On 10/01/2015 12:29 PM, Ingo Molnar wrote:
>
> * Andrey Ryabinin <ryabinin....@gmail.com> wrote:
>
>> 2015-10-01 10:57 GMT+03:00 Ingo Molnar <mi...@kernel.org>:
>>> diff --git a/Documentation/filesystems/proc.txt
>>> b/Documentation/filesystems/proc.txt
>>> index d411ca63c8b6..db64f7d6492d 100644
>>> --- a/Documentation/filesystems/proc.txt
>>> +++ b/Documentation/filesystems/proc.txt
>>> @@ -140,7 +140,8 @@ Table 1-1: Process specific entries in /proc
>>> stat Process status
>>> statm Process memory status information
>>> status Process status in human readable form
>>> - wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
>>> + wchan If CONFIG_KALLSYMS=y, wchan (the kernel function the
>>> process is
>>> + blocked in) symbol string. "0" if not blocked or !KALLSYMS.
>>
>> /proc/PID/wchan is under #ifdef CONFIG_KALLSYMS.
>
> Yeah, indeed, so I clarified that text to now read:
>
> + wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
> + symbol the task is blocked in - or "0" if not blocked.
>
>>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>>> index b25eee4cead5..6f05aabce3aa 100644
>>> --- a/fs/proc/base.c
>>> +++ b/fs/proc/base.c
>>> @@ -430,13 +430,10 @@ static int proc_pid_wchan(struct seq_file *m, struct
>>> pid_namespace *ns,
>>>
>>> wchan = get_wchan(task);
>>>
>>> - if (lookup_symbol_name(wchan, symname) < 0) {
>>> - if (!ptrace_may_access(task, PTRACE_MODE_READ))
>>> - return 0;
>>> - seq_printf(m, "%lu", wchan);
>>> - } else {
>>> + if (!lookup_symbol_name(wchan, symname))
>>> seq_printf(m, "%s", symname);
>>> - }
>>> + else
>>> + seq_putc(m, '0');
>>
>> Maybe we should respect 'kptr_restrict' sysctl when we use '%ps', '%pB' etc.
>> printk formats (AFAIK %ps just prints address if KALLSYMS=n, or lookup
>> failed).
>> In that case you could just do 'seq_printf(m, "%ps", wchan)'.
>>
>> OTOH, %ps, %pS are used mostly in debugging, so investigating some crash in
>> production kernel with no !KALLSYMS and with kptr_restrict != 0 will be a
>> nightmare.
>
> So this code does not use %pX, it prints the symbol.
I think you misunderstood me.
Yes, this code currently doesn't use %pX, but it could:
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b25eee4..f58f66e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -425,18 +425,7 @@ static int proc_pid_auxv(struct seq_file *m, struct
pid_namespace *ns,
static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
- unsigned long wchan;
- char symname[KSYM_NAME_LEN];
-
- wchan = get_wchan(task);
-
- if (lookup_symbol_name(wchan, symname) < 0) {
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return 0;
- seq_printf(m, "%lu", wchan);
- } else {
- seq_printf(m, "%s", symname);
- }
+ seq_printf(m, "%ps", get_wchan(task));
return 0;
}
There is a problem here, though. %ps will print absolute kernel address instead
of symbol name
if KALLSYMS=n or if resolution of address failed.
So I was wondering, may be should just fix %ps ?
i.e. print 0 instead of absolute address if KALLSYMS=n or lookup failure?
> Yes, the symbol in itself is
> 'information' about the execution of the task in itself - but /proc per se is
> all
> about providing information about tasks in the system (including to
> unprivileged
> users), so there's IMHO little point in restricting this output any further
> ...
>
> I think ktrp_restrict is mostly about not exposing absolute addresses.
>
Right, and '%ps' may expose absolute address if KALLSYMS=n or address lookup
failed for some reason.
> Thanks,
>
> Ingo
>
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