linux-kernel - [BUGFIX PATCH] kprobes/x86: Fix to set RWX bits correctly before releasing trampoline

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Message-Id: <149570868652.3518.14120169373590420503.stgit@devbox>
Date:   Thu, 25 May 2017 19:38:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [BUGFIX PATCH] kprobes/x86: Fix to set RWX bits correctly before releasing trampoline

Fix kprobes to set(recover) RWX bits correctly on trampoline
buffer before releasing it. Releasing readonly page to
module_memfree() crash the kernel.

Without this fix, if kprobes user register a bunch of kprobes
in function body (since kprobes on function entry usually
use ftrace) and unregister it, kernel hits a BUG and crash.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Fixes: d0381c81c2f7 ("kprobes/x86: Set kprobes pages read-only")
---
 arch/x86/kernel/kprobes/core.c |    9 +++++++++
 kernel/kprobes.c               |    2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 5b2bbfb..6b87780 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -52,6 +52,7 @@
 #include <linux/ftrace.h>
 #include <linux/frame.h>
 #include <linux/kasan.h>
+#include <linux/moduleloader.h>
 
 #include <asm/text-patching.h>
 #include <asm/cacheflush.h>
@@ -417,6 +418,14 @@ static void prepare_boost(struct kprobe *p, struct insn *insn)
 	}
 }
 
+/* Recover page to RW mode before releasing it */
+void free_insn_page(void *page)
+{
+	set_memory_nx((unsigned long)page & PAGE_MASK, 1);
+	set_memory_rw((unsigned long)page & PAGE_MASK, 1);
+	module_memfree(page);
+}
+
 static int arch_copy_kprobe(struct kprobe *p)
 {
 	struct insn insn;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9f60567..6756d75 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -122,7 +122,7 @@ static void *alloc_insn_page(void)
 	return module_alloc(PAGE_SIZE);
 }
 
-static void free_insn_page(void *page)
+void __weak free_insn_page(void *page)
 {
 	module_memfree(page);
 }