When the kernel command line option "retain_initrd" is set, we do not
free the initrd memory. However, we also don't expose it to anyone for
consumption. That leaves us in a weird situation where the only user of
this feature is ppc64 and arm64 specific kexec tooling.
To make it more generally useful, this patch adds a kobject to the
firmware object that contains the initrd context when "retain_initrd"
is set. That way, we can access the initrd any time after boot from
user space and for example hand it into kexec as --initrd parameter
if we want to reboot the same initrd. Or inspect it directly locally.
Signed-off-by: Alexander Graf <[email protected]>
---
.../admin-guide/kernel-parameters.txt | 5 +++--
init/initramfs.c | 18 +++++++++++++++++-
2 files changed, 20 insertions(+), 3 deletions(-)
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;
--
2.40.1
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
On 06.12.23 21:00, Andrew Morton wrote:
> On Wed, 6 Dec 2023 14:16:27 +0000 Alexander Graf <[email protected]> wrote:
>
>> When the kernel command line option "retain_initrd" is set, we do not
>> free the initrd memory. However, we also don't expose it to anyone for
>> consumption. That leaves us in a weird situation where the only user of
>> this feature is ppc64 and arm64 specific kexec tooling.
>>
>> To make it more generally useful, this patch adds a kobject to the
>> firmware object that contains the initrd context when "retain_initrd"
>> is set. That way, we can access the initrd any time after boot from
>> user space and for example hand it into kexec as --initrd parameter
>> if we want to reboot the same initrd. Or inspect it directly locally.
> I think it would be helpful if the changelog were mention and describe
> the new /sys/firmware/initrd. And I assume we should add a
> Documentation/ABI/testing/sysfs-firmware-initrd.
Thanks a bunch for the suggestions - let me send v2 with both addressed :)
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