Re: [PATCH 04/11] powerpc: Don't negate error in syscall_set_return_value()

[Kees Cook]

On Thu, Jul 23, 2015 at 3:21 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> Currently the only caller of syscall_set_return_value() is seccomp
> filter, which is not enabled on powerpc.
>
> This means we have not noticed that our implementation of
> syscall_set_return_value() negates error, even though the value passed
> in is already negative.
>
> So remove the negation in syscall_set_return_value(), and expect the
> caller to do it like all other implementations do.
>
> Also add a comment about the ccr handling.
>
> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/powerpc/include/asm/syscall.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index c6239dabcfb1..cabe90133e69 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -44,9 +44,15 @@ static inline void syscall_set_return_value(struct task_struct *task,
>                                             struct pt_regs *regs,
>                                             int error, long val)
>  {
> +       /*
> +        * In the general case it's not obvious that we must deal with CCR
> +        * here, as the syscall exit path will also do that for us. However
> +        * there are some places, eg. the signal code, which check ccr to
> +        * decide if the value in r3 is actually an error.
> +        */
>         if (error) {
>                 regs->ccr |= 0x10000000L;
> -               regs->gpr[3] = -error;
> +               regs->gpr[3] = error;
>         } else {
>                 regs->ccr &= ~0x10000000L;
>                 regs->gpr[3] = val;
> --
> 2.1.0
>



-- 
Kees Cook
Chrome OS Security
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