Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

[Minfei Huang]

2015-04-01 21:35 GMT+08:00 Jiri Kosina <jkosina@suse.cz>:
>
> On Wed, 1 Apr 2015, Minfei Huang wrote:
> >
> > Sorry, Use the gmail account to resend this patch, because the yahoo account cannt receive the maillist.
> >
> > ----
> >
> > As mentioned in the annotation, the patch module would not permit to
> > be removed once it is loaded.
> >
> > Kernel may crash in the case that the function in the patch module is
> > called during removing.
> >
> > We will increase the module reference when the patch module is enable,
> > so that the module cannt be removed. Once the module is disable, it will
> > be removed.
> >
> > Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
> > ---
> >  kernel/livepatch/core.c | 47 +++++++++++++++++++++++++++++++----------------
> >  1 file changed, 31 insertions(+), 16 deletions(-)
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 3f9f1d6..0266950 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
> >       return 0;
> >  }
> >
> > +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> > +{
> > +     int ret = 0;
> > +
> > +     ret = __klp_disable_patch(patch);
> > +     if (ret)
> > +             return ret;
> > +     module_put(patch->mod);
> > +     return ret;
> > +}
> > +
>
> Your patch doesn't solve the problem at all.
>
> There is no guarantee that once __klp_disable_patch() returns noone is
> using the old code any more.
>

Yes, thanks.

The __klp_disable_patch only guarantees that we will never call the
function in patch module. For now, patch module can never be removed
from the kernel once it was loaded. It may be inconvenience if we want
re-load a new patch module replace the old patch module.

Thanks
Minfei

> --
> Jiri Kosina
> SUSE Labs

Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

[Jiri Kosina]

On Wed, 1 Apr 2015, Minfei Huang wrote:

> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > > index 3f9f1d6..0266950 100644
> > > --- a/kernel/livepatch/core.c
> > > +++ b/kernel/livepatch/core.c
> > > @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
> > >       return 0;
> > >  }
> > >
> > > +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> > > +{
> > > +     int ret = 0;
> > > +
> > > +     ret = __klp_disable_patch(patch);
> > > +     if (ret)
> > > +             return ret;
> > > +     module_put(patch->mod);
> > > +     return ret;
> > > +}
> > > +
> >
> > Your patch doesn't solve the problem at all.
> >
> > There is no guarantee that once __klp_disable_patch() returns noone is
> > using the old code any more.
> >
> 
> Yes, thanks.
> 
> The __klp_disable_patch only guarantees that we will never call the
> function in patch module. For now, patch module can never be removed
> from the kernel once it was loaded. It may be inconvenience if we want
> re-load a new patch module replace the old patch module.

Patch stacking is possible though.

-- 
Jiri Kosina
SUSE Labs

Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

[Minfei Huang]

2015-04-01 22:13 GMT+08:00 Jiri Kosina <jkosina@suse.cz>:
> On Wed, 1 Apr 2015, Minfei Huang wrote:
>
>> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> > > index 3f9f1d6..0266950 100644
>> > > --- a/kernel/livepatch/core.c
>> > > +++ b/kernel/livepatch/core.c
>> > > @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
>> > >       return 0;
>> > >  }
>> > >
>> > > +static int __klp_disable_patch_nolock(struct klp_patch *patch)
>> > > +{
>> > > +     int ret = 0;
>> > > +
>> > > +     ret = __klp_disable_patch(patch);
>> > > +     if (ret)
>> > > +             return ret;
>> > > +     module_put(patch->mod);
>> > > +     return ret;
>> > > +}
>> > > +
>> >
>> > Your patch doesn't solve the problem at all.
>> >
>> > There is no guarantee that once __klp_disable_patch() returns noone is
>> > using the old code any more.
>> >
>>
>> Yes, thanks.
>>
>> The __klp_disable_patch only guarantees that we will never call the
>> function in patch module. For now, patch module can never be removed
>> from the kernel once it was loaded. It may be inconvenience if we want
>> re-load a new patch module replace the old patch module.
>
> Patch stacking is possible though.
>

How about check the stack when start to remove the patch module? We
can use the interface stop_machine to hang other CPU, then check and
remove if no function in patch module is used.

Thanks
Minfei

> --
> Jiri Kosina
> SUSE Labs

Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

[Josh Poimboeuf]

On Wed, Apr 01, 2015 at 10:40:19PM +0800, Minfei Huang wrote:
> 2015-04-01 22:13 GMT+08:00 Jiri Kosina <jkosina@suse.cz>:
> > On Wed, 1 Apr 2015, Minfei Huang wrote:
> >
> >> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> >> > > index 3f9f1d6..0266950 100644
> >> > > --- a/kernel/livepatch/core.c
> >> > > +++ b/kernel/livepatch/core.c
> >> > > @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
> >> > >       return 0;
> >> > >  }
> >> > >
> >> > > +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> >> > > +{
> >> > > +     int ret = 0;
> >> > > +
> >> > > +     ret = __klp_disable_patch(patch);
> >> > > +     if (ret)
> >> > > +             return ret;
> >> > > +     module_put(patch->mod);
> >> > > +     return ret;
> >> > > +}
> >> > > +
> >> >
> >> > Your patch doesn't solve the problem at all.
> >> >
> >> > There is no guarantee that once __klp_disable_patch() returns noone is
> >> > using the old code any more.
> >> >
> >>
> >> Yes, thanks.
> >>
> >> The __klp_disable_patch only guarantees that we will never call the
> >> function in patch module. For now, patch module can never be removed
> >> from the kernel once it was loaded. It may be inconvenience if we want
> >> re-load a new patch module replace the old patch module.
> >
> > Patch stacking is possible though.
> >
> 
> How about check the stack when start to remove the patch module? We
> can use the interface stop_machine to hang other CPU, then check and
> remove if no function in patch module is used.

Yeah, we'll eventually have something like that as part of the
consistency model.  The exact implementation is still undecided.  Until
then I think we want to disallow removing the patch module.

-- 
Josh

Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

[Jiri Kosina]

On Wed, 1 Apr 2015, Minfei Huang wrote:

> As mentioned in the annotation, the patch module would not permit to
> be removed once it is loaded.
> 
> Kernel may crash in the case that the function in the patch module is
> called during removing.
> 
> We will increase the module reference when the patch module is enable,
> so that the module cannt be removed. Once the module is disable, it will
> be removed.
> 
> Signed-off-by: Minfei Huang <minfei.huang@yahoo.com>
> ---
>  kernel/livepatch/core.c | 47 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 3f9f1d6..0266950 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
>  	return 0;
>  }
>  
> +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> +{
> +	int ret = 0;
> +
> +	ret = __klp_disable_patch(patch);
> +	if (ret)
> +		return ret;
> +	module_put(patch->mod);
> +	return ret;
> +}
> +

Your patch doesn't solve the problem at all.

There is no guarantee that once __klp_disable_patch() returns noone is 
using the old code any more.

-- 
Jiri Kosina
SUSE Labs