On Wed, Dec 06, 2023 at 09:33:23PM +0000, Alexander Graf wrote:
> diff --git a/Documentation/ABI/testing/sysfs-firmware-initrd b/Documentation/ABI/testing/sysfs-firmware-initrd
> new file mode 100644
> index 000000000000..20bf7cf77a19
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-initrd
> @@ -0,0 +1,8 @@
> +What: /sys/firmware/initrd
> +Date: December 2023
> +Contact: Alexander Graf <graf@xxxxxxxxxx>
> +Description:
> + When the kernel was booted with an initrd and the
> + "retain_initrd" option is set on the kernel command
> + line, /sys/firmware/initrd contains the contents of the
> + initrd that the kernel was booted with.
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 65731b060e3f..51575cd31741 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2438,7 +2438,7 @@
> between unregistering the boot console and initializing
> the real console.
>
> - keepinitrd [HW,ARM]
> + keepinitrd [HW,ARM] See retain_initrd.
>
> kernelcore= [KNL,X86,IA-64,PPC]
> Format: nn[KMGTPE] | nn% | "mirror"
> @@ -5580,7 +5580,8 @@
> Useful for devices that are detected asynchronously
> (e.g. USB and MMC devices).
>
> - retain_initrd [RAM] Keep initrd memory after extraction
> + retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
> + be accessible via /sys/firmware/initrd.
>
> retbleed= [X86] Control mitigation of RETBleed (Arbitrary
> Speculative Code Execution with Return Instructions)
> diff --git a/init/initramfs.c b/init/initramfs.c
> index 8d0fd946cdd2..25244e2a5739 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -574,6 +574,16 @@ extern unsigned long __initramfs_size;
> #include <linux/initrd.h>
> #include <linux/kexec.h>
>
> +static ssize_t raw_read(struct file *file, struct kobject *kobj,
> + struct bin_attribute *attr, char *buf,
> + loff_t pos, size_t count)
> +{
> + memcpy(buf, attr->private + pos, count);
> + return count;
> +}
> +
> +static BIN_ATTR(initrd, 0440, raw_read, NULL, 0);
> +
> void __init reserve_initrd_mem(void)
> {
> phys_addr_t start;
> @@ -715,8 +725,14 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
> * If the initrd region is overlapped with crashkernel reserved region,
> * free only memory that is not part of crashkernel region.
> */
> - if (!do_retain_initrd && initrd_start && !kexec_free_initrd())
> + if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) {
> free_initrd_mem(initrd_start, initrd_end);
> + } else if (do_retain_initrd) {
> + bin_attr_initrd.size = initrd_end - initrd_start;
> + bin_attr_initrd.private = (void *)initrd_start;
> + if (sysfs_create_bin_file(firmware_kobj, &bin_attr_initrd))
> + pr_err("Failed to create initrd sysfs file");
> + }
> initrd_start = 0;
> initrd_end = 0;
>
On my Arch Linux system, /sys/firmware/initrd is not same as initramfs image
from /boot partition that is uncompressed. `ls -l` listing shows
(with /tmp/initramfs-boot is unzstd'ed initramfs of the same kernel booted):
```
-r--r----- 1 root root 22967535 Dec 7 19:32 /sys/firmware/initrd
-rw------- 1 root root 40960000 Dec 7 19:26 /tmp/initramfs-boot
```
And thus, `cpio -i -v` listing differs. While in uncompressed initramfs,
I got expected initramfs contents (early userpace for booting), doing the same
to /sys/firmware/initrd only shows Intel microcode.
Regardless, exposing initramfs as advertised in the patch description works for
me.
Tested-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
Thanks.
--
An old man doll... just what I always wanted! - Clara
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