Re: [Xen-devel] [PATCH 1/7] libxc: fix uninitialized variable in xc_cpuid_pv_policy()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/07/15 18:37, Jennifer Herbert wrote:
> If xc_domain_get_guest_width were to fail, guest_width is not set, and
> hence guest_64bit becomes undefined.
> Fix is to initialise to 0, and report error if call fails.
>
> Signed-off-by: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
> ---
>  tools/libxc/xc_cpuid_x86.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
> index c97f91a..847b701 100644
> --- a/tools/libxc/xc_cpuid_x86.c
> +++ b/tools/libxc/xc_cpuid_x86.c
> @@ -437,14 +437,16 @@ static void xc_cpuid_pv_policy(

Urgh - let another libxc function which can fail hard in several ways,
yet is void.

>  {
>      DECLARE_DOMCTL;
>      unsigned int guest_width;
> -    int guest_64bit;
> +    int guest_64bit = 0;

The default in Xen is that a PV guest is 64bit until explicitly
converted to being compat.  The better default therefore is 1.

>      char brand[13];
>      uint64_t xfeature_mask;
>  
>      xc_cpuid_brand_get(brand);
>  
> -    xc_domain_get_guest_width(xch, domid, &guest_width);
> -    guest_64bit = (guest_width == 8);
> +    if (xc_domain_get_guest_width(xch, domid, &guest_width) == 0)
> +        guest_64bit = (guest_width == 8);
> +    else
> +        ERROR("Could not read guest word width.");

No full stop please.

>  
>      /* Detecting Xen's atitude towards XSAVE */
>      memset(&domctl, 0, sizeof(domctl));


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