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 <[email protected]> Signed-off-by: Philo Lu <[email protected]> --- 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
