userns: prevent speculative execution

[mirror_ubuntu-artful-kernel.git] / kernel / kexec_file.c

/*
 * kexec: kexec_file_load system call
 *
 * Copyright (C) 2014 Red Hat Inc.
 * Authors:
 *      Vivek Goyal <vgoyal@redhat.com>
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/capability.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/kexec.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/fs.h>
#include <linux/ima.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <linux/syscalls.h>
#include <linux/vmalloc.h>
#include "kexec_internal.h"

static int kexec_calculate_store_digests(struct kimage *image);

/* Architectures can provide this probe function */
int __weak arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
                                         unsigned long buf_len)
{
        return -ENOEXEC;
}

void * __weak arch_kexec_kernel_image_load(struct kimage *image)
{
        return ERR_PTR(-ENOEXEC);
}

int __weak arch_kimage_file_post_load_cleanup(struct kimage *image)
{
        return -EINVAL;
}

#ifdef CONFIG_KEXEC_VERIFY_SIG
int __weak arch_kexec_kernel_verify_sig(struct kimage *image, void *buf,
                                        unsigned long buf_len)
{
        return -EKEYREJECTED;
}
#endif

/* Apply relocations of type RELA */
int __weak
arch_kexec_apply_relocations_add(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
                                 unsigned int relsec)
{
        pr_err("RELA relocation unsupported.\n");
        return -ENOEXEC;
}

/* Apply relocations of type REL */
int __weak
arch_kexec_apply_relocations(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
                             unsigned int relsec)
{
        pr_err("REL relocation unsupported.\n");
        return -ENOEXEC;
}

/*
 * Free up memory used by kernel, initrd, and command line. This is temporary
 * memory allocation which is not needed any more after these buffers have
 * been loaded into separate segments and have been copied elsewhere.
 */
void kimage_file_post_load_cleanup(struct kimage *image)
{
        struct purgatory_info *pi = &image->purgatory_info;

        vfree(image->kernel_buf);
        image->kernel_buf = NULL;

        vfree(image->initrd_buf);
        image->initrd_buf = NULL;

        kfree(image->cmdline_buf);
        image->cmdline_buf = NULL;

        vfree(pi->purgatory_buf);
        pi->purgatory_buf = NULL;

        vfree(pi->sechdrs);
        pi->sechdrs = NULL;

        /* See if architecture has anything to cleanup post load */
        arch_kimage_file_post_load_cleanup(image);

        /*
         * Above call should have called into bootloader to free up
         * any data stored in kimage->image_loader_data. It should
         * be ok now to free it up.
         */
        kfree(image->image_loader_data);
        image->image_loader_data = NULL;
}

/*
 * In file mode list of segments is prepared by kernel. Copy relevant
 * data from user space, do error checking, prepare segment list
 */
static int
kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
                             const char __user *cmdline_ptr,
                             unsigned long cmdline_len, unsigned flags)
{
        int ret = 0;
        void *ldata;
        loff_t size;

        ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
                                       &size, INT_MAX, READING_KEXEC_IMAGE);
        if (ret)
                return ret;
        image->kernel_buf_len = size;

        /* IMA needs to pass the measurement list to the next kernel. */
        ima_add_kexec_buffer(image);

        /* Call arch image probe handlers */
        ret = arch_kexec_kernel_image_probe(image, image->kernel_buf,
                                            image->kernel_buf_len);
        if (ret)
                goto out;

#ifdef CONFIG_KEXEC_VERIFY_SIG
        ret = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
                                           image->kernel_buf_len);
        if (ret) {
                pr_debug("kernel signature verification failed.\n");
                goto out;
        }
        pr_debug("kernel signature verification successful.\n");
#endif
        /* It is possible that there no initramfs is being loaded */
        if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
                ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,
                                               &size, INT_MAX,
                                               READING_KEXEC_INITRAMFS);
                if (ret)
                        goto out;
                image->initrd_buf_len = size;
        }

        if (cmdline_len) {
                image->cmdline_buf = memdup_user(cmdline_ptr, cmdline_len);
                if (IS_ERR(image->cmdline_buf)) {
                        ret = PTR_ERR(image->cmdline_buf);
                        image->cmdline_buf = NULL;
                        goto out;
                }

                image->cmdline_buf_len = cmdline_len;

