Re: [kvm-unit-tests RFC 1/3] lib: s390x: sclp: Add carriage return to line feed

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Fri, 30 Jun 2023 14:54:47 +0000
Janosch Frank <frankja@linux.ibm.com> wrote:

> Without the \r the output of the ASCII console takes a lot of
> additional effort to read in comparison to the line mode console.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  lib/s390x/sclp-console.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/s390x/sclp-console.c b/lib/s390x/sclp-console.c
> index 19c74e46..384080b0 100644
> --- a/lib/s390x/sclp-console.c
> +++ b/lib/s390x/sclp-console.c
> @@ -97,14 +97,27 @@ static void sclp_print_ascii(const char *str)
>  {
>  	int len = strlen(str);
>  	WriteEventData *sccb = (void *)_sccb;
> +	char *str_dest = (char *)&sccb->msg;
> +	int i = 0;
>  
>  	sclp_mark_busy();
>  	memset(sccb, 0, sizeof(*sccb));
> +
> +	for (; i < len; i++) {
> +		*str_dest = str[i];
> +		str_dest++;
> +		/* Add a \r to the \n */
> +		if (str[i] == '\n') {
> +			*str_dest = '\r';
> +			str_dest++;
> +		}
> +	}
> +
> +	len = (uintptr_t)str_dest - (uintptr_t)&sccb->msg;

some strings will therefore potentially overflow the SCCB

sclp_print() refuses to print more than 2kB, with this patch that limit
could potentially be crossed

can you please briefly explain in a comment why that is ok? (or maybe
that is not ok? then fix it somehow :) )

>  	sccb->h.length = offsetof(WriteEventData, msg) + len;
>  	sccb->h.function_code = SCLP_FC_NORMAL_WRITE;
>  	sccb->ebh.length = sizeof(EventBufferHeader) + len;
>  	sccb->ebh.type = SCLP_EVENT_ASCII_CONSOLE_DATA;
> -	memcpy(&sccb->msg, str, len);
>  
>  	sclp_service_call(SCLP_CMD_WRITE_EVENT_DATA, sccb);
>  }