From 84e25513b1ce6aeb4f0d6c9d20cd687c00591de8 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Tue, 13 Jun 2017 13:16:26 +0100 Subject: [PATCH] [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 --- src/arch/x86/prefix/hdprefix.S | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/src/arch/x86/prefix/hdprefix.S b/src/arch/x86/prefix/hdprefix.S index 24f5d385..28c8a532 100644 --- a/src/arch/x86/prefix/hdprefix.S +++ b/src/arch/x86/prefix/hdprefix.S @@ -27,14 +27,18 @@ load_image: popw %es popal -1: /* Read to end of current track */ +1: /* Read to end of current track (or end of image) */ movb %cl, %al negb %al addb max_sector, %al incb %al andb $0x3f, %al 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 /* Update %es */ @@ -53,12 +57,12 @@ load_image: orb $0x01, %cl incb %dh cmpb max_head, %dh - jbe 2f + jbe 3f xorb %dh, %dh incb %ch - jnc 2f + jnc 3f addb $0xc0, %cl -2: +3: /* Loop until whole image is read */ subl %eax, load_length ja 1b