                /* command line should be a string with last byte null */
                if (image->cmdline_buf[cmdline_len - 1] != '\0') {
                        ret = -EINVAL;
                        goto out;
                }
        }

        /* Call arch image load handlers */
        ldata = arch_kexec_kernel_image_load(image);

        if (IS_ERR(ldata)) {
                ret = PTR_ERR(ldata);
                goto out;
        }

        image->image_loader_data = ldata;
out:
        /* In case of error, free up all allocated memory in this function */
        if (ret)
                kimage_file_post_load_cleanup(image);
        return ret;
}

static int
kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
                       int initrd_fd, const char __user *cmdline_ptr,
                       unsigned long cmdline_len, unsigned long flags)
{
        int ret;
        struct kimage *image;
        bool kexec_on_panic = flags & KEXEC_FILE_ON_CRASH;

        image = do_kimage_alloc_init();
        if (!image)
                return -ENOMEM;

        image->file_mode = 1;

        if (kexec_on_panic) {
                /* Enable special crash kernel control page alloc policy. */
                image->control_page = crashk_res.start;
                image->type = KEXEC_TYPE_CRASH;
        }

        ret = kimage_file_prepare_segments(image, kernel_fd, initrd_fd,
                                           cmdline_ptr, cmdline_len, flags);
        if (ret)
                goto out_free_image;

        ret = sanity_check_segment_list(image);
        if (ret)
                goto out_free_post_load_bufs;

        ret = -ENOMEM;
        image->control_code_page = kimage_alloc_control_pages(image,
                                           get_order(KEXEC_CONTROL_PAGE_SIZE));
        if (!image->control_code_page) {
                pr_err("Could not allocate control_code_buffer\n");
                goto out_free_post_load_bufs;
        }

        if (!kexec_on_panic) {
                image->swap_page = kimage_alloc_control_pages(image, 0);
                if (!image->swap_page) {
                        pr_err("Could not allocate swap buffer\n");
                        goto out_free_control_pages;
                }
        }

        *rimage = image;
        return 0;
out_free_control_pages:
        kimage_free_page_list(&image->control_pages);
out_free_post_load_bufs:
        kimage_file_post_load_cleanup(image);
out_free_image:
        kfree(image);
        return ret;
}

SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
                unsigned long, cmdline_len, const char __user *, cmdline_ptr,
                unsigned long, flags)
{
        int ret = 0, i;
        struct kimage **dest_image, *image;

        /* We only trust the superuser with rebooting the system. */
        if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
                return -EPERM;

        /* Don't permit images to be loaded into trusted kernels if we're not
         * going to verify the signature on them
         */
        if (!IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG) && kernel_is_locked_down())
                return -EPERM;

        /* Make sure we have a legal set of flags */
        if (flags != (flags & KEXEC_FILE_FLAGS))
                return -EINVAL;

        image = NULL;

        if (!mutex_trylock(&kexec_mutex))
                return -EBUSY;

        dest_image = &kexec_image;
        if (flags & KEXEC_FILE_ON_CRASH) {
                dest_image = &kexec_crash_image;
                if (kexec_crash_image)
                        arch_kexec_unprotect_crashkres();
        }

        if (flags & KEXEC_FILE_UNLOAD)
                goto exchange;

        /*
         * In case of crash, new kernel gets loaded in reserved region. It is
         * same memory where old crash kernel might be loaded. Free any
         * current crash dump kernel before we corrupt it.
         */
        if (flags & KEXEC_FILE_ON_CRASH)
                kimage_free(xchg(&kexec_crash_image, NULL));

        ret = kimage_file_alloc_init(&image, kernel_fd, initrd_fd, cmdline_ptr,
                                     cmdline_len, flags);
        if (ret)
                goto out;

        ret = machine_kexec_prepare(image);
        if (ret)
                goto out;

        /*
         * Some architecture(like S390) may touch the crash memory before
         * machine_kexec_prepare(), we must copy vmcoreinfo data after it.
         */
        ret = kimage_crash_copy_vmcoreinfo(image);
        if (ret)
                goto out;

        ret = kexec_calculate_store_digests(image);
        if (ret)
                goto out;

        for (i = 0; i < image->nr_segments; i++) {
                struct kexec_segment *ksegment;

                ksegment = &image->segment[i];
                pr_debug("Loading segment %d: buf=0x%p bufsz=0x%zx mem=0x%lx memsz=0x%zx\n",
                         i, ksegment->buf, ksegment->bufsz, ksegment->mem,
                         ksegment->memsz);

                ret = kimage_load_segment(image, &image->segment[i]);
                if (ret)
                        goto out;
        }

        kimage_terminate(image);

        /*
         * Free up any temporary buffers allocated which are not needed
         * after image has been loaded
         */
        kimage_file_post_load_cleanup(image);
exchange:
        image = xchg(dest_image, image);
out:
        if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image)
                arch_kexec_protect_crashkres();

        mutex_unlock(&kexec_mutex);
        kimage_free(image);
        return ret;
}

static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
                                    struct kexec_buf *kbuf)
{
        struct kimage *image = kbuf->image;
        unsigned long temp_start, temp_end;

        temp_end = min(end, kbuf->buf_max);
        temp_start = temp_end - kbuf->memsz;

        do {
                /* align down start */
                temp_start = temp_start & (~(kbuf->buf_align - 1));

                if (temp_start < start || temp_start < kbuf->buf_min)
                        return 0;

                temp_end = temp_start + kbuf->memsz - 1;

                /*
                 * Make sure this does not conflict with any of existing
                 * segments
                 */
                if (kimage_is_destination_range(image, temp_start, temp_end)) {
                        temp_start = temp_start - PAGE_SIZE;
                        continue;
                }

                /* We found a suitable memory range */
                break;
        } while (1);

        /* If we are here, we found a suitable memory range */
        kbuf->mem = temp_start;

        /* Success, stop navigating through remaining System RAM ranges */
        return 1;
}

static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
                                     struct kexec_buf *kbuf)
{
        struct kimage *image = kbuf->image;
        unsigned long temp_start, temp_end;

        temp_start = max(start, kbuf->buf_min);

        do {
                temp_start = ALIGN(temp_start, kbuf->buf_align);
                temp_end = temp_start + kbuf->memsz - 1;

                if (temp_end > end || temp_end > kbuf->buf_max)
                        return 0;
                /*
                 * Make sure this does not conflict with any of existing
                 * segments
                 */
                if (kimage_is_destination_range(image, temp_start, temp_end)) {
                        temp_start = temp_start + PAGE_SIZE;
                        continue;
                }

                /* We found a suitable memory range */
                break;
        } while (1);

        /* If we are here, we found a suitable memory range */
        kbuf->mem = temp_start;

        /* Success, stop navigating through remaining System RAM ranges */
        return 1;
}

static int locate_mem_hole_callback(u64 start, u64 end, void *arg)
{
        struct kexec_buf *kbuf = (struct kexec_buf *)arg;
        unsigned long sz = end - start + 1;

        /* Returning 0 will take to next memory range */
        if (sz < kbuf->memsz)
                return 0;

        if (end < kbuf->buf_min || start > kbuf->buf_max)
                return 0;

