Support readonly feature of VirtIO block device

[ChinYikMing]

Why?

Enhances the security of the VirtIO block device by preventing unintended data corruption in the guest OS when accessing critical data.

Test

1. Clone the repo:

$ git clone https://github.com/ChinYikMing/rv32emu.git -b virtio-blk-readonly --depth 1 && cd rv32emu

2. Get the prebuilt images and build:

$ make ENABLE_SYSTEM=1 INITRD_SIZE=32 -j100 && make ENABLE_SYSTEM=1 artifact

3. Prepare disk image:

macOS:

# Might need to install file system utility
$ brew install e2fsprogs

# Create a disk image
$ dd if=/dev/zero of=disk.img bs=4M count=32
$ $(brew --prefix e2fsprogs)/sbin/mkfs.ext4 disk.img

Linux

# Create a disk image
$ dd if=/dev/zero of=disk.img bs=4M count=32
$ mkfs.ext4 disk.img

4. Check the kernel boot log which should have something as the following:

$ build/rv32emu -k build/linux-image/Image -i build/linux-image/rootfs.cpio -x vblk:disk.img,readonly

Might see something similar:

...
...
[    0.583109] virtio_blk virtio0: 1/0/0 default/read/poll queues
[    0.584873] virtio_blk virtio0: [vda] 262144 512-byte logical blocks (134 MB/128 MiB)
...
...

5. Mount the virtio block device:

# mkdir mnt
# mount /dev/vda mnt

Might see something similar:

[   37.134323] /dev/vda: Can't open blockdev
[   37.135211] /dev/vda: Can't open blockdev
[   37.136593] EXT4-fs (vda): INFO: recovery required on readonly filesystem
[   37.136804] EXT4-fs (vda): write access unavailable, cannot proceed (try mounting with noload)
mount: mounting /dev/vda on mnt failed: Read-only file system

For ext4 image, to maintain the consistency of the file system, the ext4 does the journal replay (which is failed by this error log: "recovery required on readonly filesystem) and mount command default use read and write permission. Thus, it has to mount with noload option.

6. Remount the virtio block device and manipulate the device:

# mount -o noload /dev/vda mnt

Try to create a file which should fail on readonly mounted device:

# touch mnt/apple
touch: mnt/apple: Read-only file system

Summary by Bito

This pull request introduces a readonly feature for the VirtIO block device, enhancing security by preventing unintended data corruption. Key changes include a readonly flag during initialization, updated function signatures, and improved command line options for usability.

Unit tests added: False

Estimated effort to review (1-5, lower is better): 2

[jserv]

Benchmarks

Benchmark suite	Current: c9e2b5f	Previous: b26e7fc	Ratio
Dhrystone	1274 Average DMIPS over 10 runs	1311 Average DMIPS over 10 runs	1.03
Coremark	913.979 Average iterations/sec over 10 runs	920.165 Average iterations/sec over 10 runs	1.01

This comment was automatically generated by workflow using github-action-benchmark.

[jserv]

I would like to ask @otteryc for reviewing.

[jserv]

Replace sizeof(char *[MAX_OPTS]) with ARRAY_SIZE.

[ChinYikMing]

Replace sizeof(char *[MAX_OPTS]) with ARRAY_SIZE.

ARRAY_SIZE gets the element count in an array but it does not know the size of each element. To use it, it should be used like this: ARRAY_SIZE(vblk_opts) * sizeof(vblk_opts[0]).

Thus, for more shorter, I would go with "partial Initialization" which would initialize the rest of the element to 0 by declaring the vblk_opts as char *vblk_opts[MAX_OPTS] = {NULL}.

[otteryc]

Looks good to me!
Please consider:

1. Refine the corresponding statements in README.md for clarity.
2. Fix the device_features_sel error also in semu as well.

[jserv]

Thank @ChinYikMing for contributing!