arch/riscv/kernel/elf_kexec.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Load ELF vmlinux file for the kexec_file_load syscall.
 *
 * Copyright (C) 2021 Huawei Technologies Co, Ltd.
 *
 * Author: Liao Chang (liaochang1@huawei.com)
 *
 * Based on kexec-tools' kexec-elf-riscv.c, heavily modified
 * for kernel.
 */

#define pr_fmt(fmt)	"kexec_image: " fmt

#include <linux/elf.h>
#include <linux/kexec.h>
#include <linux/slab.h>
#include <linux/of.h>
#include <linux/libfdt.h>
#include <linux/types.h>
#include <linux/memblock.h>
#include <asm/setup.h>

static int riscv_kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
				struct kexec_elf_info *elf_info, unsigned long old_pbase,
				unsigned long new_pbase)
{
	int i;
	int ret = 0;
	size_t size;
	struct kexec_buf kbuf;
	const struct elf_phdr *phdr;

	kbuf.image = image;

	for (i = 0; i < ehdr->e_phnum; i++) {
		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.buf_align = phdr->p_align;
		kbuf.mem = phdr->p_paddr - old_pbase + new_pbase;
		kbuf.memsz = phdr->p_memsz;
		kbuf.top_down = false;
		ret = kexec_add_buffer(&kbuf);
		if (ret)
			break;
	}

	return ret;
}

/*
 * Go through the available phsyical memory regions and find one that hold
 * an image of the specified size.
 */
static int elf_find_pbase(struct kimage *image, unsigned long kernel_len,
			  struct elfhdr *ehdr, struct kexec_elf_info *elf_info,
			  unsigned long *old_pbase, unsigned long *new_pbase)
{
	int i;
	int ret;
	struct kexec_buf kbuf;
	const struct elf_phdr *phdr;
	unsigned long lowest_paddr = ULONG_MAX;
	unsigned long lowest_vaddr = ULONG_MAX;

	for (i = 0; i < ehdr->e_phnum; i++) {
		phdr = &elf_info->proghdrs[i];
		if (phdr->p_type != PT_LOAD)
			continue;

		if (lowest_paddr > phdr->p_paddr)
			lowest_paddr = phdr->p_paddr;

		if (lowest_vaddr > phdr->p_vaddr)
			lowest_vaddr = phdr->p_vaddr;
	}

	kbuf.image = image;
	kbuf.buf_min = lowest_paddr;
	kbuf.buf_max = ULONG_MAX;
	kbuf.buf_align = PAGE_SIZE;
	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
	kbuf.memsz = ALIGN(kernel_len, PAGE_SIZE);
	kbuf.top_down = false;
	ret = arch_kexec_locate_mem_hole(&kbuf);
	if (!ret) {
		*old_pbase = lowest_paddr;
		*new_pbase = kbuf.mem;
		image->start = ehdr->e_entry - lowest_vaddr + kbuf.mem;
	}
	return ret;
}

static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
{
	unsigned int *nr_ranges = arg;

	(*nr_ranges)++;
	return 0;
}

static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
{
	struct crash_mem *cmem = arg;

	cmem->ranges[cmem->nr_ranges].start = res->start;
	cmem->ranges[cmem->nr_ranges].end = res->end;
	cmem->nr_ranges++;

	return 0;
}

static int prepare_elf_headers(void **addr, unsigned long *sz)
{
	struct crash_mem *cmem;
	unsigned int nr_ranges;
	int ret;

	nr_ranges = 1; /* For exclusion of crashkernel region */
	walk_system_ram_res(0, -1, &nr_ranges, get_nr_ram_ranges_callback);

	cmem = kmalloc(struct_size(cmem, ranges, nr_ranges), GFP_KERNEL);
	if (!cmem)
		return -ENOMEM;

	cmem->max_nr_ranges = nr_ranges;
	cmem->nr_ranges = 0;
	ret = walk_system_ram_res(0, -1, cmem, prepare_elf64_ram_headers_callback);
	if (ret)
		goto out;

