// SPDX-License-Identifier: GPL-2.0-only
/*
 * Load ELF vmlinux file for the kexec_file_load syscall.
 *
 * Copyright (C) 2004  Adam Litke (agl@us.ibm.com)
 * Copyright (C) 2004  IBM Corp.
 * Copyright (C) 2005  R Sharada (sharada@in.ibm.com)
 * Copyright (C) 2006  Mohan Kumar M (mohan@in.ibm.com)
 * Copyright (C) 2016  IBM Corporation
 *
 * Based on kexec-tools' kexec-elf-exec.c and kexec-elf-ppc64.c.
 * Heavily modified for the kernel by
 * Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>.
 */

#define pr_fmt(fmt)     "kexec_elf: " fmt

#include <linux/elf.h>
#include <linux/kexec.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>

static inline bool elf_is_elf_file(const struct elfhdr *ehdr)
{
        return memcmp(ehdr->e_ident, ELFMAG, SELFMAG) == 0;
}

static uint64_t elf64_to_cpu(const struct elfhdr *ehdr, uint64_t value)
{
        if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
                value = le64_to_cpu(value);
        else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
                value = be64_to_cpu(value);

        return value;
}

static uint32_t elf32_to_cpu(const struct elfhdr *ehdr, uint32_t value)
{
        if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
                value = le32_to_cpu(value);
        else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
                value = be32_to_cpu(value);

        return value;
}

static uint16_t elf16_to_cpu(const struct elfhdr *ehdr, uint16_t value)
{
        if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
                value = le16_to_cpu(value);
        else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
                value = be16_to_cpu(value);

        return value;
}

/**
 * elf_is_ehdr_sane - check that it is safe to use the ELF header
 * @buf_len:    size of the buffer in which the ELF file is loaded.
 */
static bool elf_is_ehdr_sane(const struct elfhdr *ehdr, size_t buf_len)
{
        if (ehdr->e_phnum > 0 && ehdr->e_phentsize != sizeof(struct elf_phdr)) {
                pr_debug("Bad program header size.\n");
                return false;
        } else if (ehdr->e_shnum > 0 &&
                   ehdr->e_shentsize != sizeof(struct elf_shdr)) {
                pr_debug("Bad section header size.\n");
                return false;
        } else if (ehdr->e_ident[EI_VERSION] != EV_CURRENT ||
                   ehdr->e_version != EV_CURRENT) {
                pr_debug("Unknown ELF version.\n");
                return false;
        }

        if (ehdr->e_phoff > 0 && ehdr->e_phnum > 0) {
                size_t phdr_size;

                /*
                 * e_phnum is at most 65535 so calculating the size of the
                 * program header cannot overflow.
                 */
                phdr_size = sizeof(struct elf_phdr) * ehdr->e_phnum;

                /* Sanity check the program header table location. */
                if (ehdr->e_phoff + phdr_size < ehdr->e_phoff) {
                        pr_debug("Program headers at invalid location.\n");
                        return false;
                } else if (ehdr->e_phoff + phdr_size > buf_len) {
                        pr_debug("Program headers truncated.\n");
                        return false;
                }
        }

        if (ehdr->e_shoff > 0 && ehdr->e_shnum > 0) {
                size_t shdr_size;

                /*
                 * e_shnum is at most 65536 so calculating
                 * the size of the section header cannot overflow.
                 */
                shdr_size = sizeof(struct elf_shdr) * ehdr->e_shnum;

