Re: [Xen-devel] [PATCH] x86/VMX: sanitize VM86 TSS handling

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.02.17 at 14:19, <JBeulich@xxxxxxxx> wrote:
> --- a/tools/firmware/hvmloader/hvmloader.c
> +++ b/tools/firmware/hvmloader/hvmloader.c
> @@ -177,18 +177,30 @@ static void cmos_write_memory_size(void)
>  }
>  
>  /*
> - * Set up an empty TSS area for virtual 8086 mode to use. 
> - * The only important thing is that it musn't have any bits set 
> - * in the interrupt redirection bitmap, so all zeros will do.
> + * Set up an empty TSS area for virtual 8086 mode to use. Its content is
> + * going to be managed by Xen, but zero fill it just in case.
>   */
>  static void init_vm86_tss(void)
>  {
> +/*
> + * Have the TSS cover the ISA port range, which makes it
> + * - 104 bytes base structure
> + * - 32 bytes interrupt redirection bitmap
> + * - 128 bytes I/O bitmap
> + * - one trailing byte
> + * or a total of to 265 bytes. As it needs to be be a power of two for
> + * now (or else the alignment parameter to mem_alloc() needs adjustment),
> + * this ends up requiring 512 bytes.
> + */
> +#define TSS_SIZE 512
>      void *tss;
>  
> -    tss = mem_alloc(128, 128);
> -    memset(tss, 0, 128);
> +    tss = mem_alloc(TSS_SIZE, TSS_SIZE);

    tss = mem_alloc(TSS_SIZE, 128);

is sufficient here, as I've noticed (only) while reviewing Roger's
series v4 of which did trigger the creation of this patch. I've made
the change locally for now.

Jan


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