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Subject[tip: x86/core] x86/ibt,ftrace: Search for __fentry__ location
The following commit has been merged into the x86/core branch of tip:

Commit-ID: ee1a8cf8dd0f0b1a2adfb8aedf6c75568a411b0a
Gitweb: https://git.kernel.org/tip/ee1a8cf8dd0f0b1a2adfb8aedf6c75568a411b0a
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:29 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Mar 2022 23:53:31 +01:00

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: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.227581603@infradead.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(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6290712..4d8086a 100644
--- 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.
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 5e7edf9..455f1b4 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -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;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 94cab8c..6d1e11c 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -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;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a4b462b..ae0d9f6 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -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;
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