On Thu, 25 May 2017 12:51:21 -0700 Kees Cook <[email protected]> wrote:
> On Thu, May 25, 2017 at 10:46 AM, Luis R. Rodriguez <[email protected]> wrote: > > On Thu, May 25, 2017 at 10:57:51AM +0200, Thomas Gleixner wrote: > >> 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 <[email protected]> > >> --- > >> 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); > >> } > > > > Can/should module_memfree() just do this for users? With Masami's fix that'd > > be 2 users already. > > It seems like it really should. That would put it in a single place > and avoid this mistake again in the future. Does module_memfree() have > access to the allocation size, or does that need to get plumbed? module_memfree() is just a wrapper of vfree, so find_vm_area() will help us to get the size. Thank you, > > -Kees > > -- > Kees Cook > Pixel Security -- Masami Hiramatsu <[email protected]>