	/* Exclude crashkernel region */
	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
	if (!ret)
		ret = crash_prepare_elf64_headers(cmem, true, addr, sz);

out:
	kfree(cmem);
	return ret;
}

static char *setup_kdump_cmdline(struct kimage *image, char *cmdline,
				 unsigned long cmdline_len)
{
	int elfcorehdr_strlen;
	char *cmdline_ptr;

	cmdline_ptr = kzalloc(COMMAND_LINE_SIZE, GFP_KERNEL);
	if (!cmdline_ptr)
		return NULL;

	elfcorehdr_strlen = sprintf(cmdline_ptr, "elfcorehdr=0x%lx ",
		image->elf_load_addr);

	if (elfcorehdr_strlen + cmdline_len > COMMAND_LINE_SIZE) {
		pr_err("Appending elfcorehdr=<addr> exceeds cmdline size\n");
		kfree(cmdline_ptr);
		return NULL;
	}

	memcpy(cmdline_ptr + elfcorehdr_strlen, cmdline, cmdline_len);
	/* Ensure it's nul terminated */
	cmdline_ptr[COMMAND_LINE_SIZE - 1] = '\0';
	return cmdline_ptr;
}

static void *elf_kexec_load(struct kimage *image, char *kernel_buf,
			    unsigned long kernel_len, char *initrd,
			    unsigned long initrd_len, char *cmdline,
			    unsigned long cmdline_len)
{
	int ret;
	unsigned long old_kernel_pbase = ULONG_MAX;
	unsigned long new_kernel_pbase = 0UL;
	unsigned long initrd_pbase = 0UL;
	unsigned long headers_sz;
	unsigned long kernel_start;
	void *fdt, *headers;
	struct elfhdr ehdr;
	struct kexec_buf kbuf;
	struct kexec_elf_info elf_info;
	char *modified_cmdline = NULL;

	ret = kexec_build_elf_info(kernel_buf, kernel_len, &ehdr, &elf_info);
	if (ret)
		return ERR_PTR(ret);

	ret = elf_find_pbase(image, kernel_len, &ehdr, &elf_info,
			     &old_kernel_pbase, &new_kernel_pbase);
	if (ret)
		goto out;
	kernel_start = image->start;
	pr_notice("The entry point of kernel at 0x%lx\n", image->start);

	/* Add the kernel binary to the image */
	ret = riscv_kexec_elf_load(image, &ehdr, &elf_info,
				   old_kernel_pbase, new_kernel_pbase);
	if (ret)
		goto out;

	kbuf.image = image;
	kbuf.buf_min = new_kernel_pbase + kernel_len;
	kbuf.buf_max = ULONG_MAX;

	/* Add elfcorehdr */
	if (image->type == KEXEC_TYPE_CRASH) {
		ret = prepare_elf_headers(&headers, &headers_sz);
		if (ret) {
			pr_err("Preparing elf core header failed\n");
			goto out;
		}

		kbuf.buffer = headers;
		kbuf.bufsz = headers_sz;
		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
		kbuf.memsz = headers_sz;
		kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
		kbuf.top_down = true;

		ret = kexec_add_buffer(&kbuf);
		if (ret) {
			vfree(headers);
			goto out;
		}
		image->elf_headers = headers;
		image->elf_load_addr = kbuf.mem;
		image->elf_headers_sz = headers_sz;

		pr_debug("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
			 image->elf_load_addr, kbuf.bufsz, kbuf.memsz);

		/* Setup cmdline for kdump kernel case */
		modified_cmdline = setup_kdump_cmdline(image, cmdline,
						       cmdline_len);
		if (!modified_cmdline) {
			pr_err("Setting up cmdline for kdump kernel failed\n");
			ret = -EINVAL;
			goto out;
		}
		cmdline = modified_cmdline;
	}

#ifdef CONFIG_ARCH_HAS_KEXEC_PURGATORY
	/* Add purgatory to the image */
	kbuf.top_down = true;
	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
	ret = kexec_load_purgatory(image, &kbuf);
	if (ret) {
		pr_err("Error loading purgatory ret=%d\n", ret);
		goto out;
	}
	ret = kexec_purgatory_get_set_symbol(image, "riscv_kernel_entry",
					     &kernel_start,
					     sizeof(kernel_start), 0);
	if (ret)
		pr_err("Error update purgatory ret=%d\n", ret);
#endif /* CONFIG_ARCH_HAS_KEXEC_PURGATORY */

