module-sections.c

/* SPDX-License-Identifier: GPL-2.0
 *
 * Copyright (C) 2014-2017 Linaro Ltd. <[email protected]>
 *
 * Copyright (C) 2018 Andes Technology Corporation <[email protected]>
 */

#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/sort.h>

unsigned long module_emit_got_entry(struct module *mod, unsigned long val)
{
	struct mod_section *got_sec = &mod->arch.got;
	int i = got_sec->num_entries;
	struct got_entry *got = get_got_entry(val, got_sec);

	if (got)
		return (unsigned long)got;

	/* There is no duplicate entry, create a new one */
	got = (struct got_entry *)got_sec->shdr->sh_addr;
	got[i] = emit_got_entry(val);

	got_sec->num_entries++;
	BUG_ON(got_sec->num_entries > got_sec->max_entries);

	return (unsigned long)&got[i];
}

unsigned long module_emit_plt_entry(struct module *mod, unsigned long val)
{
	struct mod_section *got_plt_sec = &mod->arch.got_plt;
	struct got_entry *got_plt;
	struct mod_section *plt_sec = &mod->arch.plt;
	struct plt_entry *plt = get_plt_entry(val, plt_sec, got_plt_sec);
	int i = plt_sec->num_entries;

	if (plt)
		return (unsigned long)plt;

	/* There is no duplicate entry, create a new one */
	got_plt = (struct got_entry *)got_plt_sec->shdr->sh_addr;
	got_plt[i] = emit_got_entry(val);
	plt = (struct plt_entry *)plt_sec->shdr->sh_addr;
	plt[i] = emit_plt_entry(val,
				(unsigned long)&plt[i],
				(unsigned long)&got_plt[i]);

	plt_sec->num_entries++;
	got_plt_sec->num_entries++;
	BUG_ON(plt_sec->num_entries > plt_sec->max_entries);

	return (unsigned long)&plt[i];
}

#define cmp_3way(a, b)	((a) < (b) ? -1 : (a) > (b))

static int cmp_rela(const void *a, const void *b)
{
	const Elf_Rela *x = a, *y = b;
	int i;

	/* sort by type, symbol index and addend */
	i = cmp_3way(x->r_info, y->r_info);
	if (i == 0)
		i = cmp_3way(x->r_addend, y->r_addend);
	return i;
}

static bool duplicate_rela(const Elf_Rela *rela, int idx)
{
	/*
	 * Entries are sorted by type, symbol index and addend. That means
	 * that, if a duplicate entry exists, it must be in the preceding slot.
	 */
	return idx > 0 && cmp_rela(rela + idx, rela + idx - 1) == 0;
}

static void count_max_entries(const Elf_Rela *relas, size_t num,
			      unsigned int *plts, unsigned int *gots)
{
	for (size_t i = 0; i < num; i++) {
		if (duplicate_rela(relas, i))
			continue;

		switch (ELF_R_TYPE(relas[i].r_info)) {
		case R_RISCV_CALL_PLT:
		case R_RISCV_PLT32:
			(*plts)++;
			break;
		case R_RISCV_GOT_HI20:
			(*gots)++;
			break;
		default:
			unreachable();
		}
	}
}

static bool rela_needs_plt_got_entry(const Elf_Rela *rela)
{
	switch (ELF_R_TYPE(rela->r_info)) {
	case R_RISCV_CALL_PLT:
	case R_RISCV_GOT_HI20:
	case R_RISCV_PLT32:
		return true;
	default:
		return false;
	}
}

int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
			      char *secstrings, struct module *mod)
{
	size_t num_scratch_relas = 0;
	unsigned int num_plts = 0;
	unsigned int num_gots = 0;
	Elf_Rela *scratch = NULL;
	Elf_Rela *new_scratch;
	size_t scratch_size = 0;
	int i;

	/*
	 * Find the empty .got and .plt sections.
	 */
	for (i = 0; i < ehdr->e_shnum; i++) {
		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
			mod->arch.plt.shdr = sechdrs + i;
		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
			mod->arch.got.shdr = sechdrs + i;
		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got.plt"))
			mod->arch.got_plt.shdr = sechdrs + i;
	}

	if (!mod->arch.plt.shdr) {
		pr_err("%s: module PLT section(s) missing\n", mod->name);
		return -ENOEXEC;
	}
	if (!mod->arch.got.shdr) {
		pr_err("%s: module GOT section(s) missing\n", mod->name);
		return -ENOEXEC;
	}
	if (!mod->arch.got_plt.shdr) {
		pr_err("%s: module GOT.PLT section(s) missing\n", mod->name);
		return -ENOEXEC;
	}

	/* Calculate the maxinum number of entries */
	for (i = 0; i < ehdr->e_shnum; i++) {
		size_t num_relas = sechdrs[i].sh_size / sizeof(Elf_Rela);
		Elf_Rela *relas = (void *)ehdr + sechdrs[i].sh_offset;
		Elf_Shdr *dst_sec = sechdrs + sechdrs[i].sh_info;
		size_t scratch_size_needed;

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

		/* ignore relocations that operate on non-exec sections */
		if (!(dst_sec->sh_flags & SHF_EXECINSTR))
			continue;

		/*
		 * apply_relocate_add() relies on HI20 and LO12 relocation pairs being
		 * close together, so sort a copy of the section to avoid interfering.
		 */
		scratch_size_needed = (num_scratch_relas + num_relas) * sizeof(*scratch);
		if (scratch_size_needed > scratch_size) {
			scratch_size = scratch_size_needed;
			new_scratch = kvrealloc(scratch, scratch_size, GFP_KERNEL);
			if (!new_scratch) {
				kvfree(scratch);
				return -ENOMEM;
			}
			scratch = new_scratch;
		}

		for (size_t j = 0; j < num_relas; j++)
			if (rela_needs_plt_got_entry(&relas[j]))
				scratch[num_scratch_relas++] = relas[j];
	}

	if (scratch) {
		/* sort the accumulated PLT/GOT relocations so duplicates are adjacent */
		sort(scratch, num_scratch_relas, sizeof(*scratch), cmp_rela, NULL);
		count_max_entries(scratch, num_scratch_relas, &num_plts, &num_gots);
		kvfree(scratch);
	}

	mod->arch.plt.shdr->sh_type = SHT_NOBITS;
	mod->arch.plt.shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
	mod->arch.plt.shdr->sh_addralign = L1_CACHE_BYTES;
	mod->arch.plt.shdr->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
	mod->arch.plt.num_entries = 0;
	mod->arch.plt.max_entries = num_plts;

	mod->arch.got.shdr->sh_type = SHT_NOBITS;
	mod->arch.got.shdr->sh_flags = SHF_ALLOC;
	mod->arch.got.shdr->sh_addralign = L1_CACHE_BYTES;
	mod->arch.got.shdr->sh_size = (num_gots + 1) * sizeof(struct got_entry);
	mod->arch.got.num_entries = 0;
	mod->arch.got.max_entries = num_gots;

	mod->arch.got_plt.shdr->sh_type = SHT_NOBITS;
	mod->arch.got_plt.shdr->sh_flags = SHF_ALLOC;
	mod->arch.got_plt.shdr->sh_addralign = L1_CACHE_BYTES;
	mod->arch.got_plt.shdr->sh_size = (num_plts + 1) * sizeof(struct got_entry);
	mod->arch.got_plt.num_entries = 0;
	mod->arch.got_plt.max_entries = num_plts;
	return 0;
}