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Date: Thu, 3 Mar 2022 16:59:03 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
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,
Masami Hiramatsu <mhiramat@...nel.org>,
ndesaulniers@...gle.com, samitolvanen@...gle.com, x86@...nel.org
Subject: Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location
On Thu, Mar 03, 2022 at 09:34:13AM -0500, Steven Rostedt wrote:
> On Thu, 3 Mar 2022 14:04:52 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
>
> > > @@ -1596,7 +1596,7 @@ static int check_ftrace_location(struct kprobe *p)
> > > {
> > > unsigned long ftrace_addr;
> > >
> > > - ftrace_addr = ftrace_location((unsigned long)p->addr);
> > > + ftrace_addr = ftrace_location_range((unsigned long)p->addr, (unsigned long)p->addr);
> >
> > Yes, although perhaps a new helper. I'll go ponder during lunch.
>
> Is there more places to add that to make it worth creating a helper?
This is what I ended up with, I've looked at all ftrace_location() sites
there are, seems to work too, both the built-in boot time ftrace tests
and the selftests work splat-less.
I should update the Changelog some though.
Naveen also mentioned register_ftrace_direct() could be further cleaned
up, but I didn't want to do too much in once go.
---
Subject: x86/ibt,ftrace: Search for __fentry__ location
From: Peter Zijlstra <peterz@...radead.org>
Date: Wed Feb 23 10:01:38 CET 2022
Have ftrace_location() search the symbol for the __fentry__ location
when it isn't at func+0 and use this for {,un}register_ftrace_direct().
This avoids a whole bunch of assumptions about __fentry__ being at
func+0.
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/kernel/kprobes/core.c | 11 +---------
kernel/bpf/trampoline.c | 20 +++----------------
kernel/kprobes.c | 8 +------
kernel/trace/ftrace.c | 43 +++++++++++++++++++++++++++++++++--------
4 files changed, 43 insertions(+), 39 deletions(-)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -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.
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -117,18 +117,6 @@ static void bpf_trampoline_module_put(st
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_tram
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;
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1562,14 +1562,10 @@ static inline int warn_kprobe_rereg(stru
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;
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1568,17 +1568,34 @@ unsigned long ftrace_location_range(unsi
}
/**
- * 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 *ha
{
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
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 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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