> On Feb 6, 2019, at 8:22 AM, Steven Rostedt <[email protected]> wrote: > > 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.
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) <[email protected]> Thanks!