        /*
         * Allocate memory top down with-in ram range. Otherwise bottom up
         * allocation.
         */
        if (kbuf->top_down)
                return locate_mem_hole_top_down(start, end, kbuf);
        return locate_mem_hole_bottom_up(start, end, kbuf);
}

/**
 * arch_kexec_walk_mem - call func(data) on free memory regions
 * @kbuf:       Context info for the search. Also passed to @func.
 * @func:       Function to call for each memory region.
 *
 * Return: The memory walk will stop when func returns a non-zero value
 * and that value will be returned. If all free regions are visited without
 * func returning non-zero, then zero will be returned.
 */
int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf,
                               int (*func)(u64, u64, void *))
{
        if (kbuf->image->type == KEXEC_TYPE_CRASH)
                return walk_iomem_res_desc(crashk_res.desc,
                                           IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY,
                                           crashk_res.start, crashk_res.end,
                                           kbuf, func);
        else
                return walk_system_ram_res(0, ULONG_MAX, kbuf, func);
}

/**
 * kexec_locate_mem_hole - find free memory for the purgatory or the next kernel
 * @kbuf:       Parameters for the memory search.
 *
 * On success, kbuf->mem will have the start address of the memory region found.
 *
 * Return: 0 on success, negative errno on error.
 */
int kexec_locate_mem_hole(struct kexec_buf *kbuf)
{
        int ret;

        ret = arch_kexec_walk_mem(kbuf, locate_mem_hole_callback);

        return ret == 1 ? 0 : -EADDRNOTAVAIL;
}

/**
 * kexec_add_buffer - place a buffer in a kexec segment
 * @kbuf:       Buffer contents and memory parameters.
 *
 * This function assumes that kexec_mutex is held.
 * On successful return, @kbuf->mem will have the physical address of
 * the buffer in memory.
 *
 * Return: 0 on success, negative errno on error.
 */
int kexec_add_buffer(struct kexec_buf *kbuf)
{

        struct kexec_segment *ksegment;
        int ret;

        /* Currently adding segment this way is allowed only in file mode */
        if (!kbuf->image->file_mode)
                return -EINVAL;

        if (kbuf->image->nr_segments >= KEXEC_SEGMENT_MAX)
                return -EINVAL;

        /*
         * Make sure we are not trying to add buffer after allocating
         * control pages. All segments need to be placed first before
         * any control pages are allocated. As control page allocation
         * logic goes through list of segments to make sure there are
         * no destination overlaps.
         */
        if (!list_empty(&kbuf->image->control_pages)) {
                WARN_ON(1);
                return -EINVAL;
        }

        /* Ensure minimum alignment needed for segments. */
        kbuf->memsz = ALIGN(kbuf->memsz, PAGE_SIZE);
        kbuf->buf_align = max(kbuf->buf_align, PAGE_SIZE);

        /* Walk the RAM ranges and allocate a suitable range for the buffer */
        ret = kexec_locate_mem_hole(kbuf);
        if (ret)
                return ret;

        /* Found a suitable memory range */
        ksegment = &kbuf->image->segment[kbuf->image->nr_segments];
        ksegment->kbuf = kbuf->buffer;
        ksegment->bufsz = kbuf->bufsz;
        ksegment->mem = kbuf->mem;
        ksegment->memsz = kbuf->memsz;
        kbuf->image->nr_segments++;
        return 0;
}

/* Calculate and store the digest of segments */
static int kexec_calculate_store_digests(struct kimage *image)
{
        struct crypto_shash *tfm;
        struct shash_desc *desc;
        int ret = 0, i, j, zero_buf_sz, sha_region_sz;
        size_t desc_size, nullsz;
        char *digest;
        void *zero_buf;
        struct kexec_sha_region *sha_regions;
        struct purgatory_info *pi = &image->purgatory_info;

        zero_buf = __va(page_to_pfn(ZERO_PAGE(0)) << PAGE_SHIFT);
        zero_buf_sz = PAGE_SIZE;

