On 05/14/2014 11:28 AM, Aravinda Prasad wrote:
> On Wednesday 30 April 2014 08:00 PM, Jiri Slaby wrote:
>> From: Jiri Kosina <jkos...@suse.cz>
>>
>> Provide initial implementation. We are now able to do ftrace-based
>> runtime patching of the kernel code.
>>
>> In addition to that, we will provide a kgr_patcher module in the next
>> patch to test the functionality.
>
> Hi Jiri,
>
> Interesting! I have couple of comments:
>
> I think with kgraft (also with kpatch, though have not looked into
> it yet), the patched function cannot be dynamically ftraced.
> Though dynamic ftrace can be enabled on the new code, the user is
> required to know the function label of the new code. This could
> potentially break existing scripts. I think this should be documented.
Hi,
of course that the functions can be traced. Look, I turned on tracing
for capable, then patched, then turned on tracing for new_capable (which
is the patched function). So now, trace shows:
console-kit-dae-535 [001] ...1 181.729698: capable <-vt_ioctl
console-kit-dae-539 [001] ...1 181.729741: capable <-vt_ioctl
console-kit-dae-541 [000] .N.1 181.906014: capable <-vt_ioctl
systemd-1 [001] ...1 181.937328: capable <-SyS_epoll_ctl
sshd-662 [001] ...1 246.437561: capable <-sock_setsockopt
sshd-662 [001] ...1 246.437564: new_capable
<-sock_setsockopt
sshd-662 [001] ...1 246.444790: capable <-sock_setsockopt
sshd-662 [001] ...1 246.444793: new_capable
<-sock_setsockopt
dbus-daemon-128 [000] .N.1 246.456307: capable <-SyS_epoll_ctl
dbus-daemon-128 [000] ...1 246.456611: new_capable <-SyS_epoll_ctl
There is no limitation thanks to the use of the ftrace subsystem. We are
just another user, i.e. another piece of code called in a loop for a
particular fentry location.
>> +/*
>> + * The stub needs to modify the RIP value stored in struct pt_regs
>> + * so that ftrace redirects the execution properly.
>> + */
>> +#define KGR_STUB_ARCH_SLOW(_name, _new_function) \
>> +static void _new_function ##_stub_slow (unsigned long ip, unsigned long
>> parent_ip, \
>> + struct ftrace_ops *ops, struct pt_regs *regs) \
>> +{ \
>> + struct kgr_loc_caches *c = ops->private; \
>> + \
>> + if (task_thread_info(current)->kgr_in_progress && current->mm) {\
>
> Is there a race here? The per task kgr_in_progress is set after
> the slow stub is registered in register_ftrace_function(). If the
> patched function is called in between it will be redirected to new code.
Hmm, that looks strange. I will look into that and the other comments
later (and comment separately). Thanks.
--
js
suse labs
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