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![Eric DeVolder](/assets/img/avatar_default.png)
The hotplug support for kexec_load() requires changes to the userspace kexec-tools and a little extra help from the kernel. Given a kdump capture kernel loaded via kexec_load(), and a subsequent hotplug event, the crash hotplug handler finds the elfcorehdr and rewrites it to reflect the hotplug change. That is the desired outcome, however, at kernel panic time, the purgatory integrity check fails (because the elfcorehdr changed), and the capture kernel does not boot and no vmcore is generated. Therefore, the userspace kexec-tools/kexec must indicate to the kernel that the elfcorehdr can be modified (because the kexec excluded the elfcorehdr from the digest, and sized the elfcorehdr memory buffer appropriately). To facilitate hotplug support with kexec_load(): - a new kexec flag KEXEC_UPATE_ELFCOREHDR indicates that it is safe for the kernel to modify the kexec_load()'d elfcorehdr - the /sys/kernel/crash_elfcorehdr_size node communicates the preferred size of the elfcorehdr memory buffer - The sysfs crash_hotplug nodes (ie. /sys/devices/system/[cpu|memory]/crash_hotplug) dynamically take into account kexec_file_load() vs kexec_load() and KEXEC_UPDATE_ELFCOREHDR. This is critical so that the udev rule processing of crash_hotplug is all that is needed to determine if the userspace unload-then-load of the kdump image is to be skipped, or not. The proposed udev rule change looks like: # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" The table below indicates the behavior of kexec_load()'d kdump image updates (with the new udev crash_hotplug rule in place): Kernel |Kexec -------+-----+---- Old |Old |New | a | a -------+-----+---- New | a | b -------+-----+---- where kexec 'old' and 'new' delineate kexec-tools has the needed modifications for the crash hotplug feature, and kernel 'old' and 'new' delineate the kernel supports this crash hotplug feature. Behavior 'a' indicates the unload-then-reload of the entire kdump image. For the kexec 'old' column, the unload-then-reload occurs due to the missing flag KEXEC_UPDATE_ELFCOREHDR. An 'old' kernel (with 'new' kexec) does not present the crash_hotplug sysfs node, which leads to the unload-then-reload of the kdump image. Behavior 'b' indicates the desired optimized behavior of the kernel directly modifying the elfcorehdr and avoiding the unload-then-reload of the kdump image. If the udev rule is not updated with crash_hotplug node check, then no matter any combination of kernel or kexec is new or old, the kdump image continues to be unload-then-reload on hotplug changes. To fully support crash hotplug feature, there needs to be a rollout of kernel, kexec-tools and udev rule changes. However, the order of the rollout of these pieces does not matter; kexec_load()'d kdump images still function for hotplug as-is. Link: https://lkml.kernel.org/r/20230814214446.6659-7-eric.devolder@oracle.com Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> Suggested-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Baoquan He <bhe@redhat.com> Cc: Akhil Raj <lf32.dev@gmail.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Borislav Petkov (AMD) <bp@alien8.de> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dave Young <dyoung@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Mimi Zohar <zohar@linux.ibm.com> Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Sean Christopherson <seanjc@google.com> Cc: Sourabh Jain <sourabhjain@linux.ibm.com> Cc: Takashi Iwai <tiwai@suse.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
302 lines
7.4 KiB
C
302 lines
7.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* kexec.c - kexec_load system call
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* Copyright (C) 2002-2004 Eric Biederman <ebiederm@xmission.com>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/capability.h>
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#include <linux/mm.h>
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#include <linux/file.h>
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#include <linux/security.h>
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#include <linux/kexec.h>
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#include <linux/mutex.h>
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#include <linux/list.h>
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#include <linux/syscalls.h>
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#include <linux/vmalloc.h>
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#include <linux/slab.h>
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#include "kexec_internal.h"
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static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
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unsigned long nr_segments,
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struct kexec_segment *segments,
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unsigned long flags)
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{
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int ret;
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struct kimage *image;
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bool kexec_on_panic = flags & KEXEC_ON_CRASH;
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if (kexec_on_panic) {
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/* Verify we have a valid entry point */
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if ((entry < phys_to_boot_phys(crashk_res.start)) ||
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(entry > phys_to_boot_phys(crashk_res.end)))
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return -EADDRNOTAVAIL;
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}
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/* Allocate and initialize a controlling structure */
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image = do_kimage_alloc_init();
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if (!image)
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return -ENOMEM;
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image->start = entry;
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image->nr_segments = nr_segments;
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memcpy(image->segment, segments, nr_segments * sizeof(*segments));
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if (kexec_on_panic) {
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/* Enable special crash kernel control page alloc policy. */
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image->control_page = crashk_res.start;
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image->type = KEXEC_TYPE_CRASH;
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}
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ret = sanity_check_segment_list(image);
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if (ret)
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goto out_free_image;
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/*
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* Find a location for the control code buffer, and add it
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* the vector of segments so that it's pages will also be
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* counted as destination pages.
