Re: [Xen-devel] [PATCH] x86/HVM: make explicit that hvm_print_line() does output only

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/12/17 16:27, Jan Beulich wrote:
> On input "c" being 0xff should already have the effect of bailing early
> (due to the isprint()), but let's rather make this explicit. Also
> convert the BUG_ON() to an ASSERT() (nothing fatal happens in the
> function if this is violated), at the same time extending what is being
> checked.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -544,10 +544,14 @@ static int hvm_print_line(
>      struct domain *cd = current->domain;
>      char c = *val;
>  
> -    BUG_ON(bytes != 1);
> +    ASSERT(bytes == 1 || port == 0xe9);
>  
> -    /* Accept only printable characters, newline, and horizontal tab. */
> -    if ( !isprint(c) && (c != '\n') && (c != '\t') )
> +    /*
> +     * Ignore any input requests and accept only printable characters,
> +     * newline, and horizontal tab.
> +     */
> +    if ( dir != IOREQ_WRITE ||
> +         (!isprint(c) && (c != '\n') && (c != '\t')) )
>          return X86EMUL_OKAY;

Given that there is no functionality on the read side, it should be
explicitly terminated with ~0 rather than ignored.

Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

~Andrew

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