netdev - [PATCH bpf-next v2] bpf: reject kfunc calls that overflow insn->imm

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Message-ID: <20220208123348.40360-1-houtao1@huawei.com>
Date:   Tue, 8 Feb 2022 20:33:48 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <houtao1@...wei.com>
Subject: [PATCH bpf-next v2] bpf: reject kfunc calls that overflow insn->imm

Now kfunc call uses s32 to represent the offset between the address
of kfunc and __bpf_call_base, but it doesn't check whether or not
s32 will be overflowed, so add an extra checking to reject these
invalid kfunc calls.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
v2:
 * instead of checking the overflow in selftests, just reject
   these kfunc calls directly in verifier

v1: https://lore.kernel.org/bpf/20220206043107.18549-1-houtao1@huawei.com
---
 kernel/bpf/verifier.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a39eedecc93a..fd836e64b701 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1832,6 +1832,13 @@ static struct btf *find_kfunc_desc_btf(struct bpf_verifier_env *env,
 	return btf_vmlinux ?: ERR_PTR(-ENOENT);
 }
 
+static inline bool is_kfunc_call_imm_overflowed(unsigned long addr)
+{
+	unsigned long offset = BPF_CALL_IMM(addr);
+
+	return (unsigned long)(s32)offset != offset;
+}
+
 static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 {
 	const struct btf_type *func, *func_proto;
@@ -1925,6 +1932,12 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 		return -EINVAL;
 	}
 
+	if (is_kfunc_call_imm_overflowed(addr)) {
+		verbose(env, "address of kernel function %s is out of range\n",
+			func_name);
+		return -EINVAL;
+	}
+
 	desc = &tab->descs[tab->nr_descs++];
 	desc->func_id = func_id;
 	desc->imm = BPF_CALL_IMM(addr);
-- 
2.29.2