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authorDaniel Borkmann <daniel@iogearbox.net>2017-07-02 02:13:27 +0200
committerDavid S. Miller <davem@davemloft.net>2017-07-03 02:22:52 -0700
commitf96da09473b52c09125cc9bf7d7d4576ae8229e0 (patch)
tree5a246cb2a6522950dff8e3a3d4c223e225c99a01 /include/linux/bpf.h
parent2be7e212d5419a400d051c84ca9fdd083e5aacac (diff)
bpf: simplify narrower ctx access
This work tries to make the semantics and code around the narrower ctx access a bit easier to follow. Right now everything is done inside the .is_valid_access(). Offset matching is done differently for read/write types, meaning writes don't support narrower access and thus matching only on offsetof(struct foo, bar) is enough whereas for read case that supports narrower access we must check for offsetof(struct foo, bar) + offsetof(struct foo, bar) + sizeof(<bar>) - 1 for each of the cases. For read cases of individual members that don't support narrower access (like packet pointers or skb->cb[] case which has its own narrow access logic), we check as usual only offsetof(struct foo, bar) like in write case. Then, for the case where narrower access is allowed, we also need to set the aux info for the access. Meaning, ctx_field_size and converted_op_size have to be set. First is the original field size e.g. sizeof(<bar>) as in above example from the user facing ctx, and latter one is the target size after actual rewrite happened, thus for the kernel facing ctx. Also here we need the range match and we need to keep track changing convert_ctx_access() and converted_op_size from is_valid_access() as both are not at the same location. We can simplify the code a bit: check_ctx_access() becomes simpler in that we only store ctx_field_size as a meta data and later in convert_ctx_accesses() we fetch the target_size right from the location where we do convert. Should the verifier be misconfigured we do reject for BPF_WRITE cases or target_size that are not provided. For the subsystems, we always work on ranges in is_valid_access() and add small helpers for ranges and narrow access, convert_ctx_accesses() sets target_size for the relevant instruction. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: John Fastabend <john.fastabend@gmail.com> Cc: Yonghong Song <yhs@fb.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/bpf.h')
-rw-r--r--include/linux/bpf.h9
1 files changed, 7 insertions, 2 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5175729270d7..b69e7a5869ff 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -156,9 +156,14 @@ struct bpf_prog;
struct bpf_insn_access_aux {
enum bpf_reg_type reg_type;
int ctx_field_size;
- int converted_op_size;
};
+static inline void
+bpf_ctx_record_field_size(struct bpf_insn_access_aux *aux, u32 size)
+{
+ aux->ctx_field_size = size;
+}
+
struct bpf_verifier_ops {
/* return eBPF function prototype for verification */
const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id);
@@ -173,7 +178,7 @@ struct bpf_verifier_ops {
u32 (*convert_ctx_access)(enum bpf_access_type type,
const struct bpf_insn *src,
struct bpf_insn *dst,
- struct bpf_prog *prog);
+ struct bpf_prog *prog, u32 *target_size);
int (*test_run)(struct bpf_prog *prog, const union bpf_attr *kattr,
union bpf_attr __user *uattr);
};