3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhira...@kernel.org>

commit c93f5cf571e7795f97d49ef51b766cf25e328545 upstream.

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.

Link: 
http://lkml.kernel.org/r/149570868652.3518.14120169373590420503.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
Fixes: d0381c81c2f7 ("kprobes/x86: Set kprobes pages read-only")
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
Cc: Ben Hutchings <ben.hutchi...@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/x86/kernel/kprobes/core.c |    9 +++++++++
 kernel/kprobes.c               |    2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -49,6 +49,7 @@
 #include <linux/kdebug.h>
 #include <linux/kallsyms.h>
 #include <linux/ftrace.h>
+#include <linux/moduleloader.h>
 
 #include <asm/cacheflush.h>
 #include <asm/desc.h>
@@ -374,6 +375,14 @@ int __copy_instruction(u8 *dest, u8 *src
        return length;
 }
 
+/* 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);
+       vfree(page);
+}
+
 static int arch_copy_kprobe(struct kprobe *p)
 {
        int ret;
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -125,7 +125,7 @@ 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_free(NULL, page);
 }


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