bpf: Check attach type at prog load time

== The problem ==

There are use-cases when a program of some type can be attached to
multiple attach points and those attach points must have different
permissions to access context or to call helpers.

E.g. context structure may have fields for both IPv4 and IPv6 but it
doesn't make sense to read from / write to IPv6 field when attach point
is somewhere in IPv4 stack.

Same applies to BPF-helpers: it may make sense to call some helper from
some attach point, but not from other for same prog type.

== The solution ==

Introduce `expected_attach_type` field in in `struct bpf_attr` for
`BPF_PROG_LOAD` command. If scenario described in "The problem" section
is the case for some prog type, the field will be checked twice:

1) At load time prog type is checked to see if attach type for it must
   be known to validate program permissions correctly. Prog will be
   rejected with EINVAL if it's the case and `expected_attach_type` is
   not specified or has invalid value.

2) At attach time `attach_type` is compared with `expected_attach_type`,
   if prog type requires to have one, and, if they differ, attach will
   be rejected with EINVAL.

The `expected_attach_type` is now available as part of `struct bpf_prog`
in both `bpf_verifier_ops->is_valid_access()` and
`bpf_verifier_ops->get_func_proto()` () and can be used to check context
accesses and calls to helpers correspondingly.

Initially the idea was discussed by Alexei Starovoitov <ast@fb.com> and
Daniel Borkmann <daniel@iogearbox.net> here:
https://marc.info/?l=linux-netdev&m=152107378717201&w=2

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 18 insertions, 9 deletions

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 463e72d18c4c..d88e96d4e12c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -524,7 +524,8 @@ static const struct bpf_func_proto bpf_probe_read_str_proto = {
         .arg3_type      = ARG_ANYTHING,
 };
 
-static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
         switch (func_id) {
         case BPF_FUNC_map_lookup_elem:
@@ -568,7 +569,8 @@ static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
         }
 }
 
-static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
         switch (func_id) {
         case BPF_FUNC_perf_event_output:
@@ -582,12 +584,13 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
                 return &bpf_override_return_proto;
 #endif
         default:
-                return tracing_func_proto(func_id);
+                return tracing_func_proto(func_id, prog);
         }
 }
 
 /* bpf+kprobe programs can access fields of 'struct pt_regs' */
 static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
+                                        const struct bpf_prog *prog,
                                         struct bpf_insn_access_aux *info)
 {
         if (off < 0 || off >= sizeof(struct pt_regs))
@@ -661,7 +664,8 @@ static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
         .arg3_type      = ARG_ANYTHING,
 };
 
-static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
         switch (func_id) {
         case BPF_FUNC_perf_event_output:
@@ -669,11 +673,12 @@ static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
         case BPF_FUNC_get_stackid:
                 return &bpf_get_stackid_proto_tp;
         default:
-                return tracing_func_proto(func_id);
+                return tracing_func_proto(func_id, prog);
         }
 }
 
 static bool tp_prog_is_valid_access(int off, int size, enum bpf_access_type type,
+                                    const struct bpf_prog *prog,
                                     struct bpf_insn_access_aux *info)
 {
         if (off < sizeof(void *) || off >= PERF_MAX_TRACE_SIZE)
@@ -721,7 +726,8 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto = {
          .arg3_type      = ARG_CONST_SIZE,
 };
 
-static const struct bpf_func_proto *pe_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
         switch (func_id) {
         case BPF_FUNC_perf_event_output:
@@ -731,7 +737,7 @@ static const struct bpf_func_proto *pe_prog_func_proto(enum bpf_func_id func_id)
         case BPF_FUNC_perf_prog_read_value:
                 return &bpf_perf_prog_read_value_proto;
         default:
-                return tracing_func_proto(func_id);
+                return tracing_func_proto(func_id, prog);
         }
 }
 
@@ -781,7 +787,8 @@ static const struct bpf_func_proto bpf_get_stackid_proto_raw_tp = {
         .arg3_type      = ARG_ANYTHING,
 };
 
-static const struct bpf_func_proto *raw_tp_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
         switch (func_id) {
         case BPF_FUNC_perf_event_output:
@@ -789,12 +796,13 @@ static const struct bpf_func_proto *raw_tp_prog_func_proto(enum bpf_func_id func
         case BPF_FUNC_get_stackid:
                 return &bpf_get_stackid_proto_raw_tp;
         default:
-                return tracing_func_proto(func_id);
+                return tracing_func_proto(func_id, prog);
         }
 }
 
 static bool raw_tp_prog_is_valid_access(int off, int size,
                                         enum bpf_access_type type,
+                                        const struct bpf_prog *prog,
                                         struct bpf_insn_access_aux *info)
 {
         /* largest tracepoint in the kernel has 12 args */
@@ -816,6 +824,7 @@ const struct bpf_prog_ops raw_tracepoint_prog_ops = {
 };
 
 static bool pe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
+                                    const struct bpf_prog *prog,
                                     struct bpf_insn_access_aux *info)
 {
         const int size_u64 = sizeof(u64);