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

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