linux-kernel - [PATCH] kprobes: Call check_ftrace_location() on CONFIG_KPROBES_ON

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Message-Id: <20251205092933.3889547-1-qingwei.hu@bytedance.com>
Date: Fri,  5 Dec 2025 17:29:33 +0800
From: "qingwei.hu" <qingwei.hu@...edance.com>
To: naveen@...nel.org,
	davem@...emloft.net,
	mhiramat@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Qingwei Hu <qingwei.hu@...edance.com>
Subject: [PATCH] kprobes: Call check_ftrace_location() on CONFIG_KPROBES_ON_FTRACE

From: Qingwei Hu <qingwei.hu@...edance.com>

There is a possible configuration dependency:

  KPROBES_ON_FTRACE [=n]
       ^----- KPROBES [=y]
         |--- HAVE_KPROBES_ON_FTRACE [=n]
         |--- DYNAMIC_FTRACE_WITH_REGS [=n]
                ^----- FTRACE [=y]
                  |--- DYNAMIC_FTRACE [=y]
                  |--- HAVE_DYNAMIC_FTRACE_WITH_REGS [=n]

With DYNAMIC_FTRACE=y, ftrace_location() is meaningful and may
return the same address as the probe target.

However, when KPROBES_ON_FTRACE=n, the current implementation
returns -EINVAL after calling check_ftrace_location(), causing
the validation to fail.

Adjust the logic so that ftrace-based checks are performed only
when CONFIG_KPROBES_ON_FTRACE is enabled, ensuring correct
kprobe behavior even when KPROBES_ON_FTRACE=n.

Signed-off-by: Qingwei Hu <qingwei.hu@...edance.com>
---
 kernel/kprobes.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index ab8f9fc1f0d1..f4aa4ba1ca9c 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1512,19 +1512,15 @@ static inline int warn_kprobe_rereg(struct kprobe *p)
 	return 0;
 }
 
-static int check_ftrace_location(struct kprobe *p)
+#ifdef CONFIG_KPROBES_ON_FTRACE
+static void check_ftrace_location(struct kprobe *p)
 {
 	unsigned long addr = (unsigned long)p->addr;
 
-	if (ftrace_location(addr) == addr) {
-#ifdef CONFIG_KPROBES_ON_FTRACE
+	if (ftrace_location(addr) == addr)
 		p->flags |= KPROBE_FLAG_FTRACE;
-#else
-		return -EINVAL;
-#endif
-	}
-	return 0;
 }
+#endif
 
 static bool is_cfi_preamble_symbol(unsigned long addr)
 {
@@ -1540,11 +1536,9 @@ static bool is_cfi_preamble_symbol(unsigned long addr)
 static int check_kprobe_address_safe(struct kprobe *p,
 				     struct module **probed_mod)
 {
-	int ret;
-
-	ret = check_ftrace_location(p);
-	if (ret)
-		return ret;
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	check_ftrace_location(p);
+#endif
 
 	guard(jump_label_lock)();
 
-- 
2.39.5