linux-kernel - [PATCH v4 bpf-next 0/4] ftrace: host klp and bpf trampoline together

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Date:   Sun, 17 Jul 2022 22:54:45 -0700
From:   Song Liu <song@...nel.org>
To:     <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <live-patching@...r.kernel.org>
CC:     <daniel@...earbox.net>, <kernel-team@...com>, <jolsa@...nel.org>,
        <rostedt@...dmis.org>, Song Liu <song@...nel.org>
Subject: [PATCH v4 bpf-next 0/4] ftrace: host klp and bpf trampoline together

Changes v3 => v4:
1. Fix build errors for different config. (kernel test robot)

Changes v2 => v3:
1. Major rewrite after discussions with Steven Rostedt. [1]
2. Remove SHARE_IPMODIFY flag from ftrace code. Instead use the callback
   function to communicate this information. (Steven)
3. Add cleanup_direct_functions_after_ipmodify() to clear SHARE_IPMODIFY
   on the DIRECT ops when the IPMODIFY ops is removed.

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 IPMODIFY ftrace_ops and one DIRECT ftrace_ops on the same kernel
function at the same time. Please see patch 2 and 4 for more details.

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.

[1] https://lore.kernel.org/all/20220602193706.2607681-2-song@kernel.org/

Jiri Olsa (1):
  bpf, x64: Allow to use caller address from stack

Song Liu (3):
  ftrace: add modify_ftrace_direct_multi_nolock
  ftrace: allow IPMODIFY and DIRECT ops on the same function
  bpf: support bpf_trampoline on functions with IPMODIFY (e.g.
    livepatch)

 arch/x86/net/bpf_jit_comp.c |  13 +-
 include/linux/bpf.h         |  13 ++
 include/linux/ftrace.h      |  43 +++++
 kernel/bpf/trampoline.c     | 158 +++++++++++++++++--
 kernel/trace/ftrace.c       | 306 +++++++++++++++++++++++++++++++-----
 5 files changed, 473 insertions(+), 60 deletions(-)

--
2.30.2