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Message-ID: <1868732.tdWV9SEqCh@pwmachine>
Date: Tue, 31 Oct 2023 23:24:43 +0200
From: Francis Laniel <flaniel@...ux.microsoft.com>
To: LKML <linux-kernel@...r.kernel.org>,
Linux trace kernel <linux-trace-kernel@...r.kernel.org>,
"Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH for-next] tracing/kprobes: Add symbol counting check when module loads
Hi!
Le dimanche 29 octobre 2023, 05:10:46 EET Masami Hiramatsu (Google) a écrit :
> From: Masami Hiramatsu (Google) <mhiramat@...nel.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.
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.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(struct
> notifier_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",
> 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.
> 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.
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