Re: [PATCH 5/5] target/riscv/cpu_helper.c: fix bad_shift in riscv_cpu_interrupt()

[Alistair Francis]

On Wed, Jan 22, 2025 at 4:49 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Coverity reported a BAD_SHIFT issue in the following code:
>
>  > 2097
>  >>>>      CID 1590355:  Integer handling issues  (BAD_SHIFT)
>  >>>>      In expression "hdeleg >> cause", right shifting by more than 63
>        bits has undefined behavior.  The shift amount, "cause", is at least 
> 64.
>  > 2098         vsmode_exc = env->virt_enabled && (((hdeleg >> cause) & 1) || 
> vs_injected);
>  > 2099         /*
>
> It is not clear to me how the tool guarantees that '"cause" is at least
> 64', but indeed there's no guarantees that it would be < 64 in the
> 'async = true' code path.
>
> A simple fix to avoid a potential UB is to add a 'cause < 64' guard like
> 'mode' is already doing right before 'vsmode_exc'.
>
> Resolves: Coverity CID 1590355
> Fixes: 967760f62c ("target/riscv: Implement Ssdbltrp exception handling")
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

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

Alistair

> ---
>  target/riscv/cpu_helper.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index e1dfc4ecbf..64d1d68550 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -2095,7 +2095,9 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>      mode = env->priv <= PRV_S && cause < 64 &&
>          (((deleg >> cause) & 1) || s_injected || vs_injected) ? PRV_S : 
> PRV_M;
>
> -    vsmode_exc = env->virt_enabled && (((hdeleg >> cause) & 1) || 
> vs_injected);
> +    vsmode_exc = env->virt_enabled && cause < 64 &&
> +        (((hdeleg >> cause) & 1) || vs_injected);
> +
>      /*
>       * Check double trap condition only if already in S-mode and targeting
>       * S-mode
> --
> 2.47.1
>
>