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SubjectRe: [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;
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