[PATCH 4.19 68/73] x86/ftrace: Set trampoline pages as executable

From: Greg Kroah-Hartman
Date: Fri Jun 07 2019 - 11:50:54 EST

[ Upstream commit 3c0dab44e22782359a0a706cbce72de99a22aa75 ]

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.

Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: <ard.biesheuvel@xxxxxxxxxx>
Cc: <deneen.t.dock@xxxxxxxxx>
Cc: <kernel-hardening@xxxxxxxxxxxxxxxxxx>
Cc: <kristen@xxxxxxxxxxxxxxx>
Cc: <linux_dti@xxxxxxxxxx>
Cc: <will.deacon@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190426001143.4983-10-namit@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 38c798b1dbd2..9f033dfd2766 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -761,6 +761,7 @@ 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;
@@ -793,6 +794,7 @@ 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);
@@ -837,6 +839,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
/* ALLOC_TRAMP flags lets us know we created it */

+ /*
+ * 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;
tramp_free(trampoline, *tramp_size);