Re: [Xen-devel] [PATCH] x86/EDD: check MBR for BIOS magic before considering signature valid

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 30/05/2012 16:36, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/boot/edd.S
> +++ b/xen/arch/x86/boot/edd.S
> @@ -53,12 +53,16 @@ edd_mbr_sig_read:
>          jc      edd_mbr_sig_done                # on failure, we're done.
>          cmpb    $0, %ah                         # some BIOSes do not set CF
>          jne     edd_mbr_sig_done                # on failure, we're done.
> +        cmpw    $0xaa55, bootsym(boot_edd_info)+0x1fe
> +        jne     .Ledd_mbr_sig_next
>          movl    bootsym(boot_edd_info)+EDD_MBR_SIG_OFFSET,%eax
>          movb    %dl, (%bx)                      # store BIOS drive number
>          movl    %eax, 4(%bx)                    # store signature from MBR
>          incb    bootsym(boot_mbr_signature_nr)  # note that we stored
> something
> -        incb    %dl                             # increment to next device
>          addw    $8, %bx                         # increment sig buffer ptr
> +.Ledd_mbr_sig_next:
> +        incb    %dl                             # increment to next device
> +        jz      edd_mbr_sig_done
>          cmpb    $EDD_MBR_SIG_MAX,bootsym(boot_mbr_signature_nr)
>          jb      edd_mbr_sig_read
>  edd_mbr_sig_done:
> 
> 
> 
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