Re: [PATCH v2 bpf-next 0/5] ftrace: host klp and bpf trampoline together

Re: [PATCH v2 bpf-next 0/5] ftrace: host klp and bpf trampoline together

[Steven Rostedt]

I just realized that none of the live kernel patching folks are Cc'd on
this thread. I think they will care much more about this than I do.

-- Steve


On Thu, 2 Jun 2022 12:37:01 -0700
Song Liu <song@kernel.org> wrote:

> Changes v1 => v2:
> 1. Fix build errors for different config. (kernel test robot)
> 
> Kernel Live Patch (livepatch, or klp) and bpf trampoline are important
> features for modern systems. This set allows the two to work on the same
> kernel function as the same time.
> 
> live patch uses ftrace with IPMODIFY, while bpf trampoline use direct
> ftrace. Existing policy does not allow the two to attach to the same kernel
> function. This is changed by fine tuning ftrace IPMODIFY policy, and allows
> one non-DIRECT IPMODIFY ftrace_ops and one non-IPMODIFY DIRECT ftrace_ops
> on the same kernel function at the same time. Please see 3/5 for more
> details on this.
> 
> Note that, one of the constraint here is to let bpf trampoline use direct
> call when it is not working on the same function as live patch. This is
> achieved by allowing ftrace code to ask bpf trampoline to make changes.
> 
> Jiri Olsa (1):
>   bpf, x64: Allow to use caller address from stack
> 
> Song Liu (4):
>   ftrace: allow customized flags for ftrace_direct_multi ftrace_ops
>   ftrace: add modify_ftrace_direct_multi_nolock
>   ftrace: introduce FTRACE_OPS_FL_SHARE_IPMODIFY
>   bpf: trampoline: support FTRACE_OPS_FL_SHARE_IPMODIFY
> 
>  arch/x86/net/bpf_jit_comp.c |  13 +-
>  include/linux/bpf.h         |   8 ++
>  include/linux/ftrace.h      |  79 +++++++++++
>  kernel/bpf/trampoline.c     | 109 +++++++++++++--
>  kernel/trace/ftrace.c       | 269 +++++++++++++++++++++++++++++++-----
>  5 files changed, 424 insertions(+), 54 deletions(-)
> 
> --
> 2.30.2

Re: [PATCH v2 bpf-next 0/5] ftrace: host klp and bpf trampoline together

[Song Liu]

> On Jul 11, 2022, at 4:55 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> I just realized that none of the live kernel patching folks are Cc'd on
> this thread. I think they will care much more about this than I do.

vger.kernel.org often drops my email when the CC list is too long. So I
try to keep the list short. In this case, since we are not changing live
patch code, and there isn't any negative impact for live patch side, I 
didn't CC live patch folks. 

I will at least CC live-patching@ in the next version. 

Thanks,
Song

PS: I am the live patch guy at Meta. :)


> 
> -- Steve
> 
> 
> On Thu, 2 Jun 2022 12:37:01 -0700
> Song Liu <song@kernel.org> wrote:
> 
>> Changes v1 => v2:
>> 1. Fix build errors for different config. (kernel test robot)
>> 
>> Kernel Live Patch (livepatch, or klp) and bpf trampoline are important
>> features for modern systems. This set allows the two to work on the same
>> kernel function as the same time.
>> 
>> live patch uses ftrace with IPMODIFY, while bpf trampoline use direct
>> ftrace. Existing policy does not allow the two to attach to the same kernel
>> function. This is changed by fine tuning ftrace IPMODIFY policy, and allows
>> one non-DIRECT IPMODIFY ftrace_ops and one non-IPMODIFY DIRECT ftrace_ops
>> on the same kernel function at the same time. Please see 3/5 for more
>> details on this.
>> 
>> Note that, one of the constraint here is to let bpf trampoline use direct
>> call when it is not working on the same function as live patch. This is
>> achieved by allowing ftrace code to ask bpf trampoline to make changes.
>> 
>> Jiri Olsa (1):
>>  bpf, x64: Allow to use caller address from stack
>> 
>> Song Liu (4):
>>  ftrace: allow customized flags for ftrace_direct_multi ftrace_ops
>>  ftrace: add modify_ftrace_direct_multi_nolock
>>  ftrace: introduce FTRACE_OPS_FL_SHARE_IPMODIFY
>>  bpf: trampoline: support FTRACE_OPS_FL_SHARE_IPMODIFY
>> 
>> arch/x86/net/bpf_jit_comp.c |  13 +-
>> include/linux/bpf.h         |   8 ++
>> include/linux/ftrace.h      |  79 +++++++++++
>> kernel/bpf/trampoline.c     | 109 +++++++++++++--
>> kernel/trace/ftrace.c       | 269 +++++++++++++++++++++++++++++++-----
>> 5 files changed, 424 insertions(+), 54 deletions(-)
>> 
>> --
>> 2.30.2
> 

Re: [PATCH v2 bpf-next 0/5] ftrace: host klp and bpf trampoline together

[Steven Rostedt]

On Tue, 12 Jul 2022 05:15:26 +0000
Song Liu <songliubraving@fb.com> wrote:

> > On Jul 11, 2022, at 4:55 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > I just realized that none of the live kernel patching folks are Cc'd on
> > this thread. I think they will care much more about this than I do.  
> 
> vger.kernel.org often drops my email when the CC list is too long. So I

Oh, they fixed that. I've had over 20 Cc's and it still works. ;-)

> try to keep the list short. In this case, since we are not changing live
> patch code, and there isn't any negative impact for live patch side, I 
> didn't CC live patch folks. 

It affects them indirectly, and they should be aware of what is happening
underneath.

> 
> I will at least CC live-patching@ in the next version. 

Thanks.

-- Steve