	/* Add the initrd to the image */
	if (initrd != NULL) {
		kbuf.buffer = initrd;
		kbuf.bufsz = kbuf.memsz = initrd_len;
		kbuf.buf_align = PAGE_SIZE;
		kbuf.top_down = false;
		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
		ret = kexec_add_buffer(&kbuf);
		if (ret)
			goto out;
		initrd_pbase = kbuf.mem;
		pr_notice("Loaded initrd at 0x%lx\n", initrd_pbase);
	}

	/* Add the DTB to the image */
	fdt = of_kexec_alloc_and_setup_fdt(image, initrd_pbase,
					   initrd_len, cmdline, 0);
	if (!fdt) {
		pr_err("Error setting up the new device tree.\n");
		ret = -EINVAL;
		goto out;
	}

	fdt_pack(fdt);
	kbuf.buffer = fdt;
	kbuf.bufsz = kbuf.memsz = fdt_totalsize(fdt);
	kbuf.buf_align = PAGE_SIZE;
	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
	kbuf.top_down = true;
	ret = kexec_add_buffer(&kbuf);
	if (ret) {
		pr_err("Error add DTB kbuf ret=%d\n", ret);
		goto out_free_fdt;
	}
	pr_notice("Loaded device tree at 0x%lx\n", kbuf.mem);
	goto out;

out_free_fdt:
	kvfree(fdt);
out:
	kfree(modified_cmdline);
	kexec_free_elf_info(&elf_info);
	return ret ? ERR_PTR(ret) : NULL;
}

#define RV_X(x, s, n)  (((x) >> (s)) & ((1 << (n)) - 1))
#define RISCV_IMM_BITS 12
#define RISCV_IMM_REACH (1LL << RISCV_IMM_BITS)
#define RISCV_CONST_HIGH_PART(x) \
	(((x) + (RISCV_IMM_REACH >> 1)) & ~(RISCV_IMM_REACH - 1))
#define RISCV_CONST_LOW_PART(x) ((x) - RISCV_CONST_HIGH_PART(x))

#define ENCODE_ITYPE_IMM(x) \
	(RV_X(x, 0, 12) << 20)
#define ENCODE_BTYPE_IMM(x) \
	((RV_X(x, 1, 4) << 8) | (RV_X(x, 5, 6) << 25) | \
	(RV_X(x, 11, 1) << 7) | (RV_X(x, 12, 1) << 31))
#define ENCODE_UTYPE_IMM(x) \
	(RV_X(x, 12, 20) << 12)
#define ENCODE_JTYPE_IMM(x) \
	((RV_X(x, 1, 10) << 21) | (RV_X(x, 11, 1) << 20) | \
	(RV_X(x, 12, 8) << 12) | (RV_X(x, 20, 1) << 31))
#define ENCODE_CBTYPE_IMM(x) \
	((RV_X(x, 1, 2) << 3) | (RV_X(x, 3, 2) << 10) | (RV_X(x, 5, 1) << 2) | \
	(RV_X(x, 6, 2) << 5) | (RV_X(x, 8, 1) << 12))
#define ENCODE_CJTYPE_IMM(x) \
	((RV_X(x, 1, 3) << 3) | (RV_X(x, 4, 1) << 11) | (RV_X(x, 5, 1) << 2) | \
	(RV_X(x, 6, 1) << 7) | (RV_X(x, 7, 1) << 6) | (RV_X(x, 8, 2) << 9) | \
	(RV_X(x, 10, 1) << 8) | (RV_X(x, 11, 1) << 12))
#define ENCODE_UJTYPE_IMM(x) \
	(ENCODE_UTYPE_IMM(RISCV_CONST_HIGH_PART(x)) | \
	(ENCODE_ITYPE_IMM(RISCV_CONST_LOW_PART(x)) << 32))
#define ENCODE_UITYPE_IMM(x) \
	(ENCODE_UTYPE_IMM(x) | (ENCODE_ITYPE_IMM(x) << 32))

