Pointers passed to tp_btf were trusted to be valid, but some tracepoints
do take NULL pointer as input, such as trace_tcp_send_reset(). Then the
invalid memory access cannot be detected by verifier.
This patch fix it by add a suffix "__nullable" to the unreliable
argument. The suffix is shown in btf, and PTR_MAYBE_NULL will be added
to nullable arguments. Then users must check the pointer before use it.
A problem here is that we use "btf_trace_##call" to search func_proto.
As it is a typedef, argument names as well as the suffix are not
recorded. To solve this, I use bpf_raw_event_map to find
"__bpf_trace##template" from "btf_trace_##call", and then we can see the
suffix.
Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Philo Lu <lulie@xxxxxxxxxxxxxxxxx>
---
kernel/bpf/btf.c | 13 +++++++++++++
kernel/bpf/verifier.c | 36 +++++++++++++++++++++++++++++++++---
2 files changed, 46 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1e29281653c62..157f5e1247c81 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6385,6 +6385,16 @@ static bool prog_args_trusted(const struct bpf_prog *prog)
}
}
+static bool prog_arg_maybe_null(const struct bpf_prog *prog, const struct btf *btf,
+ const struct btf_param *arg)
+{
+ if (prog->type != BPF_PROG_TYPE_TRACING ||
+ prog->expected_attach_type != BPF_TRACE_RAW_TP)
+ return false;
+
+ return btf_param_match_suffix(btf, arg, "__nullable");
+}
+
int btf_ctx_arg_offset(const struct btf *btf, const struct btf_type *func_proto,
u32 arg_no)
{
@@ -6554,6 +6564,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
if (prog_args_trusted(prog))
info->reg_type |= PTR_TRUSTED;
+ if (prog_arg_maybe_null(prog, btf, &args[arg]))
+ info->reg_type |= PTR_MAYBE_NULL;
+
if (tgt_prog) {
enum bpf_prog_type tgt_type;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 217eb0eafa2a6..9ee68ed915dfe 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -28,6 +28,7 @@
#include <linux/cpumask.h>
#include <linux/bpf_mem_alloc.h>
#include <net/xdp.h>
+#include <linux/trace_events.h>
#include "disasm.h"
@@ -21780,6 +21781,8 @@ static int check_non_sleepable_error_inject(u32 btf_id)
return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
}
+#define BTF_MAX_NAME_SIZE 128
+
int bpf_check_attach_target(struct bpf_verifier_log *log,
const struct bpf_prog *prog,
const struct bpf_prog *tgt_prog,
@@ -21788,6 +21791,8 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
{
bool prog_extension = prog->type == BPF_PROG_TYPE_EXT;
bool prog_tracing = prog->type == BPF_PROG_TYPE_TRACING;
+ char trace_symbol[BTF_MAX_NAME_SIZE];
+ const struct bpf_raw_event_map *btp;
const char prefix[] = "btf_trace_";
int ret = 0, subprog = -1, i;
const struct btf_type *t;
@@ -21795,6 +21800,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
const char *tname;
struct btf *btf;
long addr = 0;
+ char *fname;
struct module *mod = NULL;
if (!btf_id) {
@@ -21923,10 +21929,34 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
return -EINVAL;
}
tname += sizeof(prefix) - 1;
- t = btf_type_by_id(btf, t->type);
- if (!btf_type_is_ptr(t))
- /* should never happen in valid vmlinux build */
+
+ /* The func_proto of "btf_trace_##tname" is generated from typedef without argument
+ * names. Thus using bpf_raw_event_map to get argument names. For module, the module
+ * name is printed in "%ps" after the template function name, so use strsep to cut
+ * it off.
+ */
+ btp = bpf_get_raw_tracepoint(tname);
+ if (!btp)
return -EINVAL;
+ sprintf(trace_symbol, "%ps", btp->bpf_func);
+ fname = trace_symbol;
+ fname = strsep(&fname, " ");
+
+ ret = btf_find_by_name_kind(btf, fname, BTF_KIND_FUNC);
+ if (ret < 0) {
+ bpf_log(log, "Cannot find btf of template %s, fall back to %s%s.\n",
+ fname, prefix, tname);
+ t = btf_type_by_id(btf, t->type);
+ if (!btf_type_is_ptr(t))
+ /* should never happen in valid vmlinux build */
+ return -EINVAL;
+ } else {
+ t = btf_type_by_id(btf, ret);
+ if (!btf_type_is_func(t))
+ /* should never happen in valid vmlinux build */
+ return -EINVAL;
+ }
+
t = btf_type_by_id(btf, t->type);
if (!btf_type_is_func_proto(t))
/* should never happen in valid vmlinux build */
--
2.32.0.3.g01195cf9f
