Add enforcement of expected types for context arguments tagged with
arg:ctx (__arg_ctx) tag.
First, any program type will accept generic `void *` context type when
combined with __arg_ctx tag.
Besides accepting "canonical" struct names and `void *`, for a bunch of
program types for which program context is actually a named struct, we
allows a bunch of pragmatic exceptions to match real-world and expected
usage:
- for kprobes, we always accept `struct pt_regs *`, as that's what
actually is passed as a context to any kprobe program;
- for perf_event, we resolve typedefs down to actual struct type and
accept `struct pt_regs *` if kernel's architecture actually defines
`bpf_user_pt_regs_t` as an alias for `struct pt_regs`; otherwise,
canonical `struct bpf_perf_event_data *` is expected and supported;
- for raw_tp/raw_tp.w programs, `u64/long *` are accepted, as that's
what's expected with BPF_PROG() usage; otherwise, canonical
`struct bpf_raw_tracepoint_args *` is expected;
- tp_btf supports both `struct bpf_raw_tracepoint_args *` and `u64 *`
formats, both are coded as expections as tp_btf is actually a TRACING
program type, which has no canonical context type;
- iterator programs accept `struct bpf_iter__xxx *` structs, currently
with no further iterator-type specific enforcement;
- fentry/fexit/fmod_ret/lsm/struct_ops all accept `u64 *`;
- classic tracepoint programs, as well as syscall and freplace
programs allow any user-provided type.
In all other cases kernel will enforce exact match of struct name to
expected canonical type. And if user-provided type doesn't match that
expectation, verifier will emit helpful message with expected type name.
Note a bit unnatural way the check is done after processing all the
arguments. This is done to avoid conflict between bpf and bpf-next
trees. Once trees converge, a small follow up patch will place a simple
btf_validate_prog_ctx_type() check into a proper ARG_PTR_TO_CTX branch
(which bpf-next tree patch refactored already), removing duplicated
arg:ctx detection logic.
Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
kernel/bpf/btf.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 129 insertions(+)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 10ac9efc662d..e64e38df08e6 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5709,6 +5709,118 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
return ctx_type;
}
+static int btf_validate_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
+ const struct btf_type *t, int arg,
+ enum bpf_prog_type prog_type,
+ enum bpf_attach_type attach_type)
+{
+ const struct btf_type *ctx_type;
+ const char *tname, *ctx_tname;
+
+ if (!btf_is_ptr(t)) {
+ bpf_log(log, "arg#%d type isn't a pointer\n", arg);
+ return -EINVAL;
+ }
+ t = btf_type_by_id(btf, t->type);
+ while (btf_type_is_modifier(t))
+ t = btf_type_by_id(btf, t->type);
+
+ /* `void *ctx __arg_ctx` is always valid */
+ if (btf_type_is_void(t))
+ return 0;
+
+ tname = btf_name_by_offset(btf, t->name_off);
+ if (str_is_empty(tname)) {
+ bpf_log(log, "arg#%d type doesn't have a name\n", arg);
+ return -EINVAL;
+ }
+
+ /* special cases */
+ switch (prog_type) {
+ case BPF_PROG_TYPE_KPROBE:
+ if (__btf_type_is_struct(t) && strcmp(tname, "pt_regs") == 0)
+ return 0;
+ break;
+ case BPF_PROG_TYPE_PERF_EVENT:
+ if (__builtin_types_compatible_p(bpf_user_pt_regs_t, struct pt_regs) &&
+ __btf_type_is_struct(t) && strcmp(tname, "pt_regs") == 0)
+ return 0;
+ break;
+ case BPF_PROG_TYPE_RAW_TRACEPOINT:
+ case BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE:
+ /* allow u64* as ctx */
+ if (btf_is_int(t) && t->size == 8)
+ return 0;
+ break;
+ case BPF_PROG_TYPE_TRACING:
+ switch (attach_type) {
+ case BPF_TRACE_RAW_TP:
+ /* tp_btf program is TRACING, so need special case here */
+ if (__btf_type_is_struct(t) &&
+ strcmp(tname, "bpf_raw_tracepoint_args") == 0)
+ return 0;
+ /* allow u64* as ctx */
+ if (btf_is_int(t) && t->size == 8)
+ return 0;
+ break;
+ case BPF_TRACE_ITER:
+ /* allow struct bpf_iter__xxx types only */
+ if (__btf_type_is_struct(t) &&
+ strncmp(tname, "bpf_iter__", sizeof("bpf_iter__") - 1) == 0)
+ return 0;
+ break;
+ case BPF_TRACE_FENTRY:
+ case BPF_TRACE_FEXIT:
+ case BPF_MODIFY_RETURN:
+ /* allow u64* as ctx */
+ if (btf_is_int(t) && t->size == 8)
+ return 0;
+ break;
+ default:
+ }
+ break;
+ case BPF_PROG_TYPE_LSM:
+ case BPF_PROG_TYPE_STRUCT_OPS:
+ /* allow u64* as ctx */
+ if (btf_is_int(t) && t->size == 8)
+ return 0;
+ break;
+ case BPF_PROG_TYPE_TRACEPOINT:
+ case BPF_PROG_TYPE_SYSCALL:
+ case BPF_PROG_TYPE_EXT:
+ return 0; /* anything goes */
+ default:
+ }
+
+ ctx_type = find_canonical_prog_ctx_type(prog_type);
+ if (!ctx_type) {
+ /* should not happen */
+ bpf_log(log, "btf_vmlinux is malformed\n");
+ return -EINVAL;
+ }
+
+ /* resolve typedefs and check that underlying structs are matching as well */
+ while (btf_type_is_modifier(ctx_type))
+ ctx_type = btf_type_by_id(btf_vmlinux, ctx_type->type);
+
+ /* if program type doesn't have distinctly named struct type for
+ * context, then __arg_ctx argument can only be `void *`, which we
+ * already checked above
+ */
+ if (!__btf_type_is_struct(ctx_type)) {
+ bpf_log(log, "arg#%d should be void pointer\n", arg);
+ return -EINVAL;
+ }
+
+ ctx_tname = btf_name_by_offset(btf_vmlinux, ctx_type->name_off);
+ if (!__btf_type_is_struct(t) || strcmp(ctx_tname, tname) != 0) {
+ bpf_log(log, "arg#%d should be `struct %s *`\n", arg, ctx_tname);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int btf_translate_to_vmlinux(struct bpf_verifier_log *log,
struct btf *btf,
const struct btf_type *t,
@@ -6953,6 +7065,23 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
return -EINVAL;
}
+ for (i = 0; i < nargs; i++) {
+ const char *tag;
+
+ if (sub->args[i].arg_type != ARG_PTR_TO_CTX)
+ continue;
+
+ /* check if arg has "arg:ctx" tag */
+ t = btf_type_by_id(btf, args[i].type);
+ tag = btf_find_decl_tag_value(btf, fn_t, i, "arg:");
+ if (IS_ERR_OR_NULL(tag) || strcmp(tag, "ctx") != 0)
+ continue;
+
+ if (btf_validate_prog_ctx_type(log, btf, t, i, prog_type,
+ prog->expected_attach_type))
+ return -EINVAL;
+ }
+
sub->arg_cnt = nargs;
sub->args_cached = true;
--
2.34.1
