Re: [PATCH 2/4] arm64: usercopy: implement arch_within_stack_frames

[Kees Cook]

On Thu, Mar 1, 2018 at 2:19 AM,  <kpark3469@xxxxxxxxx> wrote:
> From: James Morse <james.morse@xxxxxxx>
>
> This implements arch_within_stack_frames() for arm64 that should
> validate if a given object is contained by a kernel stack frame.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Reviewed-by: Sahara <keun-o.park@xxxxxxxxxxxxx>

Looks good to me. Does this end up passing the LKDTM
USERCOPY_STACK_FRAME_TO and USERCOPY_STACK_FRAME_FROM tests?

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/arm64/Kconfig             |  1 +
>  arch/arm64/kernel/stacktrace.c | 76 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 77 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 5361287..b6c3b52 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -127,6 +127,7 @@ config ARM64
>         select HAVE_SYSCALL_TRACEPOINTS
>         select HAVE_KPROBES
>         select HAVE_KRETPROBES
> +       select HAVE_ARCH_WITHIN_STACK_FRAMES
>         select IOMMU_DMA if IOMMU_SUPPORT
>         select IRQ_DOMAIN
>         select IRQ_FORCED_THREADING
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index fbc366d..6d37fad 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -26,6 +26,11 @@
>  #include <asm/irq.h>
>  #include <asm/stack_pointer.h>
>
> +#define FAKE_FRAME(frame, my_func) do {                                \
> +       frame.fp = (unsigned long)__builtin_frame_address(0);   \
> +       frame.pc = (unsigned long)my_func;                      \
> +} while (0)
> +
>  /*
>   * AArch64 PCS assigns the frame pointer to x29.
>   *
> @@ -94,6 +99,77 @@ void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
>         }
>  }
>
> +struct check_frame_arg {
> +       unsigned long obj_start;
> +       unsigned long obj_end;
> +       unsigned long frame_start;
> +       int discard_frames;
> +       int err;
> +};
> +
> +static int check_frame(struct stackframe *frame, void *d)
> +{
> +       struct check_frame_arg *arg = d;
> +       unsigned long frame_end = frame->fp;
> +
> +       /* object overlaps multiple frames */
> +       if (arg->obj_start < frame->fp && frame->fp < arg->obj_end) {
> +               arg->err = BAD_STACK;
> +               return 1;
> +       }
> +
> +       /*
> +        * Discard frames and check object is in a frame written early
> +        * enough.
> +        */
> +       if (arg->discard_frames)
> +               arg->discard_frames--;
> +       else if ((arg->frame_start <= arg->obj_start &&
> +                       arg->obj_start < frame_end) &&
> +               (arg->frame_start < arg->obj_end && arg->obj_end <= frame_end))
> +               return 1;
> +
> +       /* object exists in a previous frame */
> +       if (arg->obj_end < arg->frame_start) {
> +               arg->err = BAD_STACK;
> +               return 1;
> +       }
> +
> +       arg->frame_start = frame_end + 0x10;
> +
> +       return 0;
> +}
> +
> +/* Check obj doesn't overlap a stack frame record */
> +int arch_within_stack_frames(const void *stack,
> +                            const void *stack_end,
> +                            const void *obj, unsigned long obj_len)
> +{
> +       struct stackframe frame;
> +       struct check_frame_arg arg;
> +
> +       if (!IS_ENABLED(CONFIG_FRAME_POINTER))
> +               return NOT_STACK;
> +
> +       arg.err = GOOD_FRAME;
> +       arg.obj_start = (unsigned long)obj;
> +       arg.obj_end = arg.obj_start + obj_len;
> +
> +       FAKE_FRAME(frame, arch_within_stack_frames);
> +       arg.frame_start = frame.fp;
> +
> +       /*
> +        * Skip 4 non-inlined frames: <fake frame>,
> +        * arch_within_stack_frames(), check_stack_object() and
> +        * __check_object_size().
> +        */
> +       arg.discard_frames = 4;
> +
> +       walk_stackframe(current, &frame, check_frame, &arg);
> +
> +       return arg.err;
> +}
> +
>  #ifdef CONFIG_STACKTRACE
>  struct stack_trace_data {
>         struct stack_trace *trace;
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security