoitov
2021-12-17 0:31 ` [PATCH bpf-next v2 5/9] bpf: Introduce MEM_RDONLY flag Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 6/9] bpf: Convert PTR_TO_MEM_OR_NULL to composable types Hao Luo
2021-12-17 0:31 ` Hao Luo [this message]
2021-12-18 21:48 ` [PATCH bpf-next v2 7/9] bpf: Make per_cpu_ptr return rdonly PTR_TO_MEM Alexei Starovoitov
2021-12-17 0:31 ` [PATCH bpf-next v2 8/9] bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem Hao Luo
2021-12-18 21:48 ` Alexei Starovoitov
2021-12-20 20:14 ` Hao Luo
2021-12-17 0:31 ` [PATCH bpf-next v2 9/9] bpf/selftests: Test PTR_TO_RDONLY_MEM Hao Luo
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