[Xen-changelog] [xen-4.1-testing] x86/EDD: check MBR for BIOS magic before considering signature valid

[Xen patchbot-4.1-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <JBeulich@xxxxxxxx>
# Date 1346762742 -7200
# Node ID 3fe75068fa354d347029d20210d49c765babedac
# Parent  060fbf05ce532d86314bd9db96fe9510495abed3
x86/EDD: check MBR for BIOS magic before considering signature valid

Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
xen-unstable changeset: 25431:cdced279e792
xen-unstable date: Thu May 31 08:18:13 UTC 2012
---


diff -r 060fbf05ce53 -r 3fe75068fa35 xen/arch/x86/boot/edd.S
--- a/xen/arch/x86/boot/edd.S   Tue Sep 04 14:44:37 2012 +0200
+++ b/xen/arch/x86/boot/edd.S   Tue Sep 04 14:45:42 2012 +0200
@@ -61,12 +61,16 @@ 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
+        addw    $8, %bx                         # increment sig buffer ptr
+.Ledd_mbr_sig_next:
         incb    %dl                             # increment to next device
-        addw    $8, %bx                         # increment sig buffer ptr
+        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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