Re: [PATCH v6 25/25] target/riscv: Reorg sum check in get_physical_address

[Alistair Francis]

On Sat, Mar 25, 2023 at 10:56 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Implement this by adjusting prot, which reduces the set of
> checks required.  This prevents exec to be set for U pages
> in MMUIdx_S_SUM.  While it had been technically incorrect,
> it did not manifest as a bug, because we will never attempt
> to execute from MMUIdx_S_SUM.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_helper.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 725ca45106..7336d1273b 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -800,7 +800,7 @@ static int get_physical_address(CPURISCVState *env, 
> hwaddr *physical,
>      *ret_prot = 0;
>
>      hwaddr base;
> -    int levels, ptidxbits, ptesize, vm, sum, widened;
> +    int levels, ptidxbits, ptesize, vm, widened;
>
>      if (first_stage == true) {
>          if (use_background) {
> @@ -831,7 +831,7 @@ static int get_physical_address(CPURISCVState *env, 
> hwaddr *physical,
>          }
>          widened = 2;
>      }
> -    sum = mmuidx_sum(mmu_idx);
> +
>      switch (vm) {
>      case VM_1_10_SV32:
>        levels = 2; ptidxbits = 10; ptesize = 4; break;
> @@ -999,15 +999,15 @@ restart:
>          prot |= PAGE_EXEC;
>      }
>
> -    if ((pte & PTE_U) &&
> -        ((mode != PRV_U) && (!sum || access_type == MMU_INST_FETCH))) {
> -        /*
> -         * User PTE flags when not U mode and mstatus.SUM is not set,
> -         * or the access type is an instruction fetch.
> -         */
> -        return TRANSLATE_FAIL;
> -    }
> -    if (!(pte & PTE_U) && (mode != PRV_S)) {
> +    if (pte & PTE_U) {
> +        if (mode != PRV_U) {
> +            if (!mmuidx_sum(mmu_idx)) {
> +                return TRANSLATE_FAIL;
> +            }
> +            /* SUM allows only read+write, not execute. */
> +            prot &= PAGE_READ | PAGE_WRITE;
> +        }
> +    } else if (mode != PRV_S) {
>          /* Supervisor PTE flags when not S mode */
>          return TRANSLATE_FAIL;
>      }
> --
> 2.34.1
>
>