                /* Sanity check the section header table location. */
                if (ehdr->e_shoff + shdr_size < ehdr->e_shoff) {
                        pr_debug("Section headers at invalid location.\n");
                        return false;
                } else if (ehdr->e_shoff + shdr_size > buf_len) {
                        pr_debug("Section headers truncated.\n");
                        return false;
                }
        }

        return true;
}

static int elf_read_ehdr(const char *buf, size_t len, struct elfhdr *ehdr)
{
        struct elfhdr *buf_ehdr;

        if (len < sizeof(*buf_ehdr)) {
                pr_debug("Buffer is too small to hold ELF header.\n");
                return -ENOEXEC;
        }

        memset(ehdr, 0, sizeof(*ehdr));
        memcpy(ehdr->e_ident, buf, sizeof(ehdr->e_ident));
        if (!elf_is_elf_file(ehdr)) {
                pr_debug("No ELF header magic.\n");
                return -ENOEXEC;
        }

        if (ehdr->e_ident[EI_CLASS] != ELF_CLASS) {
                pr_debug("Not a supported ELF class.\n");
                return -ENOEXEC;
        } else  if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB &&
                ehdr->e_ident[EI_DATA] != ELFDATA2MSB) {
                pr_debug("Not a supported ELF data format.\n");
                return -ENOEXEC;
        }

        buf_ehdr = (struct elfhdr *) buf;
        if (elf16_to_cpu(ehdr, buf_ehdr->e_ehsize) != sizeof(*buf_ehdr)) {
                pr_debug("Bad ELF header size.\n");
                return -ENOEXEC;
        }

        ehdr->e_type      = elf16_to_cpu(ehdr, buf_ehdr->e_type);
        ehdr->e_machine   = elf16_to_cpu(ehdr, buf_ehdr->e_machine);
        ehdr->e_version   = elf32_to_cpu(ehdr, buf_ehdr->e_version);
        ehdr->e_flags     = elf32_to_cpu(ehdr, buf_ehdr->e_flags);
        ehdr->e_phentsize = elf16_to_cpu(ehdr, buf_ehdr->e_phentsize);
        ehdr->e_phnum     = elf16_to_cpu(ehdr, buf_ehdr->e_phnum);
        ehdr->e_shentsize = elf16_to_cpu(ehdr, buf_ehdr->e_shentsize);
        ehdr->e_shnum     = elf16_to_cpu(ehdr, buf_ehdr->e_shnum);
        ehdr->e_shstrndx  = elf16_to_cpu(ehdr, buf_ehdr->e_shstrndx);

        switch (ehdr->e_ident[EI_CLASS]) {
        case ELFCLASS64:
                ehdr->e_entry = elf64_to_cpu(ehdr, buf_ehdr->e_entry);
                ehdr->e_phoff = elf64_to_cpu(ehdr, buf_ehdr->e_phoff);
                ehdr->e_shoff = elf64_to_cpu(ehdr, buf_ehdr->e_shoff);
                break;

        case ELFCLASS32:
                ehdr->e_entry = elf32_to_cpu(ehdr, buf_ehdr->e_entry);
                ehdr->e_phoff = elf32_to_cpu(ehdr, buf_ehdr->e_phoff);
                ehdr->e_shoff = elf32_to_cpu(ehdr, buf_ehdr->e_shoff);
                break;

        default:
                pr_debug("Unknown ELF class.\n");
                return -EINVAL;
        }

        return elf_is_ehdr_sane(ehdr, len) ? 0 : -ENOEXEC;
}

/**
 * elf_is_phdr_sane - check that it is safe to use the program header
 * @buf_len:    size of the buffer in which the ELF file is loaded.
 */
static bool elf_is_phdr_sane(const struct elf_phdr *phdr, size_t buf_len)
{

        if (phdr->p_offset + phdr->p_filesz < phdr->p_offset) {
                pr_debug("ELF segment location wraps around.\n");
                return false;
        } else if (phdr->p_offset + phdr->p_filesz > buf_len) {
                pr_debug("ELF segment not in file.\n");
                return false;
        } else if (phdr->p_paddr + phdr->p_memsz < phdr->p_paddr) {
                pr_debug("ELF segment address wraps around.\n");
                return false;
        }

