Re: [PATCH for-next] tracing/kprobes: Add symbol counting check when module loads
From: Francis Laniel <hidden>
Date: 2023-10-31 21:24:51
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Hi! Le dimanche 29 octobre 2023, 05:10:46 EET Masami Hiramatsu (Google) a écrit :
From: Masami Hiramatsu (Google) <mhiramat@kernel.org> Check the number of probe target symbols in the target module when the module is loaded. If the probe is not on the unique name symbols in the module, it will be rejected at that point. Note that the symbol which has a unique name in the target module, it will be accepted even if there are same-name symbols in the kernel or other modules,
I am wondering about symbols which are only part of one specific module. I wrote a comment about it below, please let me know what you think about it.
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Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> --- kernel/trace/trace_kprobe.c | 112 ++++++++++++++++++++++++++----------------- 1 file changed, 68 insertions(+), 44 deletions(-)diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c index e834f149695b..90cf2219adb4 100644 --- a/kernel/trace/trace_kprobe.c +++ b/kernel/trace/trace_kprobe.c@@ -670,6 +670,21 @@ static int register_trace_kprobe(struct trace_kprobe*tk) return ret; } +static int validate_module_probe_symbol(const char *modname, const char *symbol); + +static int register_module_trace_kprobe(struct module *mod, struct trace_kprobe *tk) +{ + const char *p; + int ret = 0; + + p = strchr(trace_kprobe_symbol(tk), ':'); + if (p) + ret = validate_module_probe_symbol(module_name(mod), p++); + if (!ret) + ret = register_trace_kprobe(tk); + return ret; +} + /* Module notifier call back, checking event on the module */ static int trace_kprobe_module_callback(struct notifier_block *nb, unsigned long val, void *data)@@ -688,7 +703,7 @@ static int trace_kprobe_module_callback(structnotifier_block *nb, if (trace_kprobe_within_module(tk, mod)) { /* Don't need to check busy - this should have gone. */ __unregister_trace_kprobe(tk); - ret = __register_trace_kprobe(tk); + ret = register_module_trace_kprobe(mod, tk); if (ret) pr_warn("Failed to re-register probe %s on %s:
%d\n",
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trace_probe_name(&tk->tp),@@ -729,17 +744,55 @@ static int count_mod_symbols(void *data, const char*name, unsigned long unused) return 0; } -static unsigned int number_of_same_symbols(char *func_name) +static unsigned int number_of_same_symbols(const char *mod, const char *func_name) { struct sym_count_ctx ctx = { .count = 0, .name = func_name }; - kallsyms_on_each_match_symbol(count_symbols, func_name, &ctx.count); + if (!mod) + kallsyms_on_each_match_symbol(count_symbols, func_name,
&ctx.count);
- module_kallsyms_on_each_symbol(NULL, count_mod_symbols, &ctx); + module_kallsyms_on_each_symbol(mod, count_mod_symbols, &ctx);
I may be missing something here or reviewing too quickly. Wouldn't this function return count to be 0 if func_name is only part of the module named mod? Indeed, if the function is not in kernel symbol, kallsyms_on_each_match_symbol() will not loop. And, by giving mod to module_kallsyms_on_each_symbol(), the corresponding module will be skipped, so count_mob_symbols() would not be called. Hence, we would have 0 as count, which would lead to ENOENT later.
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return ctx.count; } +static int validate_module_probe_symbol(const char *modname, const char *symbol) +{ + unsigned int count = number_of_same_symbols(modname, symbol); + + if (count > 1) { + /* + * Users should use ADDR to remove the ambiguity of + * using KSYM only. + */ + return -EADDRNOTAVAIL; + } else if (count == 0) { + /* + * We can return ENOENT earlier than when register the + * kprobe. + */ + return -ENOENT; + } + return 0; +} + +static int validate_probe_symbol(char *symbol) +{ + char *mod = NULL, *p; + int ret; + + p = strchr(symbol, ':'); + if (p) { + mod = symbol; + symbol = p + 1; + *p = '\0'; + } + ret = validate_module_probe_symbol(mod, symbol); + if (p) + *p = ':'; + return ret; +} + static int __trace_kprobe_create(int argc, const char *argv[]) { /*@@ -859,6 +912,14 @@ static int __trace_kprobe_create(int argc, const char*argv[]) trace_probe_log_err(0, BAD_PROBE_ADDR); goto parse_error; } + ret = validate_probe_symbol(symbol); + if (ret) { + if (ret == -EADDRNOTAVAIL) + trace_probe_log_err(0, NON_UNIQ_SYMBOL); + else + trace_probe_log_err(0, BAD_PROBE_ADDR); + goto parse_error; + } if (is_return) ctx.flags |= TPARG_FL_RETURN; ret = kprobe_on_func_entry(NULL, symbol, offset);@@ -871,31 +932,6 @@ static int __trace_kprobe_create(int argc, const char*argv[]) } } - if (symbol && !strchr(symbol, ':')) { - unsigned int count; - - count = number_of_same_symbols(symbol); - if (count > 1) { - /* - * Users should use ADDR to remove the ambiguity of - * using KSYM only. - */ - trace_probe_log_err(0, NON_UNIQ_SYMBOL); - ret = -EADDRNOTAVAIL; - - goto error; - } else if (count == 0) { - /* - * We can return ENOENT earlier than when register the - * kprobe. - */ - trace_probe_log_err(0, BAD_PROBE_ADDR); - ret = -ENOENT; - - goto error; - } - } - trace_probe_log_set_index(0); if (event) { ret = traceprobe_parse_event_name(&event, &group, gbuf,@@ -1767,21 +1803,9 @@ create_local_trace_kprobe(char *func, void *addr,unsigned long offs, char *event; if (func) { - unsigned int count; - - count = number_of_same_symbols(func); - if (count > 1) - /* - * Users should use addr to remove the ambiguity of - * using func only. - */ - return ERR_PTR(-EADDRNOTAVAIL); - else if (count == 0) - /* - * We can return ENOENT earlier than when register the - * kprobe. - */ - return ERR_PTR(-ENOENT); + ret = validate_probe_symbol(func); + if (ret) + return ERR_PTR(ret); } /*
Best regards.