Re: [Xen-devel] [PATCH v7 for-4.9 2/5] hvm/dmop: Make copy_buf_{from, to}_guest for a buffer not big enough an error.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: jennifer.herbert@xxxxxxxxxx [mailto:jennifer.herbert@xxxxxxxxxx]
> Sent: 21 April 2017 14:16
> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> Cc: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>; Jennifer Herbert
> <jennifer.herbert@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>;
> Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
> <JBeulich@xxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>
> Subject: [PATCH v7 for-4.9 2/5] hvm/dmop: Make copy_buf_{from,
> to}_guest for a buffer not big enough an error.
> 
> From: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
> 
> This makes copying to or from a buf that isn't big enough an error.
> If the buffer isnt big enough, trying to carry on regardless
> can only cause trouble later on.
> 
> Signed-off-by: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
> --
> CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> ---
> This patch takes the behaviour change part of patch the previouse
> [patch 2/4].
> ---
>  xen/arch/x86/hvm/dm.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
> index e583e41..63aa46c 100644
> --- a/xen/arch/x86/hvm/dm.c
> +++ b/xen/arch/x86/hvm/dm.c
> @@ -36,30 +36,32 @@ static bool copy_buf_from_guest(const
> xen_dm_op_buf_t bufs[],
>                                  unsigned int nr_bufs, void *dst,
>                                  unsigned int idx, size_t dst_size)
>  {
> -    size_t size;
> +    size_t buf_bytes;
> 
>      if ( idx >= nr_bufs )
>          return false;
> 
> -    memset(dst, 0, dst_size);
> -
> -    size = min_t(size_t, dst_size, bufs[idx].size);
> +    buf_bytes = bufs[idx].size;
> +    if ( dst_size > buf_bytes )
> +        return false;
> 
> -    return !copy_from_guest(dst, bufs[idx].h, size);
> +    return !copy_from_guest(dst, bufs[idx].h, buf_bytes);

What happens if dst_size < buf_bytes?

>  }
> 
>  static bool copy_buf_to_guest(const xen_dm_op_buf_t bufs[],
>                                unsigned int nr_bufs, unsigned int idx,
>                                const void *src, size_t src_size)
>  {
> -    size_t size;
> +    size_t buf_bytes;
> 
>      if ( idx >= nr_bufs )
>          return false;
> 
> -    size = min_t(size_t, bufs[idx].size, src_size);
> +    buf_bytes = bufs[idx].size;
> +    if ( src_size > buf_bytes )
> +        return false;
> 
> -    return !copy_to_guest(bufs[idx].h, src, size);
> +    return !copy_to_guest(bufs[idx].h, src, buf_bytes);

What happens if src_size < buf_bytes?

>  }
> 
>  static int track_dirty_vram(struct domain *d, xen_pfn_t first_pfn,
> --
> 2.1.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel