linux-kernel - Re: [PATCH 04/29] x86/livepatch: Validate __fentry_

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Date:   Wed, 23 Feb 2022 11:57:26 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 04/29] x86/livepatch: Validate __fentry__ location

On Wed, Feb 23, 2022 at 11:09:44AM +0100, Peter Zijlstra wrote:
> Yes.. so yesterday, when making function-graph tracing not explode, I
> ran into a similar issue. Steve suggested something along the lines of
> .... this.
> 
> (modified from his actual suggestion to also cover this case)
> 
> Let me go try this...

This one actually works...

---
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1578,7 +1578,23 @@ unsigned long ftrace_location_range(unsi
  */
 unsigned long ftrace_location(unsigned long ip)
 {
-	return ftrace_location_range(ip, ip);
+	struct dyn_ftrace *rec;
+	unsigned long offset;
+	unsigned long size;
+
+	rec = lookup_rec(ip, ip);
+	if (!rec) {
+		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
+			goto out;
+
+		rec = lookup_rec(ip - offset, (ip - offset) + size);
+	}
+
+	if (rec)
+		return rec->ip;
+
+out:
+	return 0;
 }
 
 /**
@@ -5110,11 +5126,16 @@ int register_ftrace_direct(unsigned long
 	struct ftrace_func_entry *entry;
 	struct ftrace_hash *free_hash = NULL;
 	struct dyn_ftrace *rec;
-	int ret = -EBUSY;
+	int ret = -ENODEV;
 
 	mutex_lock(&direct_mutex);
 
+	ip = ftrace_location(ip);
+	if (!ip)
+		goto out_unlock;
+
 	/* See if there's a direct function at @ip already */
+	ret = -EBUSY;
 	if (ftrace_find_rec_direct(ip))
 		goto out_unlock;
 
@@ -5222,6 +5243,10 @@ int unregister_ftrace_direct(unsigned lo
 
 	mutex_lock(&direct_mutex);
 
+	ip = ftrace_location(ip);
+	if (!ip)
+		goto out_unlock;
+
 	entry = find_direct_entry(&ip, NULL);
 	if (!entry)
 		goto out_unlock;