        tfm = crypto_alloc_shash("sha256", 0, 0);
        if (IS_ERR(tfm)) {
                ret = PTR_ERR(tfm);
                goto out;
        }

        desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
        desc = kzalloc(desc_size, GFP_KERNEL);
        if (!desc) {
                ret = -ENOMEM;
                goto out_free_tfm;
        }

        sha_region_sz = KEXEC_SEGMENT_MAX * sizeof(struct kexec_sha_region);
        sha_regions = vzalloc(sha_region_sz);
        if (!sha_regions)
                goto out_free_desc;

        desc->tfm   = tfm;
        desc->flags = 0;

        ret = crypto_shash_init(desc);
        if (ret < 0)
                goto out_free_sha_regions;

        digest = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
        if (!digest) {
                ret = -ENOMEM;
                goto out_free_sha_regions;
        }

        for (j = i = 0; i < image->nr_segments; i++) {
                struct kexec_segment *ksegment;

                ksegment = &image->segment[i];
                /*
                 * Skip purgatory as it will be modified once we put digest
                 * info in purgatory.
                 */
                if (ksegment->kbuf == pi->purgatory_buf)
                        continue;

                ret = crypto_shash_update(desc, ksegment->kbuf,
                                          ksegment->bufsz);
                if (ret)
                        break;

                /*
                 * Assume rest of the buffer is filled with zero and
                 * update digest accordingly.
                 */
                nullsz = ksegment->memsz - ksegment->bufsz;
                while (nullsz) {
                        unsigned long bytes = nullsz;

                        if (bytes > zero_buf_sz)
                                bytes = zero_buf_sz;
                        ret = crypto_shash_update(desc, zero_buf, bytes);
                        if (ret)
                                break;
                        nullsz -= bytes;
                }

                if (ret)
                        break;

                sha_regions[j].start = ksegment->mem;
                sha_regions[j].len = ksegment->memsz;
                j++;
        }

        if (!ret) {
                ret = crypto_shash_final(desc, digest);
                if (ret)
                        goto out_free_digest;
                ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha_regions",
                                                     sha_regions, sha_region_sz, 0);
                if (ret)
                        goto out_free_digest;

                ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha256_digest",
                                                     digest, SHA256_DIGEST_SIZE, 0);
                if (ret)
                        goto out_free_digest;
        }

out_free_digest:
        kfree(digest);
out_free_sha_regions:
        vfree(sha_regions);
out_free_desc:
        kfree(desc);
out_free_tfm:
        kfree(tfm);
out:
        return ret;
}

/* Actually load purgatory. Lot of code taken from kexec-tools */
static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
                                  unsigned long max, int top_down)
{
        struct purgatory_info *pi = &image->purgatory_info;
        unsigned long align, bss_align, bss_sz, bss_pad;
        unsigned long entry, load_addr, curr_load_addr, bss_addr, offset;
        unsigned char *buf_addr, *src;
        int i, ret = 0, entry_sidx = -1;
        const Elf_Shdr *sechdrs_c;
        Elf_Shdr *sechdrs = NULL;
        struct kexec_buf kbuf = { .image = image, .bufsz = 0, .buf_align = 1,
                                  .buf_min = min, .buf_max = max,
                                  .top_down = top_down };

        /*
         * sechdrs_c points to section headers in purgatory and are read
         * only. No modifications allowed.
         */
        sechdrs_c = (void *)pi->ehdr + pi->ehdr->e_shoff;

        /*
         * We can not modify sechdrs_c[] and its fields. It is read only.
         * Copy it over to a local copy where one can store some temporary
         * data and free it at the end. We need to modify ->sh_addr and
         * ->sh_offset fields to keep track of permanent and temporary
         * locations of sections.
         */
        sechdrs = vzalloc(pi->ehdr->e_shnum * sizeof(Elf_Shdr));
        if (!sechdrs)
                return -ENOMEM;

        memcpy(sechdrs, sechdrs_c, pi->ehdr->e_shnum * sizeof(Elf_Shdr));

