linux-kernel - [PATCH -tip v4 0/2] x86/kprobes: Fix to check not-kprobe's int3 correctly

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Date:   Mon, 19 Dec 2022 23:35:00 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     x86@...nel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        bpf <bpf@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Nadav Amit <namit@...are.com>
Subject: [PATCH -tip v4 0/2] x86/kprobes: Fix to check not-kprobe's int3 correctly

Hi,

Here is 4th version of the patches to fix kprobes and optprobe with
CONFIG_RETHUNK and CONFIG_SLS.
Previous version is here;

https://lore.kernel.org/all/166264927154.775585.16570756675363838701.stgit@devnote2/

I just ported the v3 on the latest -tip tree.

With CONFIG_RETHUNK/CONFIG_SLS and after many efforts, the kernel
functions may includes INT3 for stopping speculative execution in the
function code block (body) in addition to the gaps between functions.

Since kprobes on x86 has to ensure the probe address is an instruction
bondary, it decodes the instructions in the function until the address.
If it finds an INT3 which is not embedded by kprobe, it stops decoding
because usually the INT3 is used for debugging as a software breakpoint
and such INT3 will replace the first byte of an original instruction.
Thus the kprobes returns -EILSEQ as below.

 # echo 'p:probe/resched_curr_L21 resched_curr+98' >> dynamic_events 
 sh: write error: Invalid or incomplete multibyte or wide character

Actually, such INT3 can be ignored except the INT3 installed dynamically
by kgdb.
To avoid this issue, just check whether the INT3 is owned by kgdb
or not and if so, it just stopped and return failure.

With thses fixes, kprobe and optprobe can probe the kernel again with
CONFIG_RETHUNK=y.

Thank you,

---

Masami Hiramatsu (Google) (2):
      x86/kprobes: Fix kprobes instruction boudary check with CONFIG_RETHUNK
      x86/kprobes: Fix optprobe optimization check with CONFIG_RETHUNK

 arch/x86/kernel/kprobes/core.c |   10 +++++++---
 arch/x86/kernel/kprobes/opt.c  |   28 ++++++++--------------------
 2 files changed, 15 insertions(+), 23 deletions(-)

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>