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![Ricardo Ribalda](/assets/img/avatar_default.png)
kexec allows replacing the current kernel with a different one. This is usually a source of concerns for sysadmins that want to harden a system. Linux already provides a way to disable loading new kexec kernel via kexec_load_disabled, but that control is very coard, it is all or nothing and does not make distinction between a panic kexec and a normal kexec. This patch introduces new sysctl parameters, with finer tuning to specify how many times a kexec kernel can be loaded. The sysadmin can set different limits for kexec panic and kexec reboot kernels. The value can be modified at runtime via sysctl, but only with a stricter value. With these new parameters on place, a system with loadpin and verity enabled, using the following kernel parameters: sysctl.kexec_load_limit_reboot=0 sysct.kexec_load_limit_panic=1 can have a good warranty that if initrd tries to load a panic kernel, a malitious user will have small chances to replace that kernel with a different one, even if they can trigger timeouts on the disk where the panic kernel lives. Link: https://lkml.kernel.org/r/20221114-disable-kexec-reset-v6-3-6a8531a09b9a@chromium.org Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Acked-by: Baoquan He <bhe@redhat.com> Cc: Bagas Sanjaya <bagasdotme@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck Cc: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Philipp Rudo <prudo@redhat.com> Cc: Ross Zwisler <zwisler@kernel.org> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
297 lines
7.3 KiB
C
297 lines
7.3 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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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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