Re: [PATCH v3] tcg: Sanitize shift constants on ppc64le so that shift operations with large constants don't generate invalid instructions.

[Catherine A. Frederick / mptcultist]

Oh dear, I did it to myself again.

On Wed, Jun 3, 2020 at 7:13 PM <agrecascino123@gmail.com> wrote:
>
> From: "Catherine A. Frederick" <mptcultist@floorchan.org>
>
> Signed-off-by: Catherine A. Frederick <mptcultist@floorchan.org>
> ---
>  tcg/ppc/tcg-target.inc.c | 28 ++++++++++++++++++++++------
>  1 file changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/tcg/ppc/tcg-target.inc.c b/tcg/ppc/tcg-target.inc.c
> index 7da67086c6..3cab56fe91 100644
> --- a/tcg/ppc/tcg-target.inc.c
> +++ b/tcg/ppc/tcg-target.inc.c
> @@ -790,21 +790,25 @@ static inline void tcg_out_ext32u(TCGContext *s, TCGReg 
> dst, TCGReg src)
>
>  static inline void tcg_out_shli32(TCGContext *s, TCGReg dst, TCGReg src, int 
> c)
>  {
> +    tcg_debug_assert((c < 32) && (c >= 0));
>      tcg_out_rlw(s, RLWINM, dst, src, c, 0, 31 - c);
>  }
>
>  static inline void tcg_out_shli64(TCGContext *s, TCGReg dst, TCGReg src, int 
> c)
>  {
> +    tcg_debug_assert((c < 64) && (c >= 0));
>      tcg_out_rld(s, RLDICR, dst, src, c, 63 - c);
>  }
>
>  static inline void tcg_out_shri32(TCGContext *s, TCGReg dst, TCGReg src, int 
> c)
>  {
> +    tcg_debug_assert((c < 32) && (c >= 0));
>      tcg_out_rlw(s, RLWINM, dst, src, 32 - c, c, 31);
>  }
>
>  static inline void tcg_out_shri64(TCGContext *s, TCGReg dst, TCGReg src, int 
> c)
>  {
> +    tcg_debug_assert((c < 64) && (c >= 0));
>      tcg_out_rld(s, RLDICL, dst, src, 64 - c, c);
>  }
>
> @@ -2610,21 +2614,27 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc, 
> const TCGArg *args,
>
>      case INDEX_op_shl_i32:
>          if (const_args[2]) {
> -            tcg_out_shli32(s, args[0], args[1], args[2]);
> +            /* Limit shift immediate to prevent illegal instruction
> +               from bitmask corruption */
> +            tcg_out_shli32(s, args[0], args[1], args[2] & 31);
>          } else {
>              tcg_out32(s, SLW | SAB(args[1], args[0], args[2]));
>          }
>          break;
>      case INDEX_op_shr_i32:
>          if (const_args[2]) {
> -            tcg_out_shri32(s, args[0], args[1], args[2]);
> +            /* Both use RLWINM, which has a 5 bit field for the
> +               shift mask. */
> +            tcg_out_shri32(s, args[0], args[1], args[2] & 31);
>          } else {
>              tcg_out32(s, SRW | SAB(args[1], args[0], args[2]));
>          }
>          break;
>      case INDEX_op_sar_i32:
>          if (const_args[2]) {
> -            tcg_out32(s, SRAWI | RS(args[1]) | RA(args[0]) | SH(args[2]));
> +            /* SRAWI has a 5 bit sized field for the shift mask
> +               as well. */
> +            tcg_out32(s, SRAWI | RS(args[1]) | RA(args[0]) | SH(args[2] & 
> 31));
>          } else {
>              tcg_out32(s, SRAW | SAB(args[1], args[0], args[2]));
>          }
> @@ -2696,21 +2706,27 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc, 
> const TCGArg *args,
>
>      case INDEX_op_shl_i64:
>          if (const_args[2]) {
> -            tcg_out_shli64(s, args[0], args[1], args[2]);
> +            /* Limit shift immediate to prevent illegal instruction from
> +               from bitmask corruption */
> +            tcg_out_shli64(s, args[0], args[1], args[2] & 63);
>          } else {
>              tcg_out32(s, SLD | SAB(args[1], args[0], args[2]));
>          }
>          break;
>      case INDEX_op_shr_i64:
>          if (const_args[2]) {
> -            tcg_out_shri64(s, args[0], args[1], args[2]);
> +            /* Same applies here, as both RLDICL, and RLDICR have a
> +               6 bit large mask for the shift value */
> +            tcg_out_shri64(s, args[0], args[1], args[2] & 63);
>          } else {
>              tcg_out32(s, SRD | SAB(args[1], args[0], args[2]));
>          }
>          break;
>      case INDEX_op_sar_i64:
>          if (const_args[2]) {
> -            int sh = SH(args[2] & 0x1f) | (((args[2] >> 5) & 1) << 1);
> +            /* Same for SRADI, except there's no function
> +               to call into. */
> +            int sh = SH(((args[2] & 63) & 0x1f) | ((((args[2] & 63) >> 5) & 
> 1) << 1));
>              tcg_out32(s, SRADI | RA(args[0]) | RS(args[1]) | sh);
>          } else {
>              tcg_out32(s, SRAD | SAB(args[1], args[0], args[2]));
> --
> 2.26.2
>