#define CLEAN_IMM(type, x) \
	((~ENCODE_##type##_IMM((uint64_t)(-1))) & (x))

int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
				     Elf_Shdr *section,
				     const Elf_Shdr *relsec,
				     const Elf_Shdr *symtab)
{
	const char *strtab, *name, *shstrtab;
	const Elf_Shdr *sechdrs;
	Elf64_Rela *relas;
	int i, r_type;

	/* String & section header string table */
	sechdrs = (void *)pi->ehdr + pi->ehdr->e_shoff;
	strtab = (char *)pi->ehdr + sechdrs[symtab->sh_link].sh_offset;
	shstrtab = (char *)pi->ehdr + sechdrs[pi->ehdr->e_shstrndx].sh_offset;

	relas = (void *)pi->ehdr + relsec->sh_offset;

	for (i = 0; i < relsec->sh_size / sizeof(*relas); i++) {
		const Elf_Sym *sym;	/* symbol to relocate */
		unsigned long addr;	/* final location after relocation */
		unsigned long val;	/* relocated symbol value */
		unsigned long sec_base;	/* relocated symbol value */
		void *loc;		/* tmp location to modify */

		sym = (void *)pi->ehdr + symtab->sh_offset;
		sym += ELF64_R_SYM(relas[i].r_info);

		if (sym->st_name)
			name = strtab + sym->st_name;
		else
			name = shstrtab + sechdrs[sym->st_shndx].sh_name;

		loc = pi->purgatory_buf;
		loc += section->sh_offset;
		loc += relas[i].r_offset;

		if (sym->st_shndx == SHN_ABS)
			sec_base = 0;
		else if (sym->st_shndx >= pi->ehdr->e_shnum) {
			pr_err("Invalid section %d for symbol %s\n",
			       sym->st_shndx, name);
			return -ENOEXEC;
		} else
			sec_base = pi->sechdrs[sym->st_shndx].sh_addr;

		val = sym->st_value;
		val += sec_base;
		val += relas[i].r_addend;

		addr = section->sh_addr + relas[i].r_offset;

		r_type = ELF64_R_TYPE(relas[i].r_info);

		switch (r_type) {
		case R_RISCV_BRANCH:
			*(u32 *)loc = CLEAN_IMM(BTYPE, *(u32 *)loc) |
				 ENCODE_BTYPE_IMM(val - addr);
			break;
		case R_RISCV_JAL:
			*(u32 *)loc = CLEAN_IMM(JTYPE, *(u32 *)loc) |
				 ENCODE_JTYPE_IMM(val - addr);
			break;
		/*
		 * With no R_RISCV_PCREL_LO12_S, R_RISCV_PCREL_LO12_I
		 * sym is expected to be next to R_RISCV_PCREL_HI20
		 * in purgatory relsec. Handle it like R_RISCV_CALL
		 * sym, instead of searching the whole relsec.
		 */
		case R_RISCV_PCREL_HI20:
		case R_RISCV_CALL:
			*(u64 *)loc = CLEAN_IMM(UITYPE, *(u64 *)loc) |
				 ENCODE_UJTYPE_IMM(val - addr);
			break;
		case R_RISCV_RVC_BRANCH:
			*(u32 *)loc = CLEAN_IMM(CBTYPE, *(u32 *)loc) |
				 ENCODE_CBTYPE_IMM(val - addr);
			break;
		case R_RISCV_RVC_JUMP:
			*(u32 *)loc = CLEAN_IMM(CJTYPE, *(u32 *)loc) |
				 ENCODE_CJTYPE_IMM(val - addr);
			break;
		case R_RISCV_ADD32:
			*(u32 *)loc += val;
			break;
		case R_RISCV_SUB32:
			*(u32 *)loc -= val;
			break;
		/* It has been applied by R_RISCV_PCREL_HI20 sym */
		case R_RISCV_PCREL_LO12_I:
		case R_RISCV_ALIGN:
		case R_RISCV_RELAX:
			break;
		default:
			pr_err("Unknown rela relocation: %d\n", r_type);
			return -ENOEXEC;
		}
	}
	return 0;
}

const struct kexec_file_ops elf_kexec_ops = {
	.probe = kexec_elf_probe,
	.load  = elf_kexec_load,
};