linux-kernel - Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry_

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Message-ID: <20220302144716.1772020c@gandalf.local.home>
Date:   Wed, 2 Mar 2022 14:47:16 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        alexei.starovoitov@...il.com, alyssa.milburn@...el.com,
        andrew.cooper3@...rix.com, hjl.tools@...il.com,
        joao@...rdrivepizza.com, jpoimboe@...hat.com,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, mbenes@...e.cz, ndesaulniers@...gle.com,
        samitolvanen@...gle.com, x86@...nel.org
Subject: Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location

On Wed, 2 Mar 2022 11:01:38 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 2 Mar 2022 14:20:23 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Like so, or is something else needed?
> > 
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 68ecd3e35342..d1b30b5c5c23 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -4980,7 +4980,8 @@ ftrace_match_addr(struct ftrace_hash *hash, unsigned long ip, int remove)
> >  {
> >  	struct ftrace_func_entry *entry;
> >  
> > -	if (!ftrace_location(ip))
> > +	ip = ftrace_location(ip);
> > +	if (!ip)
> >  		return -EINVAL;  
> 
> This could possibly work. I'd have to test all this though.
> 
> I probably could just take this patch and try it out. You can remove the
> "x86/ibt" from the subject, as this patch may be a requirement for that
> (include that in the commit log), but it is has no changes to x86/ibt
> specifically.
> 

Note, I just pulled this patch, and I hit this warning:

WARNING: CPU: 0 PID: 6965 at arch/x86/kernel/kprobes/core.c:205 recover_probed_instruction+0x8f/0xa0

static unsigned long
__recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
        struct kprobe *kp;
        unsigned long faddr;

        kp = get_kprobe((void *)addr);
        faddr = ftrace_location(addr);
        /*
         * Addresses inside the ftrace location are refused by
         * arch_check_ftrace_location(). Something went terribly wrong
         * if such an address is checked here.
         */
        if (WARN_ON(faddr && faddr != addr))  <<---- HERE
                return 0UL;
        /*
         * Use the current code if it is not modified by Kprobe
         * and it cannot be modified by ftrace.
         */
        if (!kp && !faddr)
                return addr;

I guess this patch needs kprobe updates.

I'll pull down the latest tip and test that code.

-- Steve