[v2,08/20] x86/ftrace: set trampoline pages as executable
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Message ID 20190129003422.9328-9-rick.p.edgecombe@intel.com
State New
Headers show
Series
  • Merge text_poke fixes and executable lockdowns
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Commit Message

Edgecombe, Rick P Jan. 29, 2019, 12:34 a.m. UTC
From: Nadav Amit <namit@vmware.com>

Since alloc_module() will not set the pages as executable soon, we need
to do so for ftrace trampoline pages after they are allocated.

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

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

Patch
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diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 8257a59704ae..13c8249b197f 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -742,6 +742,7 @@  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;
@@ -774,6 +775,7 @@  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);
@@ -818,6 +820,12 @@  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);