        /*
         * We seem to have multiple copies of sections. First copy is which
         * is embedded in kernel in read only section. Some of these sections
         * will be copied to a temporary buffer and relocated. And these
         * sections will finally be copied to their final destination at
         * segment load time.
         *
         * Use ->sh_offset to reflect section address in memory. It will
         * point to original read only copy if section is not allocatable.
         * Otherwise it will point to temporary copy which will be relocated.
         *
         * Use ->sh_addr to contain final address of the section where it
         * will go during execution time.
         */
        for (i = 0; i < pi->ehdr->e_shnum; i++) {
                if (sechdrs[i].sh_type == SHT_NOBITS)
                        continue;

                sechdrs[i].sh_offset = (unsigned long)pi->ehdr +
                                                sechdrs[i].sh_offset;
        }

        /*
         * Identify entry point section and make entry relative to section
         * start.
         */
        entry = pi->ehdr->e_entry;
        for (i = 0; i < pi->ehdr->e_shnum; i++) {
                if (!(sechdrs[i].sh_flags & SHF_ALLOC))
                        continue;

                if (!(sechdrs[i].sh_flags & SHF_EXECINSTR))
                        continue;

                /* Make entry section relative */
                if (sechdrs[i].sh_addr <= pi->ehdr->e_entry &&
                    ((sechdrs[i].sh_addr + sechdrs[i].sh_size) >
                     pi->ehdr->e_entry)) {
                        entry_sidx = i;
                        entry -= sechdrs[i].sh_addr;
                        break;
                }
        }

        /* Determine how much memory is needed to load relocatable object. */
        bss_align = 1;
        bss_sz = 0;

        for (i = 0; i < pi->ehdr->e_shnum; i++) {
                if (!(sechdrs[i].sh_flags & SHF_ALLOC))
                        continue;

                align = sechdrs[i].sh_addralign;
                if (sechdrs[i].sh_type != SHT_NOBITS) {
                        if (kbuf.buf_align < align)
                                kbuf.buf_align = align;
                        kbuf.bufsz = ALIGN(kbuf.bufsz, align);
                        kbuf.bufsz += sechdrs[i].sh_size;
                } else {
                        /* bss section */
                        if (bss_align < align)
                                bss_align = align;
                        bss_sz = ALIGN(bss_sz, align);
                        bss_sz += sechdrs[i].sh_size;
                }
        }

        /* Determine the bss padding required to align bss properly */
        bss_pad = 0;
        if (kbuf.bufsz & (bss_align - 1))
                bss_pad = bss_align - (kbuf.bufsz & (bss_align - 1));

        kbuf.memsz = kbuf.bufsz + bss_pad + bss_sz;

        /* Allocate buffer for purgatory */
        kbuf.buffer = vzalloc(kbuf.bufsz);
        if (!kbuf.buffer) {
                ret = -ENOMEM;
                goto out;
        }

        if (kbuf.buf_align < bss_align)
                kbuf.buf_align = bss_align;

        /* Add buffer to segment list */
        ret = kexec_add_buffer(&kbuf);
        if (ret)
                goto out;
        pi->purgatory_load_addr = kbuf.mem;

        /* Load SHF_ALLOC sections */
        buf_addr = kbuf.buffer;
        load_addr = curr_load_addr = pi->purgatory_load_addr;
        bss_addr = load_addr + kbuf.bufsz + bss_pad;

        for (i = 0; i < pi->ehdr->e_shnum; i++) {
                if (!(sechdrs[i].sh_flags & SHF_ALLOC))
                        continue;

                align = sechdrs[i].sh_addralign;
                if (sechdrs[i].sh_type != SHT_NOBITS) {
                        curr_load_addr = ALIGN(curr_load_addr, align);
                        offset = curr_load_addr - load_addr;
                        /* We already modifed ->sh_offset to keep src addr */
                        src = (char *) sechdrs[i].sh_offset;
                        memcpy(buf_addr + offset, src, sechdrs[i].sh_size);

