Commit aebfd125 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86/ibt,ftrace: Search for __fentry__ location 



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: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.227581603@infradead.org
parent 6649fa87

arch/x86/kernel/kprobes/core.c

+2 −9
Original line number Diff line number Diff line
@@ -193,17 +193,10 @@ 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.

kernel/bpf/trampoline.c

+4 −16
Original line number Diff line number Diff line
@@ -117,18 +117,6 @@ 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;
@@ -160,12 +148,12 @@ 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;

kernel/kprobes.c

+2 −6
Original line number Diff line number Diff line
@@ -1562,14 +1562,10 @@ static inline int warn_kprobe_rereg(struct kprobe *p) 


static int 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;

kernel/trace/ftrace.c

+40 −8
Original line number Diff line number Diff line
@@ -1568,17 +1568,34 @@ 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;

}



/**
@@ -4962,7 +4979,8 @@ 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) {
@@ -5110,11 +5128,16 @@ 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;
@@ -5222,6 +5245,10 @@ 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;