Re: [PATCH v2] target/riscv: fix check of guest pa top bits

[Alistair Francis <alistair23@gmail.com>]

On Fri, May 1, 2020 at 11:51 AM Jose Martins <josemartins90@gmail.com> wrote:
>
> The spec states that on sv39x4 guest physical  "address bits 63:41 must
> all be zeros, or else a guest-page-fault exception occurs.".  However,
> the check performed for these top bits of the virtual address on the
> second stage is the same as the one performed for virtual addresses on
> the first stage except with the 2-bit extension, effectively creating
> the same kind of "hole" in the guest's physical address space. I believe
> the following patch fixes this issue:
>
> Signed-off-by: Jose Martins <josemartins90@gmail.com>

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

Applied to RISC-V tree.

Alistair

> ---
>  target/riscv/cpu_helper.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 247304d850..ae22c30bdd 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -426,15 +426,21 @@ static int get_physical_address(CPURISCVState *env, hwaddr *physical,
>      int va_bits = PGSHIFT + levels * ptidxbits + widened;
>      target_ulong mask, masked_msbs;
>
> -    if (TARGET_LONG_BITS > (va_bits - 1)) {
> -        mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
> +    if (!first_stage) {
> +        if ((addr >> va_bits) != 0) {
> +            return TRANSLATE_FAIL;
> +        }
>      } else {
> -        mask = 0;
> -    }
> -    masked_msbs = (addr >> (va_bits - 1)) & mask;
> +        if (TARGET_LONG_BITS > (va_bits - 1)) {
> +            mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
> +        } else {
> +            mask = 0;
> +        }
> +        masked_msbs = (addr >> (va_bits - 1)) & mask;
>
> -    if (masked_msbs != 0 && masked_msbs != mask) {
> -        return TRANSLATE_FAIL;
> +        if (masked_msbs != 0 && masked_msbs != mask) {
> +            return TRANSLATE_FAIL;
> +        }
>      }
>
>      int ptshift = (levels - 1) * ptidxbits;
> --
> 2.25.1
>
>