                        /* Store load address and source address of section */
                        sechdrs[i].sh_addr = curr_load_addr;

                        /*
                         * This section got copied to temporary buffer. Update
                         * ->sh_offset accordingly.
                         */
                        sechdrs[i].sh_offset = (unsigned long)(buf_addr + offset);

                        /* Advance to the next address */
                        curr_load_addr += sechdrs[i].sh_size;
                } else {
                        bss_addr = ALIGN(bss_addr, align);
                        sechdrs[i].sh_addr = bss_addr;
                        bss_addr += sechdrs[i].sh_size;
                }
        }

        /* Update entry point based on load address of text section */
        if (entry_sidx >= 0)
                entry += sechdrs[entry_sidx].sh_addr;

        /* Make kernel jump to purgatory after shutdown */
        image->start = entry;

        /* Used later to get/set symbol values */
        pi->sechdrs = sechdrs;

        /*
         * Used later to identify which section is purgatory and skip it
         * from checksumming.
         */
        pi->purgatory_buf = kbuf.buffer;
        return ret;
out:
        vfree(sechdrs);
        vfree(kbuf.buffer);
        return ret;
}

static int kexec_apply_relocations(struct kimage *image)
{
        int i, ret;
        struct purgatory_info *pi = &image->purgatory_info;
        Elf_Shdr *sechdrs = pi->sechdrs;

        /* Apply relocations */
        for (i = 0; i < pi->ehdr->e_shnum; i++) {
                Elf_Shdr *section, *symtab;

                if (sechdrs[i].sh_type != SHT_RELA &&
                    sechdrs[i].sh_type != SHT_REL)
                        continue;

                /*
                 * For section of type SHT_RELA/SHT_REL,
                 * ->sh_link contains section header index of associated
                 * symbol table. And ->sh_info contains section header
                 * index of section to which relocations apply.
                 */
                if (sechdrs[i].sh_info >= pi->ehdr->e_shnum ||
                    sechdrs[i].sh_link >= pi->ehdr->e_shnum)
                        return -ENOEXEC;

                section = &sechdrs[sechdrs[i].sh_info];
                symtab = &sechdrs[sechdrs[i].sh_link];

                if (!(section->sh_flags & SHF_ALLOC))
                        continue;

                /*
                 * symtab->sh_link contain section header index of associated
                 * string table.
                 */
                if (symtab->sh_link >= pi->ehdr->e_shnum)
                        /* Invalid section number? */
                        continue;

                /*
                 * Respective architecture needs to provide support for applying
                 * relocations of type SHT_RELA/SHT_REL.
                 */
                if (sechdrs[i].sh_type == SHT_RELA)
                        ret = arch_kexec_apply_relocations_add(pi->ehdr,
                                                               sechdrs, i);
                else if (sechdrs[i].sh_type == SHT_REL)
                        ret = arch_kexec_apply_relocations(pi->ehdr,
                                                           sechdrs, i);
                if (ret)
                        return ret;
        }

        return 0;
}

/* Load relocatable purgatory object and relocate it appropriately */
int kexec_load_purgatory(struct kimage *image, unsigned long min,
                         unsigned long max, int top_down,
                         unsigned long *load_addr)
{
        struct purgatory_info *pi = &image->purgatory_info;
        int ret;

        if (kexec_purgatory_size <= 0)
                return -EINVAL;

        if (kexec_purgatory_size < sizeof(Elf_Ehdr))
                return -ENOEXEC;

        pi->ehdr = (Elf_Ehdr *)kexec_purgatory;

        if (memcmp(pi->ehdr->e_ident, ELFMAG, SELFMAG) != 0
            || pi->ehdr->e_type != ET_REL
            || !elf_check_arch(pi->ehdr)
            || pi->ehdr->e_shentsize != sizeof(Elf_Shdr))
                return -ENOEXEC;

        if (pi->ehdr->e_shoff >= kexec_purgatory_size
            || (pi->ehdr->e_shnum * sizeof(Elf_Shdr) >
            kexec_purgatory_size - pi->ehdr->e_shoff))
                return -ENOEXEC;

        ret = __kexec_load_purgatory(image, min, max, top_down);
        if (ret)
                return ret;

        ret = kexec_apply_relocations(image);
        if (ret)
                goto out;

