bpf: Support __nullable argument suffix for tp_btf

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@kernel.org>
Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240911033719.91468-2-lulie@linux.alibaba.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 520f49f422fee232f728029e185b258183ac7c51..7e03a98ccb7cffaa1a9f7849f8951f0030481935 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6523,6 +6523,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
        if (prog_args_trusted(prog))
                info->reg_type |= PTR_TRUSTED;
 
+       if (btf_param_match_suffix(btf, &args[arg], "__nullable"))
+               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 d8520095ca030e1b578a5f3d329a4536e1183516..39d5710c68ad0a048b3f0f295560e931444aff56 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -28,6 +28,8 @@
 #include <linux/cpumask.h>
 #include <linux/bpf_mem_alloc.h>
 #include <net/xdp.h>
+#include <linux/trace_events.h>
+#include <linux/kallsyms.h>
 
 #include "disasm.h"
 
@@ -21154,11 +21156,13 @@ 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[KSYM_SYMBOL_LEN];
        const char prefix[] = "btf_trace_";
+       struct bpf_raw_event_map *btp;
        int ret = 0, subprog = -1, i;
        const struct btf_type *t;
        bool conservative = true;
-       const char *tname;
+       const char *tname, *fname;
        struct btf *btf;
        long addr = 0;
        struct module *mod = NULL;
@@ -21289,10 +21293,34 @@ 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.
+                */
+               btp = bpf_get_raw_tracepoint(tname);
+               if (!btp)
                        return -EINVAL;
+               fname = kallsyms_lookup((unsigned long)btp->bpf_func, NULL, NULL, NULL,
+                                       trace_symbol);
+               bpf_put_raw_tracepoint(btp);
+
+               if (fname)
+                       ret = btf_find_by_name_kind(btf, fname, BTF_KIND_FUNC);
+
+               if (!fname || ret < 0) {
+                       bpf_log(log, "Cannot find btf of tracepoint template, fall back to %s%s.\n",
+                               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 */