[PATCH v4 09/23] x86/ftrace: Set trampoline pages as executable

[Rick Edgecombe]

From: Nadav Amit <namit at vmware.com>

Since alloc_module() will not set the pages as executable soon, set
ftrace trampoline pages as executable after they are allocated.

For the time being, do not change ftrace to use the text_poke()
interface. As a result, ftrace still breaks W^X.

Reviewed-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
Signed-off-by: Nadav Amit <namit at vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe at intel.com>
---
 arch/x86/kernel/ftrace.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index ef49517f6bb2..53ba1aa3a01f 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -730,6 +730,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	unsigned long end_offset;
 	unsigned long op_offset;
 	unsigned long offset;
+	unsigned long npages;
 	unsigned long size;
 	unsigned long retq;
 	unsigned long *ptr;
@@ -762,6 +763,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 		return 0;
 
 	*tramp_size = size + RET_SIZE + sizeof(void *);
+	npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
 
 	/* Copy ftrace_caller onto the trampoline memory */
 	ret = probe_kernel_read(trampoline, (void *)start_offset, size);
@@ -806,6 +808,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	/* ALLOC_TRAMP flags lets us know we created it */
 	ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
 
+	/*
+	 * Module allocation needs to be completed by making the page
+	 * executable. The page is still writable, which is a security hazard,
+	 * but anyhow ftrace breaks W^X completely.
+	 */
+	set_memory_x((unsigned long)trampoline, npages);
 	return (unsigned long)trampoline;
 fail:
 	tramp_free(trampoline, *tramp_size);
-- 
2.17.1