Re: [PATCH v2] riscv: Make sure an exception is raised if a pte is malformed

[Alistair Francis]

On Wed, Apr 19, 2023 at 8:48 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> As per the privileged specification, in 64-bit, if any of the pte reserved
> bits 60-54 is set an exception should be triggered, and the same applies to
> napot/pbmt bits if those extensions are not enabled
> (see 4.4.1, "Addressing and Memory Protection").
>
> Reported-by: Andrea Parri <andrea@rivosinc.com>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

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

Alistair

> ---
>  target/riscv/cpu_bits.h   |  1 +
>  target/riscv/cpu_helper.c | 15 +++++++++++----
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index fca7ef0cef..8d9ba2ce11 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -640,6 +640,7 @@ typedef enum {
>  #define PTE_SOFT            0x300 /* Reserved for Software */
>  #define PTE_PBMT            0x6000000000000000ULL /* Page-based memory types 
> */
>  #define PTE_N               0x8000000000000000ULL /* NAPOT translation */
> +#define PTE_RESERVED        0x1FC0000000000000ULL /* Reserved bits */
>  #define PTE_ATTR            (PTE_N | PTE_PBMT) /* All attributes bits */
>
>  /* Page table PPN shift amount */
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index f88c503cf4..8dc832d1bb 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -946,13 +946,20 @@ restart:
>
>          if (riscv_cpu_sxl(env) == MXL_RV32) {
>              ppn = pte >> PTE_PPN_SHIFT;
> -        } else if (pbmte || cpu->cfg.ext_svnapot) {
> -            ppn = (pte & (target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT;
>          } else {
> -            ppn = pte >> PTE_PPN_SHIFT;
> -            if ((pte & ~(target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT) {
> +            if (pte & PTE_RESERVED) {
> +                return TRANSLATE_FAIL;
> +            }
> +
> +            if (!pbmte && (pte & PTE_PBMT)) {
>                  return TRANSLATE_FAIL;
>              }
> +
> +            if (!cpu->cfg.ext_svnapot && (pte & PTE_N)) {
> +                return TRANSLATE_FAIL;
> +            }
> +
> +            ppn = (pte & (target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT;
>          }
>
>          if (!(pte & PTE_V)) {
> --
> 2.37.2
>
>