From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH] tools/libxc: Don't leave scratch_pfn
 uninitialised if the domain has no memory
Date: Thu, 29 Jan 2015 18:35:52 +0000
Message-ID: <54CA7D88.5050702@linaro.org>
References: <1422460355-16163-1-git-send-email-andrew.cooper3@citrix.com>
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To: Andrew Cooper <andrew.cooper3@citrix.com>, Xen-devel <xen-devel@lists.xen.org>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>, Jan Beulich <JBeulich@suse.com>
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Hi Andrew,

On 28/01/15 15:52, Andrew Cooper wrote:
> c/s 5b5c40c0d1 "libxc: introduce a per architecture scratch pfn for temporary
> grant mapping" accidentally an issue whereby there were two paths out of
> xc_core_arch_get_scratch_gpfn() which returned 0, but only one of which
> assigned a value to the gpfn parameter.
> xc_domain_maximum_gpfn() can validly return 0, at which point gpfn 1 is a
> valid scratch page to use.

The original version was considering rc = 0 as an error. Should not we
keep the same behavior?

Regards,

> In addition, widen rc before adding 1 and possibly overflowing.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Julien Grall <julien.grall@linaro.org>
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Ian Campbell <Ian.Campbell@citrix.com>
> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> ---
>  tools/libxc/xc_core_x86.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxc/xc_core_x86.c b/tools/libxc/xc_core_x86.c
> index fac99ec..d8846f1 100644
> --- a/tools/libxc/xc_core_x86.c
> +++ b/tools/libxc/xc_core_x86.c
> @@ -214,10 +214,10 @@ xc_core_arch_get_scratch_gpfn(xc_interface *xch, domid_t domid,
>  
>      rc = xc_domain_maximum_gpfn(xch, domid);
>  
> -    if ( rc <= 0 )
> +    if ( rc < 0 )
>          return rc;
>  
> -    *gpfn = rc + 1;
> +    *gpfn = (xen_pfn_t)rc + 1;
>  
>      return 0;
>  }
> 


-- 
Julien Grall