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*/
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ret = -ENOMEM;
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image->control_code_page = kimage_alloc_control_pages(image,
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get_order(KEXEC_CONTROL_PAGE_SIZE));
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if (!image->control_code_page) {
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pr_err("Could not allocate control_code_buffer\n");
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goto out_free_image;
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}
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if (!kexec_on_panic) {
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image->swap_page = kimage_alloc_control_pages(image, 0);
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if (!image->swap_page) {
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pr_err("Could not allocate swap buffer\n");
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goto out_free_control_pages;
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}
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}
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*rimage = image;
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return 0;
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out_free_control_pages:
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kimage_free_page_list(&image->control_pages);
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out_free_image:
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kfree(image);
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return ret;
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}
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static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
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struct kexec_segment *segments, unsigned long flags)
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{
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struct kimage **dest_image, *image;
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unsigned long i;
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int ret;
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/*
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* Because we write directly to the reserved memory region when loading
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* crash kernels we need a serialization here to prevent multiple crash
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* kernels from attempting to load simultaneously.
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*/
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if (!kexec_trylock())
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return -EBUSY;
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if (flags & KEXEC_ON_CRASH) {
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dest_image = &kexec_crash_image;
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if (kexec_crash_image)
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arch_kexec_unprotect_crashkres();
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} else {
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dest_image = &kexec_image;
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}
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if (nr_segments == 0) {
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/* Uninstall image */
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kimage_free(xchg(dest_image, NULL));
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ret = 0;
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goto out_unlock;
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}
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if (flags & KEXEC_ON_CRASH) {
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/*
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* Loading another kernel to switch to if this one
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* crashes. Free any current crash dump kernel before
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* we corrupt it.
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*/
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kimage_free(xchg(&kexec_crash_image, NULL));
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}
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ret = kimage_alloc_init(&image, entry, nr_segments, segments, flags);
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if (ret)
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goto out_unlock;
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if (flags & KEXEC_PRESERVE_CONTEXT)
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image->preserve_context = 1;
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#ifdef CONFIG_CRASH_HOTPLUG
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if (flags & KEXEC_UPDATE_ELFCOREHDR)
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image->update_elfcorehdr = 1;
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#endif
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ret = machine_kexec_prepare(image);
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if (ret)
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goto out;
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/*
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* Some architecture(like S390) may touch the crash memory before
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* machine_kexec_prepare(), we must copy vmcoreinfo data after it.
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*/
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ret = kimage_crash_copy_vmcoreinfo(image);
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if (ret)
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goto out;
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for (i = 0; i < nr_segments; i++) {
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ret = kimage_load_segment(image, &image->segment[i]);
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if (ret)
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goto out;
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}
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kimage_terminate(image);
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ret = machine_kexec_post_load(image);
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if (ret)
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goto out;
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/* Install the new kernel and uninstall the old */
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image = xchg(dest_image, image);
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out:
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if ((flags & KEXEC_ON_CRASH) && kexec_crash_image)
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arch_kexec_protect_crashkres();
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kimage_free(image);
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out_unlock:
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kexec_unlock();
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return ret;
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}
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/*
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* Exec Kernel system call: for obvious reasons only root may call it.
