From: sernkut <sernkut@users.noreply.github.com>
To: ml@inbox.vuxu.org
Subject: [ISSUE] qemu/libvirt: virt-aa-helper refuses to create AppArmor VM profiles when using QEMU provided OVMF images from /usr/share/qemu
Date: Wed, 18 Aug 2021 16:38:11 +0200 [thread overview]
Message-ID: <gh-mailinglist-notifications-41a7ca26-5023-4802-975b-f1789d68868e-void-packages-32562@inbox.vuxu.org> (raw)
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New issue by sernkut on void-packages repository
https://github.com/void-linux/void-packages/issues/32562
Description:
# qemu/libvirt: virt-aa-helper refuses to create AppArmor VM profiles when using QEMU provided OVMF images from /usr/share/qemu
This issue is related to #31904
### System
xuname:
- Void 5.13.10_1 x86_64-musl GenuineIntel uptodate rrnFFF
Packages:
- qemu-6.0.0_3, libvirt-7.6.0_1
### Expected behavior
When using AppArmor, a VM that is using the QEMU provided UEFI OVMF images should start normally.
### Actual behavior
When trying to start a VM using the default QEMU provided OVMF UEFI firmware images while AppArmor is setup and running. VM startup fails with `internal error: cannot load AppArmor profile libvirt-{VM-UUID}`.
### Cause
The QEMU provided OVMF UEFI firmware image files are under `/usr/share/qemu/*.fd` and this works fine if you are not using AppArmor.
But when AppArmor is enabled, libvirtd automatically tries to generate a seperate AppArmor profile for each started VM using `virt-aa-helper`.
But when we look into the source code of `virt-aa-helper` ([`src/security/virt-aa-helper.c:454-490:valid_path()`](https://github.com/libvirt/libvirt/blob/master/src/security/virt-aa-helper.c#L454-L490)) we see that there are multiple restricted file paths that will not be added to the AppArmor profile in any circumstance.
Here's the aforementioned snippet from the `virt-aa-helper` sources:
```
const char * const restricted[] = {
"/bin/",
"/etc/",
"/lib",
"/lost+found/",
"/proc/",
"/sbin/",
"/selinux/",
"/sys/",
"/usr/bin/",
"/usr/lib",
"/usr/sbin/",
"/usr/share/",
"/usr/local/bin/",
"/usr/local/etc/",
"/usr/local/lib",
"/usr/local/sbin/"
};
/* these paths are ok for readonly, but not read/write */
const char * const restricted_rw[] = {
"/boot/",
"/vmlinuz",
"/initrd",
"/initrd.img",
"/usr/share/edk2/",
"/usr/share/OVMF/", /* for OVMF images */
"/usr/share/ovmf/", /* for OVMF images */
"/usr/share/AAVMF/", /* for AAVMF images */
"/usr/share/qemu-efi/", /* for AAVMF images */
"/usr/share/qemu-efi-aarch64/" /* for AAVMF images */
};
/* override the above with these */
const char * const override[] = {
"/sys/devices/pci", /* for hostdev pci devices */
"/sys/kernel/config/target/vhost", /* for hostdev vhost_scsi devices */
"/etc/libvirt-sandbox/services/" /* for virt-sandbox service config */
};
```
From the snippet above you can see that `/usr/share/` is restricted, so its not allowed to be referenced in autogenerated AppArmor profiles by `virt-aa-helper`. There are allowed paths under `/usr/share` which are listed in `restricted_rw`.
But because the files are under `/usr/share/qemu` when `virt-aa-helper` tries to generate the VM AppArmor profile and if it stumbles across the path `/usr/share/qemu/edk2-x86_64-code.fd` it checks and realizes that the path is in `restricted`, but not in `restricted_rw` and so it skips this file. But then `virt-aa-helper` also [checks and realizes](https://github.com/libvirt/libvirt/blob/master/src/security/virt-aa-helper.c#L1441-L1442) that the generated VM definition is invalid without the UEFI firmware image path, so it errors out completly and doesn't write any AppArmor profile.
### Possible Fixes
#### 1. Patch virt-aa-helper's `restricted_rw` to include `/usr/share/qemu`
This would work, but might introduce security issues.
#### 2. Move files from `/usr/share/qemu` to `/usr/share/ovmf` or `/usr/share/edk2`
NOTE: These are the instructions for the x86_64 non secure boot OVMF image, but it's basically the same for the other images.
First check the files we need to copy from `/usr/share/qemu/firmware/60-edk2-x86_64.json` and look for the executable and nvram-template filepaths.
Then copy the required OVMF firmware files to the `/usr/share/ovmf` directory:
```
mkdir /usr/share/ovmf
cp /usr/share/qemu/{edk2-i386-vars.fd,edk2-x86_64-code.fd} /usr/share/ovmf
```
Lastly you need the copy the file from the first step and rename it to eg. `60-edk2-x86_64-custom.json` and then update the paths in that copy to the files in `/usr/share/ovmf`.
(The files in `/usr/share/qemu/firmware/` are used by virt-manager when searching for UEFI firmware images)
### Conclusion
The safest fix probably would be fix no. 2.
On Arch, you can use the OVMF UEFI images by just installing the `ovmf` package which places the files in the correct place (firmware in `/usr/share/ovmf` and definitions used by virt-manager in `/usr/share/qemu/firmware/`). Also Arch doesn't provide any UEFI firmware in the `qemu` package.
So a seperate UEFI firmware package is also an option.
<font size="2">(Sorry for any grammar/spelling mistakes as english isn't my native language. This is also my first ever issue to anything anywhere so sorry if i did something wrong)</font>
next reply other threads:[~2021-08-18 14:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 14:38 sernkut [this message]
2021-08-18 22:20 ` paper42
2021-08-18 22:39 ` sernkut
2021-08-18 22:39 ` [ISSUE] [CLOSED] " sernkut
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