[PATCH V2] x86/ftrace: Make sure that ftrace trampolines are not RWX

[Thomas Gleixner]

ftrace use module_alloc() to allocate trampoline pages. The mapping of
module_alloc() is RWX, which makes sense as the memory is written to right
after allocation. But nothing makes these pages RO after writing to them.

Add proper set_memory_rw/ro() calls to protect the trampolines after
modification.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
 arch/x86/kernel/ftrace.c |   20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -689,8 +689,12 @@ static inline void *alloc_tramp(unsigned
 {
        return module_alloc(size);
 }
-static inline void tramp_free(void *tramp)
+static inline void tramp_free(void *tramp, int size)
 {
+       int npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+       set_memory_nx((unsigned long)tramp, npages);
+       set_memory_rw((unsigned long)tramp, npages);
        module_memfree(tramp);
 }
 #else
@@ -699,7 +703,7 @@ static inline void *alloc_tramp(unsigned
 {
        return NULL;
 }
-static inline void tramp_free(void *tramp) { }
+static inline void tramp_free(void *tramp, int size) { }
 #endif
 
 /* Defined as markers to the end of the ftrace default trampolines */
@@ -771,7 +775,7 @@ create_trampoline(struct ftrace_ops *ops
        /* Copy ftrace_caller onto the trampoline memory */
        ret = probe_kernel_read(trampoline, (void *)start_offset, size);
        if (WARN_ON(ret < 0)) {
-               tramp_free(trampoline);
+               tramp_free(trampoline, *tramp_size);
                return 0;
        }
 
@@ -797,7 +801,7 @@ create_trampoline(struct ftrace_ops *ops
 
        /* Are we pointing to the reference? */
        if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0)) {
-               tramp_free(trampoline);
+               tramp_free(trampoline, *tramp_size);
                return 0;
        }
 
@@ -839,7 +843,7 @@ void arch_ftrace_update_trampoline(struc
        unsigned long offset;
        unsigned long ip;
        unsigned int size;
-       int ret;
+       int ret, npages;
 
        if (ops->trampoline) {
                /*
@@ -848,11 +852,14 @@ void arch_ftrace_update_trampoline(struc
                 */
                if (!(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
                        return;
+               npages = PAGE_ALIGN(ops->trampoline_size) >> PAGE_SHIFT;
+               set_memory_rw(ops->trampoline, npages);
        } else {
                ops->trampoline = create_trampoline(ops, &size);
                if (!ops->trampoline)
                        return;
                ops->trampoline_size = size;
+               npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
        }
 
        offset = calc_trampoline_call_offset(ops->flags & 
FTRACE_OPS_FL_SAVE_REGS);
@@ -863,6 +870,7 @@ void arch_ftrace_update_trampoline(struc
        /* Do a safe modify in case the trampoline is executing */
        new = ftrace_call_replace(ip, (unsigned long)func);
        ret = update_ftrace_func(ip, new);
+       set_memory_ro(ops->trampoline, npages);
 
        /* The update should never fail */
        WARN_ON(ret);
@@ -939,7 +947,7 @@ void arch_ftrace_trampoline_free(struct
        if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
                return;
 
-       tramp_free((void *)ops->trampoline);
+       tramp_free((void *)ops->trampoline, ops->trampoline_size);
        ops->trampoline = 0;
 }