linux/kernel/crash_core.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * crash.c - kernel crash support code.
 * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
 */

#include <linux/buildid.h>
#include <linux/init.h>
#include <linux/utsname.h>
#include <linux/vmalloc.h>
#include <linux/sizes.h>
#include <linux/kexec.h>
#include <linux/memory.h>
#include <linux/cpuhotplug.h>
#include <linux/memblock.h>
#include <linux/kmemleak.h>

#include <asm/page.h>
#include <asm/sections.h>

#include <crypto/sha1.h>

#include "kallsyms_internal.h"
#include "kexec_internal.h"

/* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes;

int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
			  void **addr, unsigned long *sz)
{
	Elf64_Ehdr *ehdr;
	Elf64_Phdr *phdr;
	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
	unsigned char *buf;
	unsigned int cpu, i;
	unsigned long long notes_addr;
	unsigned long mstart, mend;

	/* extra phdr for vmcoreinfo ELF note */
	nr_phdr = nr_cpus + 1;
	nr_phdr += mem->nr_ranges;

	/*
	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
	 * I think this is required by tools like gdb. So same physical
	 * memory will be mapped in two ELF headers. One will contain kernel
	 * text virtual addresses and other will have __va(physical) addresses.
	 */

	nr_phdr++;
	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);

	buf = vzalloc(elf_sz);
	if (!buf)
		return -ENOMEM;

	ehdr = (Elf64_Ehdr *)buf;
	phdr = (Elf64_Phdr *)(ehdr + 1);
	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
	memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
	ehdr->e_type = ET_CORE;
	ehdr->e_machine = ELF_ARCH;
	ehdr->e_version = EV_CURRENT;
	ehdr->e_phoff = sizeof(Elf64_Ehdr);
	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
	ehdr->e_phentsize = sizeof(Elf64_Phdr);

	/* Prepare one phdr of type PT_NOTE for each possible CPU */
	for_each_possible_cpu(cpu) {
		phdr->p_type = PT_NOTE;
		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
		phdr->p_offset = phdr->p_paddr = notes_addr;
		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
		(ehdr->e_phnum)++;
		phdr++;
	}

	/* Prepare one PT_NOTE header for vmcoreinfo */
	phdr->p_type = PT_NOTE;
	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
	(ehdr->e_phnum)++;
	phdr++;

	/* Prepare PT_LOAD type program header for kernel text region */
	if (need_kernel_map) {
		phdr->p_type = PT_LOAD;
		phdr->p_flags = PF_R|PF_W|PF_X;
		phdr->p_vaddr = (unsigned long) _text;
		phdr->p_filesz = phdr->p_memsz = _end - _text;
		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
		ehdr->e_phnum++;
		phdr++;
	}

	/* Go through all the ranges in mem->ranges[] and prepare phdr */
	for (i = 0; i < mem->nr_ranges; i++) {
		mstart = mem->ranges[i].start;
		mend = mem->ranges[i].end;

		phdr->p_type = PT_LOAD;
		phdr->p_flags = PF_R|PF_W|PF_X;
		phdr->p_offset  = mstart;

		phdr->p_paddr = mstart;
		phdr->p_vaddr = (unsigned long) __va(mstart);
		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
		phdr->p_align = 0;
		ehdr->e_phnum++;
#ifdef CONFIG_KEXEC_FILE
		kexec_dprintk("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
			      phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
			      ehdr->e_phnum, phdr->p_offset);
#endif
		phdr++;
	}

	*addr = buf;
	*sz = elf_sz;
	return 0;
}

int crash_exclude_mem_range(struct crash_mem *mem,
			    unsigned long long mstart, unsigned long long mend)
{
	int i;
	unsigned long long start, end, p_start, p_end;

	for (i = 0; i < mem->nr_ranges; i++) {
		start = mem->ranges[i].start;
		end = mem->ranges[i].end;
		p_start = mstart;
		p_end = mend;

		if (p_start > end)
			continue;

		/*
		 * Because the memory ranges in mem->ranges are stored in
		 * ascending order, when we detect `p_end < start`, we can
		 * immediately exit the for loop, as the subsequent memory
		 * ranges will definitely be outside the range we are looking
		 * for.
		 */
		if (p_end < start)
			break;

		/* Truncate any area outside of range */
		if (p_start < start)
			p_start = start;
		if (p_end > end)
			p_end = end;

		/* Found completely overlapping range */
		if (p_start == start && p_end == end) {
			memmove(&mem->ranges[i], &mem->ranges[i + 1],
				(mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));
			i--;
			mem->nr_ranges--;
		} else if (p_start > start && p_end < end) {
			/* Split original range */
			if (mem->nr_ranges >= mem->max_nr_ranges)
				return -ENOMEM;

			memmove(&mem->ranges[i + 2], &mem->ranges[i + 1],
				(mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));

			mem->ranges[i].end = p_start - 1;
			mem->ranges[i + 1].start = p_end + 1;
			mem->ranges[i + 1].end = end;

			i++;
			mem->nr_ranges++;
		} else if (p_start != start)
			mem->ranges[i].end = p_start - 1;
		else
			mem->ranges[i].start = p_end + 1;
	}

	return 0;
}

static int __init crash_notes_memory_init(void)
{
	/* Allocate memory for saving cpu registers. */
	size_t size, align;

	/*
	 * crash_notes could be allocated across 2 vmalloc pages when percpu
	 * is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
	 * pages are also on 2 continuous physical pages. In this case the
	 * 2nd part of crash_notes in 2nd page could be lost since only the
	 * starting address and size of crash_notes are exported through sysfs.
	 * Here round up the size of crash_notes to the nearest power of two
	 * and pass it to __alloc_percpu as align value. This can make sure
	 * crash_notes is allocated inside one physical page.
	 */
	size = sizeof(note_buf_t);
	align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);