        return true;
}

static int elf_read_phdr(const char *buf, size_t len,
                         struct kexec_elf_info *elf_info,
                         int idx)
{
        /* Override the const in proghdrs, we are the ones doing the loading. */
        struct elf_phdr *phdr = (struct elf_phdr *) &elf_info->proghdrs[idx];
        const struct elfhdr *ehdr = elf_info->ehdr;
        const char *pbuf;
        struct elf_phdr *buf_phdr;

        pbuf = buf + elf_info->ehdr->e_phoff + (idx * sizeof(*buf_phdr));
        buf_phdr = (struct elf_phdr *) pbuf;

        phdr->p_type   = elf32_to_cpu(elf_info->ehdr, buf_phdr->p_type);
        phdr->p_flags  = elf32_to_cpu(elf_info->ehdr, buf_phdr->p_flags);

        switch (ehdr->e_ident[EI_CLASS]) {
        case ELFCLASS64:
                phdr->p_offset = elf64_to_cpu(ehdr, buf_phdr->p_offset);
                phdr->p_paddr  = elf64_to_cpu(ehdr, buf_phdr->p_paddr);
                phdr->p_vaddr  = elf64_to_cpu(ehdr, buf_phdr->p_vaddr);
                phdr->p_filesz = elf64_to_cpu(ehdr, buf_phdr->p_filesz);
                phdr->p_memsz  = elf64_to_cpu(ehdr, buf_phdr->p_memsz);
                phdr->p_align  = elf64_to_cpu(ehdr, buf_phdr->p_align);
                break;

        case ELFCLASS32:
                phdr->p_offset = elf32_to_cpu(ehdr, buf_phdr->p_offset);
                phdr->p_paddr  = elf32_to_cpu(ehdr, buf_phdr->p_paddr);
                phdr->p_vaddr  = elf32_to_cpu(ehdr, buf_phdr->p_vaddr);
                phdr->p_filesz = elf32_to_cpu(ehdr, buf_phdr->p_filesz);
                phdr->p_memsz  = elf32_to_cpu(ehdr, buf_phdr->p_memsz);
                phdr->p_align  = elf32_to_cpu(ehdr, buf_phdr->p_align);
                break;

        default:
                pr_debug("Unknown ELF class.\n");
                return -EINVAL;
        }

        return elf_is_phdr_sane(phdr, len) ? 0 : -ENOEXEC;
}

/**
 * elf_read_phdrs - read the program headers from the buffer
 *
 * This function assumes that the program header table was checked for sanity.
 * Use elf_is_ehdr_sane() if it wasn't.
 */
static int elf_read_phdrs(const char *buf, size_t len,
                          struct kexec_elf_info *elf_info)
{
        size_t phdr_size, i;
        const struct elfhdr *ehdr = elf_info->ehdr;

        /*
         * e_phnum is at most 65535 so calculating the size of the
         * program header cannot overflow.
         */
        phdr_size = sizeof(struct elf_phdr) * ehdr->e_phnum;

        elf_info->proghdrs = kzalloc(phdr_size, GFP_KERNEL);
        if (!elf_info->proghdrs)
                return -ENOMEM;

        for (i = 0; i < ehdr->e_phnum; i++) {
                int ret;

                ret = elf_read_phdr(buf, len, elf_info, i);
                if (ret) {
                        kfree(elf_info->proghdrs);
                        elf_info->proghdrs = NULL;
                        return ret;
                }
        }

        return 0;
}

/**
 * elf_read_from_buffer - read ELF file and sets up ELF header and ELF info
 * @buf:        Buffer to read ELF file from.
 * @len:        Size of @buf.
 * @ehdr:       Pointer to existing struct which will be populated.
 * @elf_info:   Pointer to existing struct which will be populated.
 *
 * This function allows reading ELF files with different byte order than
 * the kernel, byte-swapping the fields as needed.
 *
 * Return:
 * On success returns 0, and the caller should call
 * kexec_free_elf_info(elf_info) to free the memory allocated for the section
 * and program headers.
 */
static int elf_read_from_buffer(const char *buf, size_t len,
                                struct elfhdr *ehdr,
                                struct kexec_elf_info *elf_info)
{
        int ret;

        ret = elf_read_ehdr(buf, len, ehdr);
        if (ret)
                return ret;

        elf_info->buffer = buf;
        elf_info->ehdr = ehdr;
        if (ehdr->e_phoff > 0 && ehdr->e_phnum > 0) {
                ret = elf_read_phdrs(buf, len, elf_info);
                if (ret)
                        return ret;
        }
        return 0;
}

