Bug 246413 - boot from 12.1 DVD iso as MBR causes panic zfree wild pointer
Summary: boot from 12.1 DVD iso as MBR causes panic zfree wild pointer
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: 12.1-RELEASE
Hardware: amd64 Any
: --- Affects Some People
Assignee: freebsd-bugs (Nobody)
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-05-12 04:11 UTC by John Millard
Modified: 2020-05-12 04:11 UTC (History)
0 users

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Description John Millard 2020-05-12 04:11:20 UTC 
This is related to 242106. My W520 lenovo thinkpad tries MBR boot before UEFI boot from DVD. Booting as MBR causes the panic. If I change the BIOS to try UEFI before MBR it works fine. The workaround for 242106 is to tell the VM to boot UEFI first.

The text of the panic is:

CD Loader 1.2

Building the boot loader arguments
Looking up /BOOT/LOADER... found
Relocating the loader and BTX
Starting the BTX loader

BTX loader 1.00 BTX version is 1.02
Consoles: internal video/keyboard
BIOS CD is cd0
BIOS drive C: is disk0
BIOS 630kb/3125884kb available memory

FreeBSD/x86 bootstrap loader, Revision 1.1
panic: zfree(90xbd69c6b0,8224): wild pointer
--> Press a key on the console to reboot <--

I reproduced this with disk and dvd ISO's

The code should probably sanity check the startup environment. This is not high priority as the work-around is easy. This bug will serve to document the problem and the work-around.