	/*
	 * Break compile if size is bigger than PAGE_SIZE since crash_notes
	 * definitely will be in 2 pages with that.
	 */
	BUILD_BUG_ON(size > PAGE_SIZE);

	crash_notes = __alloc_percpu(size, align);
	if (!crash_notes) {
		pr_warn("Memory allocation for saving cpu register states failed\n");
		return -ENOMEM;
	}
	return 0;
}
subsys_initcall(crash_notes_memory_init);

#ifdef CONFIG_CRASH_HOTPLUG
#undef pr_fmt
#define pr_fmt(fmt) "crash hp: " fmt

/*
 * Different than kexec/kdump loading/unloading/jumping/shrinking which
 * usually rarely happen, there will be many crash hotplug events notified
 * during one short period, e.g one memory board is hot added and memory
 * regions are online. So mutex lock  __crash_hotplug_lock is used to
 * serialize the crash hotplug handling specifically.
 */
static DEFINE_MUTEX(__crash_hotplug_lock);
#define crash_hotplug_lock() mutex_lock(&__crash_hotplug_lock)
#define crash_hotplug_unlock() mutex_unlock(&__crash_hotplug_lock)

/*
 * This routine utilized when the crash_hotplug sysfs node is read.
 * It reflects the kernel's ability/permission to update the crash
 * elfcorehdr directly.
 */
int crash_check_update_elfcorehdr(void)
{
	int rc = 0;

	crash_hotplug_lock();
	/* Obtain lock while reading crash information */
	if (!kexec_trylock()) {
		pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
		crash_hotplug_unlock();
		return 0;
	}
	if (kexec_crash_image) {
		if (kexec_crash_image->file_mode)
			rc = 1;
		else
			rc = kexec_crash_image->update_elfcorehdr;
	}
	/* Release lock now that update complete */
	kexec_unlock();
	crash_hotplug_unlock();

	return rc;
}

/*
 * To accurately reflect hot un/plug changes of cpu and memory resources
 * (including onling and offlining of those resources), the elfcorehdr
 * (which is passed to the crash kernel via the elfcorehdr= parameter)
 * must be updated with the new list of CPUs and memories.
 *
 * In order to make changes to elfcorehdr, two conditions are needed:
 * First, the segment containing the elfcorehdr must be large enough
 * to permit a growing number of resources; the elfcorehdr memory size
 * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES.
 * Second, purgatory must explicitly exclude the elfcorehdr from the
 * list of segments it checks (since the elfcorehdr changes and thus
 * would require an update to purgatory itself to update the digest).
 */
static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
{
	struct kimage *image;

	crash_hotplug_lock();
	/* Obtain lock while changing crash information */
	if (!kexec_trylock()) {
		pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
		crash_hotplug_unlock();
		return;
	}

	/* Check kdump is not loaded */
	if (!kexec_crash_image)
		goto out;

	image = kexec_crash_image;

	/* Check that updating elfcorehdr is permitted */
	if (!(image->file_mode || image->update_elfcorehdr))
		goto out;

	if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
		hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
		pr_debug("hp_action %u, cpu %u\n", hp_action, cpu);
	else
		pr_debug("hp_action %u\n", hp_action);

	/*
	 * The elfcorehdr_index is set to -1 when the struct kimage
	 * is allocated. Find the segment containing the elfcorehdr,
	 * if not already found.
	 */
	if (image->elfcorehdr_index < 0) {
		unsigned long mem;
		unsigned char *ptr;
		unsigned int n;

		for (n = 0; n < image->nr_segments; n++) {
			mem = image->segment[n].mem;
			ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
			if (ptr) {
				/* The segment containing elfcorehdr */
				if (memcmp(ptr, ELFMAG, SELFMAG) == 0)
					image->elfcorehdr_index = (int)n;
				kunmap_local(ptr);
			}
		}
	}

	if (image->elfcorehdr_index < 0) {
		pr_err("unable to locate elfcorehdr segment");
		goto out;
	}

	/* Needed in order for the segments to be updated */
	arch_kexec_unprotect_crashkres();

	/* Differentiate between normal load and hotplug update */
	image->hp_action = hp_action;

	/* Now invoke arch-specific update handler */
	arch_crash_handle_hotplug_event(image);

	/* No longer handling a hotplug event */
	image->hp_action = KEXEC_CRASH_HP_NONE;
	image->elfcorehdr_updated = true;

	/* Change back to read-only */
	arch_kexec_protect_crashkres();

	/* Errors in the callback is not a reason to rollback state */
out:
	/* Release lock now that update complete */
	kexec_unlock();
	crash_hotplug_unlock();
}

static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
{
	switch (val) {
	case MEM_ONLINE:
		crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY,
			KEXEC_CRASH_HP_INVALID_CPU);
		break;

	case MEM_OFFLINE:
		crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY,
			KEXEC_CRASH_HP_INVALID_CPU);
		break;
	}
	return NOTIFY_OK;
}

static struct notifier_block crash_memhp_nb = {
	.notifier_call = crash_memhp_notifier,
	.priority = 0
};

static int crash_cpuhp_online(unsigned int cpu)
{
	crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
	return 0;
}

static int crash_cpuhp_offline(unsigned int cpu)
{
	crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
	return 0;
}

static int __init crash_hotplug_init(void)
{
	int result = 0;

	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
		register_memory_notifier(&crash_memhp_nb);

	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
		result = cpuhp_setup_state_nocalls(CPUHP_BP_PREPARE_DYN,
			"crash/cpuhp", crash_cpuhp_online, crash_cpuhp_offline);
	}

	return result;
}

subsys_initcall(crash_hotplug_init);
#endif