Re: [PATCH 1/3] perf-probe: Fix to check blacklist address correctly

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/3] perf-probe: Fix to check blacklist address correctly
Date: Wed, 6 May 2020 13:44:08 -0300	[thread overview]
Message-ID: <20200506164408.GA4323@kernel.org> (raw)
In-Reply-To: <158763966411.30755.5882376357738273695.stgit@devnote2>

Em Thu, Apr 23, 2020 at 08:01:04PM +0900, Masami Hiramatsu escreveu:
> Fix to check kprobe blacklist address correctly with
> relocated address by adjusting debuginfo address.
> 
> Since the address in the debuginfo is same as objdump,
> it is different from relocated kernel address with KASLR.
> Thus, the perf-probe always misses to catch the
> blacklisted addresses.

Thanks, applied, sorry for the delay,

- Arnaldo

> Without this patch, perf probe can not detect the blacklist
> addresses on KASLR enabled kernel.
> 
> =========
>   # perf probe kprobe_dispatcher
>   Failed to write event: Invalid argument
>     Error: Failed to add events.
> =========
> 
> With this patch, it correctly shows the error message.
> 
> =========
>   # perf probe kprobe_dispatcher
>   kprobe_dispatcher is blacklisted function, skip it.
>   Probe point 'kprobe_dispatcher' not found.
>     Error: Failed to add events.
> =========
> 
> Fixes: 9aaf5a5f479b ("perf probe: Check kprobes blacklist when adding new events")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: stable@vger.kernel.org
> ---
>  tools/perf/util/probe-event.c |   21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index eea132f512b0..f75df63309be 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -102,7 +102,7 @@ void exit_probe_symbol_maps(void)
>  	symbol__exit();
>  }
>  
> -static struct ref_reloc_sym *kernel_get_ref_reloc_sym(void)
> +static struct ref_reloc_sym *kernel_get_ref_reloc_sym(struct map **pmap)
>  {
>  	/* kmap->ref_reloc_sym should be set if host_machine is initialized */
>  	struct kmap *kmap;
> @@ -114,6 +114,10 @@ static struct ref_reloc_sym *kernel_get_ref_reloc_sym(void)
>  	kmap = map__kmap(map);
>  	if (!kmap)
>  		return NULL;
> +
> +	if (pmap)
> +		*pmap = map;
> +
>  	return kmap->ref_reloc_sym;
>  }
>  
> @@ -125,7 +129,7 @@ static int kernel_get_symbol_address_by_name(const char *name, u64 *addr,
>  	struct map *map;
>  
>  	/* ref_reloc_sym is just a label. Need a special fix*/
> -	reloc_sym = kernel_get_ref_reloc_sym();
> +	reloc_sym = kernel_get_ref_reloc_sym(NULL);
>  	if (reloc_sym && strcmp(name, reloc_sym->name) == 0)
>  		*addr = (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
>  	else {
> @@ -745,6 +749,7 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
>  				       int ntevs)
>  {
>  	struct ref_reloc_sym *reloc_sym;
> +	struct map *map;
>  	char *tmp;
>  	int i, skipped = 0;
>  
> @@ -753,7 +758,7 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
>  		return post_process_offline_probe_trace_events(tevs, ntevs,
>  						symbol_conf.vmlinux_name);
>  
> -	reloc_sym = kernel_get_ref_reloc_sym();
> +	reloc_sym = kernel_get_ref_reloc_sym(&map);
>  	if (!reloc_sym) {
>  		pr_warning("Relocated base symbol is not found!\n");
>  		return -EINVAL;
> @@ -764,9 +769,13 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
>  			continue;
>  		if (tevs[i].point.retprobe && !kretprobe_offset_is_supported())
>  			continue;
> -		/* If we found a wrong one, mark it by NULL symbol */
> +		/*
> +		 * If we found a wrong one, mark it by NULL symbol.
> +		 * Since addresses in debuginfo is same as objdump, we need
> +		 * to convert it to addresses on memory.
> +		 */
>  		if (kprobe_warn_out_range(tevs[i].point.symbol,
> -					  tevs[i].point.address)) {
> +			map__objdump_2mem(map, tevs[i].point.address))) {
>  			tmp = NULL;
>  			skipped++;
>  		} else {
> @@ -2936,7 +2945,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>  	/* Note that the symbols in the kmodule are not relocated */
>  	if (!pev->uprobes && !pev->target &&
>  			(!pp->retprobe || kretprobe_offset_is_supported())) {
> -		reloc_sym = kernel_get_ref_reloc_sym();
> +		reloc_sym = kernel_get_ref_reloc_sym(NULL);
>  		if (!reloc_sym) {
>  			pr_warning("Relocated base symbol is not found!\n");
>  			ret = -EINVAL;
> 

-- 

- Arnaldo