[PATCHv2] arm64: Rework valid_user_regs

[Peter Maydell]

On 12 February 2016 at 14:04, Mark Rutland <mark.rutland at arm.com> wrote:
> We validate pstate using PSR_MODE32_BIT, which is part of the
> user-provided pstate (and cannot be trusted). Also, we conflate
> validation of AArch32 and AArch64 pstate values, making the code
> difficult to reason about.
>
> Instead, validate the pstate value based on the associated task. The
> task may or may not be current (e.g. when using ptrace), so this must be
> passed explicitly by callers. To avoid circular header dependencies via
> sched.h, is_compat_task is pulled out of asm/ptrace.h.
>
> To make the code possible to reason about, the AArch64 and AArch32
> validation is split into separate functions. Software must respect the
> RES0 policy for SPSR bits, and thus the kernel mirrors the hardware
> policy (RAZ/WI) for bits as-yet unallocated. When these acquire an
> architected meaning writes may be permitted (potentially with additional
> validation).

> +       /* Force PSR to a valid 32-bit EL0t */
> +       regs->pstate |= PSR_MODE32_BIT;
> +       regs->pstate &= PSR_f | PSR_s | (PSR_x & ~COMPAT_PSR_A_BIT) | \
> +                       COMPAT_PSR_T_BIT;
> +

I think the consensus from the v1 review was to drop these PSR_[fsx] masks?

thanks
-- PMM