Re: [PATCH 08/17] x86/ftrace: set trampoline pages as executable

[Steven Rostedt]

On Wed, 6 Feb 2019 09:33:35 -0800
Nadav Amit <nadav.amit@xxxxxxxxx> wrote:


> >> 	/* 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?
> 

And I notice that it is set to RO after this call anyway.

-- Steve