[Patch] Fixed BIOS int 13h, ah=48h

[jlxip]

Patch for VirtualBox 6.1.8. Fixes an impossible condition in «edd_fill_dpt» function, which implements the function 48h of the BIOS interrupt 13h.

diff -ruN ./VirtualBox-6.1.8{.orig,}/src/VBox/Devices/PC/BIOS/disk.c
--- ./VirtualBox-6.1.8.orig/src/VBox/Devices/PC/BIOS/disk.c	2020-05-14 20:39:11.000000000 +0200
+++ ./VirtualBox-6.1.8/src/VBox/Devices/PC/BIOS/disk.c	2020-05-21 14:53:18.672394097 +0200
@@ -140,6 +140,7 @@
 int edd_fill_dpt(dpt_t __far *dpt, bio_dsk_t __far *bios_dsk, uint8_t device)
 {
     uint16_t    ebda_seg = read_word(0x0040,0x000E);
+    uint16_t    new_dpt_size;
 
     /* Check if buffer is large enough. */
     if (dpt->size < 0x1a)
@@ -149,7 +150,7 @@
     if (dpt->size >= 0x1a) {
         uint64_t    lba;
 
-        dpt->size      = 0x1a;
+        new_dpt_size   = 0x1a;
         dpt->blksize   = bios_dsk->devices[device].blksize;
 
         if (bios_dsk->devices[device].device == DSK_DEVICE_CDROM) {
@@ -175,7 +176,7 @@
         uint8_t     channel, irq, mode, checksum, i, xlation;
         uint16_t    iobase1, iobase2, options;
 
-        dpt->size = 0x1e;
+        new_dpt_size      = 0x1e;
         dpt->dpte_segment = ebda_seg;
         dpt->dpte_offset  = (uint16_t)&EbdaData->bdisk.dpte;
 
@@ -227,7 +228,7 @@
         iface   = bios_dsk->channels[channel].iface;
         iobase1 = bios_dsk->channels[channel].iobase1;
 
-        dpt->size       = 0x42;
+        new_dpt_size    = 0x42;
         dpt->key        = 0xbedd;
         dpt->dpi_length = 0x24;
         dpt->reserved1  = 0;
@@ -269,6 +270,8 @@
         checksum = -checksum;
         dpt->checksum = checksum;
     }
+
+    dpt->size = new_dpt_size;
     return 0;
 }
 

[jlxip]

Patch file