On Feb 6, 2019, at 8:22 AM, Steven Rostedt [off-list ref] wrote:

On Wed, 16 Jan 2019 16:32:50 -0800
Rick Edgecombe [off-list ref] wrote:

quoted

From: Nadav Amit <redacted>

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 <redacted>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
arch/x86/kernel/ftrace.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 8257a59704ae..eb4a1937e72c 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 +820,13 @@ 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.
+	 */

Perhaps we should set the page to non writable after the page is
updated? And set it to writable only when we need to update it.

You remember that I sent you a patch that changed all these writes into
text_poke() and you said that I should defer it until this series is merged?

As for this patch:

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Thanks!