linux-kernel - [PATCH 3/3] kprobes: Allow probing on any address belonging to ftrace

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Message-Id: <78480d05821d45e09fb234f61f9037e26d42f02d.1645096227.git.naveen.n.rao@linux.vnet.ibm.com>
Date:   Thu, 17 Feb 2022 17:06:25 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Nicholas Piggin <npiggin@...il.com>, <bpf@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/3] kprobes: Allow probing on any address belonging to ftrace

On certain architectures, ftrace can reserve multiple instructions at
function entry. Rather than rejecting kprobe on addresses other than the
exact ftrace call instruction, use the address returned by ftrace to
probe at the correct address when CONFIG_KPROBES_ON_FTRACE is enabled.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 kernel/kprobes.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 94cab8c9ce56cc..0a797ede3fdf37 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1497,6 +1497,10 @@ bool within_kprobe_blacklist(unsigned long addr)
 static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
 			const char *symbol_name, unsigned int offset)
 {
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	unsigned long ftrace_addr = 0;
+#endif
+
 	if ((symbol_name && addr) || (!symbol_name && !addr))
 		goto invalid;
 
@@ -1507,6 +1511,14 @@ static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
 	}
 
 	addr = (kprobe_opcode_t *)(((char *)addr) + offset);
+
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	if (addr)
+		ftrace_addr = ftrace_location((unsigned long)addr);
+	if (ftrace_addr)
+		return (kprobe_opcode_t *)ftrace_addr;
+#endif
+
 	if (addr)
 		return addr;
 
-- 
2.35.1