[edk2-devel] QEMU / OVMF ESP corruption

[Fred Lotter <fred.lotter@canonical.com>]

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Hi,

I would like to ask for help on a particular failure I am observing.

I have this boot flow:

OVMF -> bootx64.efi (GRUB) ---chainloads--> vmlinux.efi

1. Grub updates a variable grub.env in the EFI partition (sector 7283/7284)

virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 7283
nsectors 1
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 7284
nsectors 1
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
save_env --file (hd0,gpt2)/EFI/foo/grub.env BOOT

2. The vmlinux EFI stub results in a write area which includes the grub env
block

virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 4097
nsectors 1
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 4128
nsectors 64
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 5704
nsectors 64
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 7280
nsectors 128  ## <====
virtio_blk_rw_complete vdev 0x5e72efe06150 req 0x5e72ef435910 ret 0
virtio_blk_req_complete vdev 0x5e72efe06150 req 0x5e72ef435910 status 0
virtio_blk_handle_write vdev 0x5e72efe06150 req 0x5e72ef435910 sector 8304
nsectors 128

The end result of this is that the grub.env file is reset to its original
value, with the change written by grub reverted.

This pattern seen during the EFI stub preamble is also seen during OVMF
startup, so it seems this is some common EFI VAR ? related code. At OVMF
startup this seems to repeat a number of times before Grub starts.

===> If I move OVMF to pflash disks for code + vars, this issue does not
happen.

DETAILS:

I am using Ubuntu Noble (24.04) packages for the test environment.

QEMU:
----

qemu-system-x86_64 \
    -trace "virtio_blk*" \
    -accel kvm \
    -bios /usr/share/ovmf/OVMF.fd \
    -drive format=raw,file=disk.img,if=virtio \
    -device virtio-rng-pci \
    -netdev user,id=net0,hostfwd=tcp::8888-:8888 \
    -device virtio-net-pci,netdev=net0 \
    -m 1G \
    -serial mon:stdio \
    -nodefaults \
    -nographic

DISK:
-----

fdisk -l disk.img
Disk disk.img: 600 MiB, 629145600 bytes, 1228800 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 8984DCD3-7190-1246-A4BB-980CEE0EB65A

Device                                     Start     End Sectors  Size Type
disk.img1    2048    4095    2048    1M BIOS boot
disk.img2    4096  208895  204800  100M EFI System             ## EFI
PARTITION
disk.img3  208896  618495  409600  200M Microsoft basic data   ## BOOT
PARTITION
disk.img4  618496 1028095  409600  200M Microsoft basic data
disk.img5 1028096 1030143    2048    1M Linux filesystem
disk.img6 1030144 1228766  198623   97M Linux filesystem

EFI PARTITION:
--------------

.:
total 22
drwxr-xr-x 3 root    root      512 Jan  1  1970 ./
drwxrwxr-x 5 flotter flotter    13 Sep 26 11:30 ../
drwxr-xr-x 4 root    root      512 Sep 25 22:02 EFI/
-rwxr-xr-x 1 root    root    11375 Sep 26 11:01 NvVars*

./EFI:
total 2
drwxr-xr-x 4 root root 512 Sep 25 22:02 ./
drwxr-xr-x 3 root root 512 Jan  1  1970 ../
drwxr-xr-x 2 root root 512 Sep 25 22:02 boot/
drwxr-xr-x 2 root root 512 Sep 25 22:02 foo/

./EFI/boot:
total 557
drwxr-xr-x 2 root root    512 Sep 25 22:02 ./
drwxr-xr-x 4 root root    512 Sep 25 22:02 ../
-rwxr-xr-x 1 root root 569344 Sep 25 22:02 bootx64.efi*

./EFI/foo:
total 6
drwxr-xr-x 2 root root  512 Sep 25 22:02 ./
drwxr-xr-x 4 root root  512 Sep 25 22:02 ../
-rwxr-xr-x 1 root root 3151 Sep 25 22:02 grub.cfg*
-rwxr-xr-x 1 root root 1024 Sep 25 22:02 grub.env*

BOOT PARTITION:
--------------

vmlinux.efi  ## EFI STUB binary (Linux + initramfs)

Kind Regards,
Fred Lotter


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