On Wed, 16 Jan 2019 16:32:50 -0800 Rick Edgecombe <[email protected]> wrote:
> From: Nadav Amit <[email protected]> > > 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 <[email protected]> > Signed-off-by: Nadav Amit <[email protected]> > Signed-off-by: Rick Edgecombe <[email protected]> > --- > 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. As for this patch: Reviewed-by: Steven Rostedt (VMware) <[email protected]> -- Steve > + set_memory_x((unsigned long)trampoline, npages); > + > return (unsigned long)trampoline; > fail: > tramp_free(trampoline, *tramp_size);