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*
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* This call breaks up into three pieces.
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* - A generic part which loads the new kernel from the current
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* address space, and very carefully places the data in the
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* allocated pages.
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*
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* - A generic part that interacts with the kernel and tells all of
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* the devices to shut down. Preventing on-going dmas, and placing
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* the devices in a consistent state so a later kernel can
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* reinitialize them.
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*
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* - A machine specific part that includes the syscall number
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* and then copies the image to it's final destination. And
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* jumps into the image at entry.
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*
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* kexec does not sync, or unmount filesystems so if you need
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* that to happen you need to do that yourself.
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*/
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static inline int kexec_load_check(unsigned long nr_segments,
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unsigned long flags)
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{
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int image_type = (flags & KEXEC_ON_CRASH) ?
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KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
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int result;
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/* We only trust the superuser with rebooting the system. */
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if (!kexec_load_permitted(image_type))
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return -EPERM;
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/* Permit LSMs and IMA to fail the kexec */
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result = security_kernel_load_data(LOADING_KEXEC_IMAGE, false);
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if (result < 0)
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return result;
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/*
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* kexec can be used to circumvent module loading restrictions, so
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* prevent loading in that case
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*/
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result = security_locked_down(LOCKDOWN_KEXEC);
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if (result)
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return result;
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/*
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* Verify we have a legal set of flags
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* This leaves us room for future extensions.
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*/
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if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))
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return -EINVAL;
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/* Put an artificial cap on the number
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* of segments passed to kexec_load.
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*/
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if (nr_segments > KEXEC_SEGMENT_MAX)
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return -EINVAL;
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return 0;
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}
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SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
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struct kexec_segment __user *, segments, unsigned long, flags)
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{
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struct kexec_segment *ksegments;
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unsigned long result;
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result = kexec_load_check(nr_segments, flags);
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if (result)
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return result;
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/* Verify we are on the appropriate architecture */
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if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&
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((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))
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return -EINVAL;
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ksegments = memdup_user(segments, nr_segments * sizeof(ksegments[0]));
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if (IS_ERR(ksegments))
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return PTR_ERR(ksegments);
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result = do_kexec_load(entry, nr_segments, ksegments, flags);
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kfree(ksegments);
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return result;
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}
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#ifdef CONFIG_COMPAT
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COMPAT_SYSCALL_DEFINE4(kexec_load, compat_ulong_t, entry,
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compat_ulong_t, nr_segments,
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struct compat_kexec_segment __user *, segments,
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compat_ulong_t, flags)
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{
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struct compat_kexec_segment in;
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struct kexec_segment *ksegments;
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unsigned long i, result;
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result = kexec_load_check(nr_segments, flags);
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if (result)
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return result;
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/* Don't allow clients that don't understand the native
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* architecture to do anything.
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*/
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if ((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_DEFAULT)
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return -EINVAL;
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ksegments = kmalloc_array(nr_segments, sizeof(ksegments[0]),
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GFP_KERNEL);
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if (!ksegments)
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return -ENOMEM;
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for (i = 0; i < nr_segments; i++) {
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result = copy_from_user(&in, &segments[i], sizeof(in));
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if (result)
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goto fail;
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ksegments[i].buf = compat_ptr(in.buf);
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ksegments[i].bufsz = in.bufsz;
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ksegments[i].mem = in.mem;
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ksegments[i].memsz = in.memsz;
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}
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result = do_kexec_load(entry, nr_segments, ksegments, flags);
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fail:
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kfree(ksegments);
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return result;
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}
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#endif
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