linux-kernel - Re: [PATCH 2/2] riscv: fix syscall_{get,set}

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Date:   Thu, 6 Dec 2018 18:13:52 +0100
From:   David Abdurachmanov <david.abdurachmanov@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>, aou@...s.berkeley.edu,
        luto@...capital.net, Will Drewry <wad@...omium.org>,
        Green Hu <green.hu@...il.com>, deanbo422@...il.com,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 2/2] riscv: fix syscall_{get,set}_arguments

On Thu, Dec 6, 2018 at 5:49 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Dec 6, 2018 at 7:02 AM David Abdurachmanov
> <david.abdurachmanov@...il.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. :)

Ok. I will do it.

david

>
> -Kees
>
> >
> > Signed-off-by: David Abdurachmanov <david.abdurachmanov@...il.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