Messages in this thread | | | Date | Fri, 8 Dec 2023 00:54:18 +0100 | Subject | Re: [PATCH v2] initramfs: Expose retained initrd as sysfs file | From | Alexander Graf <> |
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Hi Bagas,
On 07.12.23 13:37, Bagas Sanjaya wrote: > 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@amazon.com> >> +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.
Thanks a bunch for testing the patch!
The reason you're seeing microcode is that something in your boot chain (grub maybe? sd-boot?) sends multiple initrd blobs to Linux: One that contains microcode and another that contains the real initrd. Linux continues extracting past the first cpio archive.
Alex
Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
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