        *load_addr = pi->purgatory_load_addr;
        return 0;
out:
        vfree(pi->sechdrs);
        pi->sechdrs = NULL;

        vfree(pi->purgatory_buf);
        pi->purgatory_buf = NULL;
        return ret;
}

static Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
                                            const char *name)
{
        Elf_Sym *syms;
        Elf_Shdr *sechdrs;
        Elf_Ehdr *ehdr;
        int i, k;
        const char *strtab;

        if (!pi->sechdrs || !pi->ehdr)
                return NULL;

        sechdrs = pi->sechdrs;
        ehdr = pi->ehdr;

        for (i = 0; i < ehdr->e_shnum; i++) {
                if (sechdrs[i].sh_type != SHT_SYMTAB)
                        continue;

                if (sechdrs[i].sh_link >= ehdr->e_shnum)
                        /* Invalid strtab section number */
                        continue;
                strtab = (char *)sechdrs[sechdrs[i].sh_link].sh_offset;
                syms = (Elf_Sym *)sechdrs[i].sh_offset;

                /* Go through symbols for a match */
                for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
                        if (ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
                                continue;

                        if (strcmp(strtab + syms[k].st_name, name) != 0)
                                continue;

                        if (syms[k].st_shndx == SHN_UNDEF ||
                            syms[k].st_shndx >= ehdr->e_shnum) {
                                pr_debug("Symbol: %s has bad section index %d.\n",
                                                name, syms[k].st_shndx);
                                return NULL;
                        }

                        /* Found the symbol we are looking for */
                        return &syms[k];
                }
        }

        return NULL;
}

void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)
{
        struct purgatory_info *pi = &image->purgatory_info;
        Elf_Sym *sym;
        Elf_Shdr *sechdr;

        sym = kexec_purgatory_find_symbol(pi, name);
        if (!sym)
                return ERR_PTR(-EINVAL);

        sechdr = &pi->sechdrs[sym->st_shndx];

        /*
         * Returns the address where symbol will finally be loaded after
         * kexec_load_segment()
         */
        return (void *)(sechdr->sh_addr + sym->st_value);
}

/*
 * Get or set value of a symbol. If "get_value" is true, symbol value is
 * returned in buf otherwise symbol value is set based on value in buf.
 */
int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
                                   void *buf, unsigned int size, bool get_value)
{
        Elf_Sym *sym;
        Elf_Shdr *sechdrs;
        struct purgatory_info *pi = &image->purgatory_info;
        char *sym_buf;

        sym = kexec_purgatory_find_symbol(pi, name);
        if (!sym)
                return -EINVAL;

        if (sym->st_size != size) {
                pr_err("symbol %s size mismatch: expected %lu actual %u\n",
                       name, (unsigned long)sym->st_size, size);
                return -EINVAL;
        }

        sechdrs = pi->sechdrs;

        if (sechdrs[sym->st_shndx].sh_type == SHT_NOBITS) {
                pr_err("symbol %s is in a bss section. Cannot %s\n", name,
                       get_value ? "get" : "set");
                return -EINVAL;
        }

        sym_buf = (unsigned char *)sechdrs[sym->st_shndx].sh_offset +
                                        sym->st_value;

        if (get_value)
                memcpy((void *)buf, sym_buf, size);
        else
                memcpy((void *)sym_buf, buf, size);

        return 0;
}