loader: fix multiboot loading on UEFI
ClosedPublic
Actions

Authored by royger on Aug 11 2021, 3:05 PM.

Details

Reviewers

kib
imp

Commits

rG5e4279a8f35a: loader: fix multiboot loading on UEFI

Summary

The Xen kernel has no symbols tables, so calling lookup_symbol against
it triggers the following Divide by Zero fault:

Loading Xen kernel...
/boot/xen data=0x2809c8+0x149638 |
!! X64 Exception Type - 00(#DE - Divide Error) CPU Apic ID - 00000000 !!

Fix lookup_symbol to prevent the #DE fault from happening if the
symbol table is not loaded and also fix loadfile_raw to mark multiboot
kernels as relocatable, since the only multiboot kernel supported is
Xen and was already unconditionally booted as relocatable.

Fixes: f75caed644a5 ('amd64 UEFI loader: stop copying staging area to 2M physical')

Diff Detail

Repository

rG FreeBSD src repository

Lint

Lint Not Applicable

Unit

Tests Not Applicable

Event Timeline

royger created this revision.Aug 11 2021, 3:05 PM

Herald added subscribers: dab, imp. · View Herald TranscriptAug 11 2021, 3:05 PM

royger requested review of this revision.Aug 11 2021, 3:05 PM

Harbormaster completed remote builds in B40997: Diff 93546.Aug 11 2021, 3:05 PM

imp accepted this revision.Aug 11 2021, 3:41 PM

This revision is now accepted and ready to land.Aug 11 2021, 3:41 PM

Note that 'relocatable' means variyng not VA, but PA. Loader still maps the kernel at KERNBASE.

In D31507#710357, @kib wrote:

Note that 'relocatable' means variyng not VA, but PA. Loader still maps the kernel at KERNBASE.

Right. In the Xen case the kernel is started in protected mode with paging disabled, so it's only relocatable in the PA space, because there's no page table provided at entry point.

Thanks for the reviews.

Closed by commit rG5e4279a8f35a: loader: fix multiboot loading on UEFI (authored by royger). · Explain WhyAug 12 2021, 7:24 AM

This revision was automatically updated to reflect the committed changes.

royger added a commit: rG5e4279a8f35a: loader: fix multiboot loading on UEFI.