[PATCH][RFC] Add boot sector checksums to EDD

From: Carl-Daniel Hailfinger
Date: Tue Nov 09 2004 - 23:44:35 EST


Hi Matt,

this first draft of a patch to implement boot sector checksums in EDD.
Since the comments in edd.S and edd.h discourage changing some offsets,
I made my code overwrite the /sys/firmware/edd/int13_dev*/mbr_signature
file contents. For a later patch I would suggest to add a mbr_checksum
file, so the two can coexist.
The patch is tested and didn't break anything on my machine so far.
Please comment.

Regards,
Carl-Daniel
http://www.hailfinger.org/

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.kernel.2004@xxxxxxx>

--- ./linux-2.6.9/arch/i386/boot/edd.S~ 2004-11-05 14:27:08.000000000 +0100
+++ ./linux-2.6.9/arch/i386/boot/edd.S 2004-11-06 23:55:23.000000000 +0100
@@ -5,7 +5,9 @@
* projects 1572D, 1484D, 1386D, 1226DT
* disk signature read by Matt Domsch <Matt_Domsch@xxxxxxxx>
* and Andrew Wilks <Andrew_Wilks@xxxxxxxx> September 2003, June 2004
- * legacy CHS retreival by Patrick J. LoPresti <patl@xxxxxxxxxxxxxxxxxxxxx>
+ * disk checksum computation by Carl-Daniel Hailfinger
+ * <c-d.hailfinger.kernel.2004@xxxxxxx> November 2004
+ * legacy CHS retrieval by Patrick J. LoPresti <patl@xxxxxxxxxxxxxxxxxxxxx>
* March 2004
* Use EXTENDED READ calls if possible, Matt Domsch, October 2004
*/
@@ -88,10 +90,21 @@
movb %dl, %bl # copy drive number to ebx
sub $0x80, %bl # subtract 80h from drive number
shlw $2, %bx # multiply by 4
+ movw %bx, %cx # save bx
addw $EDD_MBR_SIG_BUF, %bx # add to sig_buf
# bx now points to the right sig slot
movl (EDDBUF+EDD_MBR_SIG_OFFSET), %eax # read sig out of the MBR
movl %eax, (%bx) # store success
+ movw %cx, %bx # restore bx
+ addw $EDD_MBR_CKSUM_BUF, %bx # add to cksum_buf
+ # bx now points to the right cksum slot
+ xorl %eax, %eax # clear eax
+ movl $0x7f, %ecx # loop counter
+edd_mbr_compute_checksum:
+ xorl EDDBUF(,%ecx,4), %eax # compute checksum of mbr
+ decl %ecx
+ jns edd_mbr_compute_checksum # until the checksum in complete
+ movl %eax, (%bx) # store success
incb (EDD_MBR_SIG_NR_BUF) # note that we stored something
edd_mbr_sig_next:
incb %dl # increment to next device
--- ./linux-2.6.9/include/linux/edd.h~ 2004-11-05 14:27:47.000000000 +0100
+++ ./linux-2.6.9/include/linux/edd.h 2004-11-06 23:43:20.000000000 +0100
@@ -50,6 +50,7 @@
#define EDD_MBR_SIG_OFFSET 0x1B8 /* offset of signature in the MBR */
#define EDD_DEV_ADDR_PACKET_LEN 0x10 /* for int13 fn42 */
#define EDD_MBR_SIG_BUF 0x290 /* addr in boot params */
+#define EDD_MBR_CKSUM_BUF 0x290 /* addr in boot params */
#define EDD_MBR_SIG_MAX 16 /* max number of signatures to store */
#define EDD_MBR_SIG_NR_BUF 0x1ea /* addr of number of MBR signtaures at EDD_MBR_SIG_BUF
in boot_params - treat this as 1 byte */
-
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