linux-kernel - Re: [RFC PATCH v2 01/31] tracing: Add a comment about ftrace

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

Message-ID: <ZU4P45t-mDoyItg3@FVFF77S0Q05N>
Date:   Fri, 10 Nov 2023 11:11:31 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Florent Revest <revest@...omium.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alan Maguire <alan.maguire@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Guo Ren <guoren@...nel.org>
Subject: Re: [RFC PATCH v2 01/31] tracing: Add a comment about ftrace_regs
 definition

On Thu, Nov 09, 2023 at 08:14:52AM +0900, Masami Hiramatsu wrote:
> On Wed,  8 Nov 2023 23:24:32 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > To clarify what will be expected on ftrace_regs, add a comment to the
> > architecture independent definition of the ftrace_regs.
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > ---
> >  Changes in v2:
> >   - newly added.
> > ---
> >  include/linux/ftrace.h |   25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> > 
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index e8921871ef9a..b174af91d8be 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -118,6 +118,31 @@ extern int ftrace_enabled;
> >  
> >  #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> >  
> > +/**
> > + * ftrace_regs - ftrace partial/optimal register set
> > + *
> > + * ftrace_regs represents a group of registers which is used at the
> > + * function entry and exit. There are three types of registers.
> > + *
> > + * - Registers for passing the parameters to callee, including the stack
> > + *   pointer. (e.g. rcx, rdx, rdi, rsi, r8, r9 and rsp on x86_64)
> > + * - Registers for passing the return values to caller.
> > + *   (e.g. rax and rdx on x86_64)
> > + * - Registers for hooking the function return including the frame pointer
> > + *   (the frame pointer is architecture/config dependent)
> > + *   (e.g. rbp and rsp for x86_64)
> 
> Oops, I found the program counter/instruction pointer must be saved too.
> This is used for live patching. One question is that if the IP is modified
> at the return handler, what should we do? Return to the specified address?

I'm a bit confused here; currently we use fgraph_ret_regs for function returns,
are we going to replace that with ftrace_regs?

I think it makes sense for the PC/IP to be the address the return handler will
eventually return to (and hence allowing it to be overridden), but that does
mean we'll need to go recover the return address *before* we invoke any return
handlers.

Thanks,
Mark.