linux-kernel - Re: [PATCH] kprobes: Call check_ftrace_location() on CONFIG_KPROBES_ON

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20251205100823.28aa8ffd@gandalf.local.home>
Date: Fri, 5 Dec 2025 10:08:23 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "qingwei.hu" <qingwei.hu@...edance.com>
Cc: naveen@...nel.org, davem@...emloft.net, mhiramat@...nel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: Call check_ftrace_location() on
 CONFIG_KPROBES_ON_FTRACE

On Fri,  5 Dec 2025 17:29:33 +0800
"qingwei.hu" <qingwei.hu@...edance.com> wrote:

> From: Qingwei Hu <qingwei.hu@...edance.com>
> 
> There is a possible configuration dependency:
> 
>   KPROBES_ON_FTRACE [=n]
>        ^----- KPROBES [=y]
>          |--- HAVE_KPROBES_ON_FTRACE [=n]
>          |--- DYNAMIC_FTRACE_WITH_REGS [=n]
>                 ^----- FTRACE [=y]
>                   |--- DYNAMIC_FTRACE [=y]
>                   |--- HAVE_DYNAMIC_FTRACE_WITH_REGS [=n]
> 
> With DYNAMIC_FTRACE=y, ftrace_location() is meaningful and may
> return the same address as the probe target.
> 
> However, when KPROBES_ON_FTRACE=n, the current implementation
> returns -EINVAL after calling check_ftrace_location(), causing
> the validation to fail.

This is a feature not a bug.

The reason is if you put a kprobe on a ftrace location, it can cause ftrace
to trigger a bug, as kprobes will modify the location and ftrace will see
something it doesn't expect and think the system is corrupted. We don't want
that either.

If you say "KPROBES_ON_FTRACE=n" and place a kprobe on a location that is
controlled by ftrace, it had better fail!

NAK

-- Steve