From c6f1bfe89ac95dc829dcb4ed54780da134ac5fce Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Thu, 27 Jan 2022 07:46:06 -0800 Subject: bpf: reject program if a __user tagged memory accessed in kernel way BPF verifier supports direct memory access for BPF_PROG_TYPE_TRACING type of bpf programs, e.g., a->b. If "a" is a pointer pointing to kernel memory, bpf verifier will allow user to write code in C like a->b and the verifier will translate it to a kernel load properly. If "a" is a pointer to user memory, it is expected that bpf developer should be bpf_probe_read_user() helper to get the value a->b. Without utilizing BTF __user tagging information, current verifier will assume that a->b is a kernel memory access and this may generate incorrect result. Now BTF contains __user information, it can check whether the pointer points to a user memory or not. If it is, the verifier can reject the program and force users to use bpf_probe_read_user() helper explicitly. In the future, we can easily extend btf_add_space for other address space tagging, for example, rcu/percpu etc. Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20220127154606.654961-1-yhs@fb.com Signed-off-by: Alexei Starovoitov --- include/linux/btf.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux/btf.h') diff --git a/include/linux/btf.h b/include/linux/btf.h index b12cfe3b12bb..f6c43dd513fa 100644 --- a/include/linux/btf.h +++ b/include/linux/btf.h @@ -238,6 +238,11 @@ static inline bool btf_type_is_var(const struct btf_type *t) return BTF_INFO_KIND(t->info) == BTF_KIND_VAR; } +static inline bool btf_type_is_type_tag(const struct btf_type *t) +{ + return BTF_INFO_KIND(t->info) == BTF_KIND_TYPE_TAG; +} + /* union is only a special case of struct: * all its offsetof(member) == 0 */ -- cgit v1.2.3-71-gd317