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initramfs: Expose retained initrd as sysfs file
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. With this patch applied, there is a new /sys/firmware/initrd file when the kernel was booted with an initrd and "retain_initrd" command line option is set. Signed-off-by: Alexander Graf <graf@amazon.com> Tested-by: Bagas Sanjaya <bagasdotme@gmail.com> Link: https://lore.kernel.org/r/20231207235654.16622-1-graf@amazon.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Documentation/ABI/testing/sysfs-firmware-initrd
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8
Documentation/ABI/testing/sysfs-firmware-initrd
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@ -0,0 +1,8 @@
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What: /sys/firmware/initrd
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Date: December 2023
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Contact: Alexander Graf <graf@amazon.com>
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Description:
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When the kernel was booted with an initrd and the
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"retain_initrd" option is set on the kernel command
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line, /sys/firmware/initrd contains the contents of the
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initrd that the kernel was booted with.
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@ -2438,7 +2438,7 @@
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between unregistering the boot console and initializing
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between unregistering the boot console and initializing
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the real console.
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the real console.
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keepinitrd [HW,ARM]
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keepinitrd [HW,ARM] See retain_initrd.
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kernelcore= [KNL,X86,IA-64,PPC]
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kernelcore= [KNL,X86,IA-64,PPC]
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Format: nn[KMGTPE] | nn% | "mirror"
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Format: nn[KMGTPE] | nn% | "mirror"
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@ -5580,7 +5580,8 @@
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Useful for devices that are detected asynchronously
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Useful for devices that are detected asynchronously
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(e.g. USB and MMC devices).
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(e.g. USB and MMC devices).
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retain_initrd [RAM] Keep initrd memory after extraction
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retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
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be accessible via /sys/firmware/initrd.
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retbleed= [X86] Control mitigation of RETBleed (Arbitrary
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retbleed= [X86] Control mitigation of RETBleed (Arbitrary
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Speculative Code Execution with Return Instructions)
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Speculative Code Execution with Return Instructions)
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@ -574,6 +574,16 @@ extern unsigned long __initramfs_size;
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#include <linux/initrd.h>
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#include <linux/initrd.h>
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#include <linux/kexec.h>
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#include <linux/kexec.h>
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static ssize_t raw_read(struct file *file, struct kobject *kobj,
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struct bin_attribute *attr, char *buf,
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loff_t pos, size_t count)
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{
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memcpy(buf, attr->private + pos, count);
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return count;
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}
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static BIN_ATTR(initrd, 0440, raw_read, NULL, 0);
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void __init reserve_initrd_mem(void)
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void __init reserve_initrd_mem(void)
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{
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{
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phys_addr_t start;
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phys_addr_t start;
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@ -715,8 +725,14 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
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* If the initrd region is overlapped with crashkernel reserved region,
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* If the initrd region is overlapped with crashkernel reserved region,
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* free only memory that is not part of crashkernel region.
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* free only memory that is not part of crashkernel region.
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*/
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*/
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if (!do_retain_initrd && initrd_start && !kexec_free_initrd())
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if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) {
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free_initrd_mem(initrd_start, initrd_end);
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free_initrd_mem(initrd_start, initrd_end);
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} else if (do_retain_initrd && initrd_start) {
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bin_attr_initrd.size = initrd_end - initrd_start;
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bin_attr_initrd.private = (void *)initrd_start;
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if (sysfs_create_bin_file(firmware_kobj, &bin_attr_initrd))
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pr_err("Failed to create initrd sysfs file");
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}
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initrd_start = 0;
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initrd_start = 0;
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initrd_end = 0;
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initrd_end = 0;
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