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[core] fix MBR protective message overwriting the primary GPT

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* We distractedly chose to populate the message from our protective MBR
  for GPT/UEFI-only boot media into the 4KB that directly followed the
  MBR, which of course is space that is being used by the primary GPT.
* This resulted on systems having to fall back to using the secondary
  GPT, which not all appear to be designed to do.
* Alter the code to ensure the protective message is written at LBA 34,
  after the primary GPT.
* Closes #1507
This commit is contained in:
Pete Batard 2020-04-13 17:05:33 +01:00
parent 129aa64394
commit 2dd538b7cb
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GPG key ID: 38E0CF5E69EDD671
9 changed files with 60 additions and 57 deletions
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21
src/format.c
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@ -906,7 +906,7 @@ out:
static BOOL WriteSBR(HANDLE hPhysicalDrive)
{
// TODO: Do we need anything special for 4K sectors?
DWORD size, max_size, mbr_size = 0x200;
DWORD size, max_size, br_size = 0x200;
int r, sub_type = boot_type;
unsigned char* buf = NULL;
FAKE_FD fake_fd = { 0 };
@ -914,10 +914,6 @@ static BOOL WriteSBR(HANDLE hPhysicalDrive)
fake_fd._handle = (char*)hPhysicalDrive;
set_bytes_per_sector(SelectedDrive.SectorSize);
// Ensure that we have sufficient space for the SBR
max_size = IsChecked(IDC_OLD_BIOS_FIXES) ?
(DWORD)(SelectedDrive.SectorsPerTrack * SelectedDrive.SectorSize) : 1 * MB;
max_size -= mbr_size;
// Syslinux has precedence over Grub
if ((boot_type == BT_IMAGE) && (!HAS_SYSLINUX(img_report))) {
if (img_report.has_grub4dos)
@ -932,12 +928,12 @@ static BOOL WriteSBR(HANDLE hPhysicalDrive)
case BT_GRUB4DOS:
uprintf("Writing Grub4Dos SBR");
buf = GetResource(hMainInstance, MAKEINTRESOURCEA(IDR_GR_GRUB_GRLDR_MBR), _RT_RCDATA, "grldr.mbr", &size, FALSE);
if ((buf == NULL) || (size <= mbr_size)) {
if ((buf == NULL) || (size <= br_size)) {
uprintf("grldr.mbr is either not present or too small");
return FALSE;
}
buf = &buf[mbr_size];
size -= mbr_size;
buf = &buf[br_size];
size -= br_size;
break;
case BT_GRUB2:
if (grub2_buf != NULL) {
@ -957,6 +953,7 @@ static BOOL WriteSBR(HANDLE hPhysicalDrive)
case BT_NON_BOOTABLE:
uprintf("Writing protective message SBR");
size = 4 * KB;
br_size = 17 * KB; // 34 sectors are reserved for protective MBR + primary GPT
buf = GetResource(hMainInstance, MAKEINTRESOURCEA(IDR_SBR_MSG), _RT_RCDATA, "msg.txt", &size, TRUE);
if (buf == NULL) {
uprintf("Could not access message");
@ -968,11 +965,15 @@ static BOOL WriteSBR(HANDLE hPhysicalDrive)
return TRUE;
}
if (size > max_size) {
// Ensure that we have sufficient space for the SBR
max_size = IsChecked(IDC_OLD_BIOS_FIXES) ?
(DWORD)(SelectedDrive.SectorsPerTrack * SelectedDrive.SectorSize) : 1 * MB;
if (br_size + size > max_size) {
uprintf(" SBR size is too large - You may need to uncheck 'Add fixes for old BIOSes'.");
return FALSE;
}
r = write_data(fp, mbr_size, buf, (uint64_t)size);
r = write_data(fp, br_size, buf, (uint64_t)size);
safe_free(grub2_buf);
if (sub_type == BT_NON_BOOTABLE)
safe_free(buf);