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[hdprefix] Avoid attempts to read beyond the end of the disk 

When booting from a hard disk image (e.g. bin/ipxe.usb) within an
emulator such as QEMU, the disk may not exist beyond the end of the
image.  Limit all reads to the length of the image to avoid spurious
errors when loading the iPXE image.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
pull/64/head
Michael Brown 2017-06-13 13:16:26 +01:00
parent 1fdf4dddbd
commit 84e25513b1
1 changed files with 9 additions and 5 deletions
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14
src/arch/x86/prefix/hdprefix.S
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@ -27,14 +27,18 @@ load_image:
popw %es popw %es
popal popal
1: /* Read to end of current track */ 1: /* Read to end of current track (or end of image) */
movb %cl, %al movb %cl, %al
negb %al negb %al
addb max_sector, %al addb max_sector, %al
incb %al incb %al
andb $0x3f, %al andb $0x3f, %al
movzbl %al, %eax movzbl %al, %eax
call *read_sectors movl load_length, %ebx
cmpl %eax, %ebx
ja 2f
movl %ebx, %eax
2: call *read_sectors
jc load_failed jc load_failed
/* Update %es */ /* Update %es */
@ -53,12 +57,12 @@ load_image:
orb $0x01, %cl orb $0x01, %cl
incb %dh incb %dh
cmpb max_head, %dh cmpb max_head, %dh
jbe 2f jbe 3f
xorb %dh, %dh xorb %dh, %dh
incb %ch incb %ch
jnc 2f jnc 3f
addb $0xc0, %cl addb $0xc0, %cl
2: 3:
/* Loop until whole image is read */ /* Loop until whole image is read */
subl %eax, load_length subl %eax, load_length
ja 1b ja 1b