/**
 * kexec_free_elf_info - free memory allocated by elf_read_from_buffer
 */
void kexec_free_elf_info(struct kexec_elf_info *elf_info)
{
        kfree(elf_info->proghdrs);
        memset(elf_info, 0, sizeof(*elf_info));
}
/**
 * kexec_build_elf_info - read ELF executable and check that we can use it
 */
int kexec_build_elf_info(const char *buf, size_t len, struct elfhdr *ehdr,
                               struct kexec_elf_info *elf_info)
{
        int i;
        int ret;

        ret = elf_read_from_buffer(buf, len, ehdr, elf_info);
        if (ret)
                return ret;

        /* Big endian vmlinux has type ET_DYN. */
        if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) {
                pr_err("Not an ELF executable.\n");
                goto error;
        } else if (!elf_info->proghdrs) {
                pr_err("No ELF program header.\n");
                goto error;
        }

        for (i = 0; i < ehdr->e_phnum; i++) {
                /*
                 * Kexec does not support loading interpreters.
                 * In addition this check keeps us from attempting
                 * to kexec ordinay executables.
                 */
                if (elf_info->proghdrs[i].p_type == PT_INTERP) {
                        pr_err("Requires an ELF interpreter.\n");
                        goto error;
                }
        }

        return 0;
error:
        kexec_free_elf_info(elf_info);
        return -ENOEXEC;
}


int kexec_elf_probe(const char *buf, unsigned long len)
{
        struct elfhdr ehdr;
        struct kexec_elf_info elf_info;
        int ret;

        ret = kexec_build_elf_info(buf, len, &ehdr, &elf_info);
        if (ret)
                return ret;

        kexec_free_elf_info(&elf_info);

        return elf_check_arch(&ehdr) ? 0 : -ENOEXEC;
}

/**
 * kexec_elf_load - load ELF executable image
 * @lowest_load_addr:   On return, will be the address where the first PT_LOAD
 *                      section will be loaded in memory.
 *
 * Return:
 * 0 on success, negative value on failure.
 */
int kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
                         struct kexec_elf_info *elf_info,
                         struct kexec_buf *kbuf,
                         unsigned long *lowest_load_addr)
{
        unsigned long lowest_addr = UINT_MAX;
        int ret;
        size_t i;

        /* Read in the PT_LOAD segments. */
        for (i = 0; i < ehdr->e_phnum; i++) {
                unsigned long load_addr;
                size_t size;
                const struct elf_phdr *phdr;

                phdr = &elf_info->proghdrs[i];
                if (phdr->p_type != PT_LOAD)
                        continue;

                size = phdr->p_filesz;
                if (size > phdr->p_memsz)
                        size = phdr->p_memsz;

                kbuf->buffer = (void *) elf_info->buffer + phdr->p_offset;
                kbuf->bufsz = size;
                kbuf->memsz = phdr->p_memsz;
                kbuf->buf_align = phdr->p_align;
                kbuf->buf_min = phdr->p_paddr;
                kbuf->mem = KEXEC_BUF_MEM_UNKNOWN;
                ret = kexec_add_buffer(kbuf);
                if (ret)
                        goto out;
                load_addr = kbuf->mem;

                if (load_addr < lowest_addr)
                        lowest_addr = load_addr;
        }

        *lowest_load_addr = lowest_addr;
        ret = 0;
 out:
        return ret;
}