From: Jonathan Gray <jsg@jsg.id.au>
Subject: Re: Avoid implicit sign extension in vctrap()
To: tech@openbsd.org
Date: Sun, 3 Aug 2025 09:37:21 +1000

On Sat, Aug 02, 2025 at 11:24:04PM +0200, Hans-Jörg Höxer wrote:
> Hi,
> 
> found by coverty:
>     
>     port is uint16_t.  Shifting promotes to signed 32bit integer.
>     When assigning to uint64_t sw_exitinfo1 the value gets sign extended.
>     Thus when "port << 16" is greater than 0x7fffffff the upper bits
>     of sw_exitinfo1 will be all 1.  Therefore cast to uint64_t before
>     shifting.
> 
> ok?

or make port uint64_t and drop the casts?

> 
> HJ.
> 
> -----------------------------------------------------------------------
> commit 0bdf00d115852dabeb9078497d91e19d8667898f
> Author: Hans-Joerg Hoexer <hshoexer@genua.de>
> Date:   Sat Aug 2 23:04:22 2025 +0200
> 
>     Avoid implicit sign extension in vctrap()
>     
>     port is uint16_t.  Shifting promotes to signed 32bit integer.  When
>     assigning to uint64_t sw_exitinfo1 the value gets sign extended.
>     Thus when "port << 16" is greater than 0x7fffffff the upper bits
>     of sw_exitinfo1 will be all 1.  Therefore apply cast to uint64_t
>     before shifting.
>     
>     Coverity CID 1648416.
> 
> diff --git a/sys/arch/amd64/amd64/trap.c b/sys/arch/amd64/amd64/trap.c
> index cb152600dca..dcdfd98c909 100644
> --- a/sys/arch/amd64/amd64/trap.c
> +++ b/sys/arch/amd64/amd64/trap.c
> @@ -367,14 +367,14 @@ vctrap(struct trapframe *frame, int user)
>  			case 0xef:	/* out %ax,(%dx) */
>  				ghcb_sync_val(GHCB_RAX, GHCB_SZ16, &syncout);
>  				port = (uint16_t)frame->tf_rdx;
> -				sw_exitinfo1 = (port << 16) |
> +				sw_exitinfo1 = ((uint64_t)port << 16) |
>  				    (1ULL << 5);
>  				frame->tf_rip += 2;
>  				break;
>  			case 0xed:	/* in (%dx),%ax */
>  				ghcb_sync_val(GHCB_RAX, GHCB_SZ16, &syncin);
>  				port = (uint16_t)frame->tf_rdx;
> -				sw_exitinfo1 = (port << 16) |
> +				sw_exitinfo1 = ((uint64_t)port << 16) |
>  				    (1ULL << 5) | (1ULL << 0);
>  				frame->tf_rip += 2;
>  				break;
> @@ -386,40 +386,40 @@ vctrap(struct trapframe *frame, int user)
>  		case 0xe4:	/* in $port,%al */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ8, &syncin);
>  			port = *(rip + 1);
> -			sw_exitinfo1 = (port << 16) | (1ULL << 4) |
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 4) |
>  			    (1ULL << 0);
>  			frame->tf_rip += 2;
>  			break;
>  		case 0xe6:	/* outb %al,$port */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ8, &syncout);
>  			port = *(rip + 1);
> -			sw_exitinfo1 = (port << 16) | (1ULL << 4);
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 4);
>  			frame->tf_rip += 2;
>  			break;
>  		case 0xec:	/* in (%dx),%al */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ8, &syncin);
>  			port = (uint16_t)frame->tf_rdx;
> -			sw_exitinfo1 = (port << 16) | (1ULL << 4) |
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 4) |
>  			    (1ULL << 0);
>  			frame->tf_rip += 1;
>  			break;
>  		case 0xed:	/* in (%dx),%eax */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ32, &syncin);
>  			port = (uint16_t)frame->tf_rdx;
> -			sw_exitinfo1 = (port << 16) | (1ULL << 6) |
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 6) |
>  			    (1ULL << 0);
>  			frame->tf_rip += 1;
>  			break;
>  		case 0xee:	/* out %al,(%dx) */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ8, &syncout);
>  			port = (uint16_t)frame->tf_rdx;
> -			sw_exitinfo1 = (port << 16) | (1ULL << 4);
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 4);
>  			frame->tf_rip += 1;
>  			break;
>  		case 0xef:	/* out %eax,(%dx) */
>  			ghcb_sync_val(GHCB_RAX, GHCB_SZ32, &syncout);
>  			port = (uint16_t)frame->tf_rdx;
> -			sw_exitinfo1 = (port << 16) | (1ULL << 6);
> +			sw_exitinfo1 = ((uint64_t)port << 16) | (1ULL << 6);
>  			frame->tf_rip += 1;
>  			break;
>  		default: