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

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Date:   Wed, 2 Mar 2022 14:20:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.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 Tue, Mar 01, 2022 at 02:20:16PM -0500, Steven Rostedt wrote:
> On Wed, 02 Mar 2022 00:27:51 +0530
> "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> 
> > Won't this cause issues with ftrace_set_filter_ip() and others? If the 
> > passed-in ip points to func+0 when the actual ftrace location is at some 
> > offset, the ftrace location check in ftrace_match_addr() will now pass, 
> > resulting in adding func+0 to the hash. Should we also update 
> > ftrace_match_addr() to use the ip returned by ftrace_location()?
> > 
> 
> Yes, ftrace_match_addr() would need to be updated, or at least
> ftrace_set_filter_ip() which is the only user ftrace_match_addr(), and is
> currently only used by kprobes, live kernel patching and the direct
> trampoline example code.

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;
 
 	if (remove) {