Re: [PATCH 2/7] kprobes: Propagate error from arm_kprobe_ftrace()

Masami Hiramatsu
2015-02-27T07:35:47Z

(2015/02/27 1:13), Petr Mladek wrote:
> arm_kprobe_ftrace() could fail, especially after introducing ftrace IPMODIFY
> flag and LifePatching.
>
> registry_kprobe() and registry_aggr_kprobe() do not mind about the error
> because the kprobe gets disabled and they keep it registered.
>
> But enable_kprobe() should propagate the error because its tasks
> fails if ftrace fails.
>
> Also arm_all_kprobes() should return error if it happens. The behavior
> is a bit questionable here. This patch keeps the existing behavior and does
> the best effort. It tries to enable as many Kprobes as possible. It returns
> only the last error code if any. kprobes_all_disarmed is always cleared and
> the message about finished action is always printed. There is going to be
> a separate patch that will improve the behavior.

When I applied it on -tip/master, there is a hunk which is not cleanly applied.
Please rebase it on the latest tip/master, since some logic are changed.

Here I have some comments on it.

>
> Signed-off-by: Petr Mladek <pmladek@suse.cz>
> ---
> kernel/kprobes.c | 47 ++++++++++++++++++++++++++++++++---------------
> 1 file changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d1b9db690b9c..a69d23add983 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -929,7 +929,7 @@ static int prepare_kprobe(struct kprobe *p)
> }
>
> /* Caller must lock kprobe_mutex */
> -static void arm_kprobe_ftrace(struct kprobe *p)
> +static int arm_kprobe_ftrace(struct kprobe *p)
> {
> struct kprobe *kp;
> int ret;
> @@ -949,7 +949,7 @@ static void arm_kprobe_ftrace(struct kprobe *p)
> goto err_function;
> }
> kprobe_ftrace_enabled++;
> - return;
> + return ret;
>
> err_function:
> ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
> @@ -958,6 +958,7 @@ err_filter:
> if (kprobe_aggrprobe(p))
> list_for_each_entry_rcu(kp, &p->list, list)
> kp->flags |= KPROBE_FLAG_DISABLED;
> + return ret;
> }
>
> /* Caller must lock kprobe_mutex */
> @@ -976,17 +977,15 @@ static void disarm_kprobe_ftrace(struct kprobe *p)
> }
> #else /* !CONFIG_KPROBES_ON_FTRACE */
> #define prepare_kprobe(p) arch_prepare_kprobe(p)
> -#define arm_kprobe_ftrace(p) do {} while (0)
> +#define arm_kprobe_ftrace(p) (0)
> #define disarm_kprobe_ftrace(p) do {} while (0)
> #endif
>
> /* Arm a kprobe with text_mutex */
> -static void arm_kprobe(struct kprobe *kp)
> +static int arm_kprobe(struct kprobe *kp)
> {
> - if (unlikely(kprobe_ftrace(kp))) {
> - arm_kprobe_ftrace(kp);
> - return;
> - }
> + if (unlikely(kprobe_ftrace(kp)))
> + return arm_kprobe_ftrace(kp);
> /*
> * Here, since __arm_kprobe() doesn't use stop_machine(),
> * this doesn't cause deadlock on text_mutex. So, we don't
> @@ -995,6 +994,7 @@ static void arm_kprobe(struct kprobe *kp)
> mutex_lock(&text_mutex);
> __arm_kprobe(kp);
> mutex_unlock(&text_mutex);
> + return 0;
> }
>
> /* Disarm a kprobe with text_mutex */
> @@ -1332,10 +1332,15 @@ out:
> put_online_cpus();
> jump_label_unlock();
>
> + /* Arm when this is the first enabled kprobe at this address */
> if (ret == 0 && kprobe_disabled(ap) && !kprobe_disabled(p)) {
> ap->flags &= ~KPROBE_FLAG_DISABLED;
> if (!kprobes_all_disarmed)
> - /* Arm the breakpoint again. */
> + /*
> + * The kprobe is disabled and warning is printed
> + * on error. But we ignore the error code here
> + * because we keep it registered.
> + */

Why? if we can't arm it, we'd better make it fail.

> arm_kprobe(ap);
> }
> return ret;
> @@ -1540,6 +1545,11 @@ int register_kprobe(struct kprobe *p)
> &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
>
> if (!kprobes_all_disarmed && !kprobe_disabled(p))
> + /*
> + * The kprobe is disabled and warning is printed on error.
> + * But we ignore the error code here because we keep it
> + * registered.
> + */
> arm_kprobe(p);

Ditto. If we failed to enable it. We should make it fail and report an error
to caller.

Thank you,

>
> /* Try to optimize kprobe */
> @@ -2040,7 +2050,7 @@ int enable_kprobe(struct kprobe *kp)
>
> if (!kprobes_all_disarmed && kprobe_disabled(p)) {
> p->flags &= ~KPROBE_FLAG_DISABLED;
> - arm_kprobe(p);
> + ret = arm_kprobe(p);
> }
> out:
> mutex_unlock(&kprobe_mutex);
> @@ -2325,11 +2335,12 @@ static const struct file_operations debugfs_kprobe_blacklist_ops = {
> .release = seq_release,
> };
>
> -static void arm_all_kprobes(void)
> +static int arm_all_kprobes(void)
> {
> struct hlist_head *head;
> struct kprobe *p;
> unsigned int i;
> + int err, ret = 0;
>
> mutex_lock(&kprobe_mutex);
>
> @@ -2341,8 +2352,11 @@ static void arm_all_kprobes(void)
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> hlist_for_each_entry_rcu(p, head, hlist)
> - if (!kprobe_disabled(p))
> - arm_kprobe(p);
> + if (!kprobe_disabled(p)) {
> + err = arm_kprobe(p);
> + if (err)
> + ret = err;
> + }
> }
>
> kprobes_all_disarmed = false;
> @@ -2350,7 +2364,7 @@ static void arm_all_kprobes(void)
>
> already_enabled:
> mutex_unlock(&kprobe_mutex);
> - return;
> + return ret;
> }
>
> static void disarm_all_kprobes(void)
> @@ -2407,6 +2421,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
> {
> char buf[32];
> size_t buf_size;
> + int err = 0;
>
> buf_size = min(count, (sizeof(buf)-1));
> if (copy_from_user(buf, user_buf, buf_size))
> @@ -2417,7 +2432,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
> case 'y':
> case 'Y':
> case '1':
> - arm_all_kprobes();
> + err = arm_all_kprobes();
> break;
> case 'n':
> case 'N':
> @@ -2428,6 +2443,8 @@ static ssize_t write_enabled_file_bool(struct file *file,
> return -EINVAL;
> }
>
> + if (err)
> + return err;
> return count;
> }
>
>

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com