Patch "x86/ibt,ftrace: Search for __fentry__ location" has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

    x86/ibt,ftrace: Search for __fentry__ location

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-ibt-ftrace-search-for-__fentry__-location.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0fb3ba2981bdfeed49e23a1f6c7b020405952b3b
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Tue Mar 8 16:30:29 2022 +0100

    x86/ibt,ftrace: Search for __fentry__ location
    
    [ Upstream commit aebfd12521d9c7d0b502cf6d06314cfbcdccfe3b ]
    
    Currently a lot of ftrace code assumes __fentry__ is at sym+0. However
    with Intel IBT enabled the first instruction of a function will most
    likely be ENDBR.
    
    Change ftrace_location() to not only return the __fentry__ location
    when called for the __fentry__ location, but also when called for the
    sym+0 location.
    
    Then audit/update all callsites of this function to consistently use
    these new semantics.
    
    Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220308154318.227581603@xxxxxxxxxxxxx
    Stable-dep-of: e60b613df8b6 ("ftrace: Fix possible use-after-free issue in ftrace_location()")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 893f040b97b7d..99dd504307fdc 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -194,17 +194,10 @@ static unsigned long
 __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
 {
 	struct kprobe *kp;
-	unsigned long faddr;
+	bool 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))
-		return 0UL;
+	faddr = ftrace_location(addr) == addr;
 	/*
 	 * Use the current code if it is not modified by Kprobe
 	 * and it cannot be modified by ftrace.
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 4fa75791b45e2..1bffee0458863 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -108,18 +108,6 @@ static void bpf_trampoline_module_put(struct bpf_trampoline *tr)
 	tr->mod = NULL;
 }
 
-static int is_ftrace_location(void *ip)
-{
-	long addr;
-
-	addr = ftrace_location((long)ip);
-	if (!addr)
-		return 0;
-	if (WARN_ON_ONCE(addr != (long)ip))
-		return -EFAULT;
-	return 1;
-}
-
 static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
 {
 	void *ip = tr->func.addr;
@@ -151,12 +139,12 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad
 static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 {
 	void *ip = tr->func.addr;
+	unsigned long faddr;
 	int ret;
 
-	ret = is_ftrace_location(ip);
-	if (ret < 0)
-		return ret;
-	tr->func.ftrace_managed = ret;
+	faddr = ftrace_location((unsigned long)ip);
+	if (faddr)
+		tr->func.ftrace_managed = true;
 
 	if (bpf_trampoline_module_get(tr))
 		return -ENOENT;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index af57705e1fef3..258d425b2c4a5 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1526,14 +1526,10 @@ static inline int warn_kprobe_rereg(struct kprobe *p)
 
 int __weak arch_check_ftrace_location(struct kprobe *p)
 {
-	unsigned long ftrace_addr;
+	unsigned long addr = (unsigned long)p->addr;
 
-	ftrace_addr = ftrace_location((unsigned long)p->addr);
-	if (ftrace_addr) {
+	if (ftrace_location(addr) == addr) {
 #ifdef CONFIG_KPROBES_ON_FTRACE
-		/* Given address is not on the instruction boundary */
-		if ((unsigned long)p->addr != ftrace_addr)
-			return -EILSEQ;
 		p->flags |= KPROBE_FLAG_FTRACE;
 #else	/* !CONFIG_KPROBES_ON_FTRACE */
 		return -EINVAL;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 157a1d2d9802f..3dce1a107a7c7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1575,17 +1575,34 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 }
 
 /**
- * ftrace_location - return true if the ip giving is a traced location
+ * ftrace_location - return the ftrace location
  * @ip: the instruction pointer to check
  *
- * Returns rec->ip if @ip given is a pointer to a ftrace location.
- * That is, the instruction that is either a NOP or call to
- * the function tracer. It checks the ftrace internal tables to
- * determine if the address belongs or not.
+ * If @ip matches the ftrace location, return @ip.
+ * If @ip matches sym+0, return sym's ftrace location.
+ * Otherwise, return 0.
  */
 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;
+
+		/* map sym+0 to __fentry__ */
+		if (!offset)
+			rec = lookup_rec(ip, ip + size - 1);
+	}
+
+	if (rec)
+		return rec->ip;
+
+out:
+	return 0;
 }
 
 /**
@@ -4942,7 +4959,8 @@ 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) {
@@ -5090,11 +5108,16 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 	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;
 
@@ -5223,6 +5246,10 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
 
 	mutex_lock(&direct_mutex);
 
+	ip = ftrace_location(ip);
+	if (!ip)
+		goto out_unlock;
+
 	entry = find_direct_entry(&ip, NULL);
 	if (!entry)
 		goto out_unlock;
@@ -5354,6 +5381,11 @@ int modify_ftrace_direct(unsigned long ip,
 	mutex_lock(&direct_mutex);
 
 	mutex_lock(&ftrace_lock);
+
+	ip = ftrace_location(ip);
+	if (!ip)
+		goto out_unlock;
+
 	entry = find_direct_entry(&ip, &rec);
 	if (!entry)
 		goto out_unlock;




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