Re: [Qemu-devel] [PATCH v10 14/26] target-arm: respect SCR.FW, SCR.AW and SCTLR.NMFI

[Peter Maydell]

On 6 November 2014 15:51, Greg Bellows <address@hidden> wrote:
> From: Fabian Aggeler <address@hidden>
>
> Add checks of SCR AW/FW bits when performing writes of CPSR.  These SCR bits
> are used to control whether the CPSR masking bits can be adjusted from
> non-secure state.
>
> Signed-off-by: Fabian Aggeler <address@hidden>
> Signed-off-by: Greg Bellows <address@hidden>
>
> ---
>
> v8 -> v9
> - Move cpsr_write mask filtering above mode switch.
> - Replace conditional checks removed in v8.
>
> v7 -> v8
> - Fixed incorrect use of env->uncached_cpsr A/I/F to use env->daif instead.
> - Removed incorrect statement about SPSR to CPSR copies being affected by
>   SCR.AW/FW.
> - Fix typo in comment.
> - Simpified cpsr_write logic
>
> v3 -> v4
> - Fixed up conditions for ignoring CPSR.A/F updates by isolating to v7 and
>   checking for the existence of EL3 and non-existence of EL2.
> ---
>  target-arm/helper.c | 59 
> +++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 57 insertions(+), 2 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 948192b..9186fc7 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -3644,6 +3644,8 @@ uint32_t cpsr_read(CPUARMState *env)
>
>  void cpsr_write(CPUARMState *env, uint32_t val, uint32_t mask)
>  {
> +    uint32_t changed_daif;
> +
>      if (mask & CPSR_NZCV) {
>          env->ZF = (~val) & CPSR_Z;
>          env->NF = val;
> @@ -3666,8 +3668,57 @@ void cpsr_write(CPUARMState *env, uint32_t val, 
> uint32_t mask)
>          env->GE = (val >> 16) & 0xf;
>      }
>
> -    env->daif &= ~(CPSR_AIF & mask);
> -    env->daif |= val & CPSR_AIF & mask;
> +    /* In a V7 implementation that includes the security extensions but does
> +     * not include Virtualization Extensions the SCR.FW and SCR.AW bits 
> control
> +     * whether non-secure software is allowed to change the CPSR_F and CPSR_A
> +     * bits respectively.
> +     *
> +     * In a V8 implementation, it is permitted for privileged software to
> +     * change the CPSR A/F bits regardless of the SCR.AW/FW bits.
> +     */
> +    if (!arm_feature(env, ARM_FEATURE_V8) &&
> +        arm_feature(env, ARM_FEATURE_EL3) &&
> +        !arm_feature(env, ARM_FEATURE_EL2) &&
> +        !arm_is_secure(env)) {
> +
> +        changed_daif = (env->daif ^ val) & mask;
> +
> +        if (changed_daif & CPSR_A) {
> +            /* Check to see if we are allowed to change the masking of async
> +             * abort exceptions from a non-secure state.
> +             */
> +            if (!(env->cp15.scr_el3 & SCR_AW)) {
> +                qemu_log_mask(LOG_GUEST_ERROR,
> +                              "Ignoring attempt to switch CPSR_A flag from "
> +                              "non-secure world with SCR.AW bit clear\n");
> +                mask &= ~CPSR_A;
> +            }
> +        }
> +
> +        if (changed_daif & CPSR_F) {
> +            /* Check to see if we are allowed to change the masking of FIQ
> +             * exceptions from a non-secure state.
> +             */
> +            if (!(env->cp15.scr_el3 & SCR_FW)) {
> +                qemu_log_mask(LOG_GUEST_ERROR,
> +                              "Ignoring attempt to switch CPSR_F flag from "
> +                              "non-secure world with SCR.FW bit clear\n");
> +                mask &= ~CPSR_F;
> +            }
> +
> +            /* Check whether non-maskable FIQ (NMFI) support is enabled.
> +             * If this bit is set software is not allowed to mask
> +             * FIQs, but is allowed to set CPSR_F to 0.
> +             */
> +            if ((A32_BANKED_CURRENT_REG_GET(env, sctlr) & SCTLR_NMFI) &&
> +                (val & CPSR_F)) {
> +                qemu_log_mask(LOG_GUEST_ERROR,
> +                              "Ignoring attempt to enable CPSR_F flag "
> +                              "(non-maskable FIQ [NMFI] support enabled)\n");
> +                mask &= ~CPSR_F;
> +            }
> +        }
> +    }
>
>      if ((env->uncached_cpsr ^ val) & mask & CPSR_M) {
>          if (bad_mode_switch(env, val & CPSR_M)) {
> @@ -3680,6 +3731,10 @@ void cpsr_write(CPUARMState *env, uint32_t val, 
> uint32_t mask)
>              switch_mode(env, val & CPSR_M);
>          }
>      }
> +
> +    env->daif &= ~(CPSR_AIF & mask);
> +    env->daif |= val & CPSR_AIF & mask;
> +

Was moving this bit below the setting of the mode flags deliberate?
I don't see any reason why it has to go here. If you move it back
where it was then you can add my r-b tag.

>      mask &= ~CACHED_CPSR_BITS;
>      env->uncached_cpsr = (env->uncached_cpsr & ~mask) | (val & mask);
>  }

thanks
-- PMM