Re: [PATCH 2/2] riscv: fix syscall_{get,set}_arguments

[Kees Cook <keescook@chromium.org>]

On Thu, Dec 6, 2018 at 7:02 AM David Abdurachmanov
<david.abdurachmanov@gmail.com> wrote:
>
> Testing with libseccomp master branch revealed that testcases with
> filters on syscall arguments were failing due to wrong values. Seccomp
> uses syscall_get_argumentsi() to copy syscall arguments, and there is a
> bug in pointer arithmetics in memcpy() call.
>
> Two alternative implementation were tested: the one in this patch and
> another one based on while-break loop. Both delivered the same results.
>
> This implementation is also used in arm, arm64 and nds32 arches.

Minor nit: can you make this the first patch? That way seccomp works
correctly from the point of introduction. :)

-Kees

>
> Signed-off-by: David Abdurachmanov <david.abdurachmanov@gmail.com>
> ---
>  arch/riscv/include/asm/syscall.h | 42 ++++++++++++++++++++++++--------
>  1 file changed, 32 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
> index bba3da6ef157..26ceb434a433 100644
> --- a/arch/riscv/include/asm/syscall.h
> +++ b/arch/riscv/include/asm/syscall.h
> @@ -70,19 +70,32 @@ static inline void syscall_set_return_value(struct task_struct *task,
>         regs->a0 = (long) error ?: val;
>  }
>
> +#define SYSCALL_MAX_ARGS 6
> +
>  static inline void syscall_get_arguments(struct task_struct *task,
>                                          struct pt_regs *regs,
>                                          unsigned int i, unsigned int n,
>                                          unsigned long *args)
>  {
> -       BUG_ON(i + n > 6);
> +       if (n == 0)
> +               return;
> +
> +       if (i + n > SYSCALL_MAX_ARGS) {
> +               unsigned long *args_bad = args + SYSCALL_MAX_ARGS - i;
> +               unsigned int n_bad = n + i - SYSCALL_MAX_ARGS;
> +               pr_warning("%s called with max args %d, handling only %d\n",
> +                       __func__, i + n, SYSCALL_MAX_ARGS);
> +               memset(args_bad, 0, n_bad * sizeof(args[0]));
> +       }
> +
>         if (i == 0) {
>                 args[0] = regs->orig_a0;
>                 args++;
>                 i++;
>                 n--;
>         }
> -       memcpy(args, &regs->a1 + i * sizeof(regs->a1), n * sizeof(args[0]));
> +
> +       memcpy(args, &regs->a0 + i, n * sizeof(args[0]));
>  }
>
>  static inline void syscall_set_arguments(struct task_struct *task,
> @@ -90,14 +103,23 @@ static inline void syscall_set_arguments(struct task_struct *task,
>                                          unsigned int i, unsigned int n,
>                                          const unsigned long *args)
>  {
> -       BUG_ON(i + n > 6);
> -        if (i == 0) {
> -                regs->orig_a0 = args[0];
> -                args++;
> -                i++;
> -                n--;
> -        }
> -       memcpy(&regs->a1 + i * sizeof(regs->a1), args, n * sizeof(regs->a0));
> +       if (n == 0)
> +               return;
> +
> +       if (i + n > SYSCALL_MAX_ARGS) {
> +               pr_warning("%s called with max args %d, handling only %d\n",
> +                       __func__, i + n, SYSCALL_MAX_ARGS);
> +               n = SYSCALL_MAX_ARGS - i;
> +       }
> +
> +       if (i == 0) {
> +               regs->orig_a0 = args[0];
> +               args++;
> +               i++;
> +               n--;
> +       }
> +
> +       memcpy(&regs->a0 + i, args, n * sizeof(args[0]));
>  }
>
>  static inline int syscall_get_arch(void)
> --
> 2.19.2
>


-- 
Kees Cook