module.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*  Kernel module help for x86.
    Copyright (C) 2001 Rusty Russell.

*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/moduleloader.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/kasan.h>
#include <linux/bug.h>
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/jump_label.h>
#include <linux/random.h>
#include <linux/memory.h>

#include <asm/text-patching.h>
#include <asm/page.h>
#include <asm/setup.h>
#include <asm/unwind.h>

#if 0
#define DEBUGP(fmt, ...)				\
	printk(KERN_DEBUG fmt, ##__VA_ARGS__)
#else
#define DEBUGP(fmt, ...)				\
do {							\
	if (0)						\
		printk(KERN_DEBUG fmt, ##__VA_ARGS__);	\
} while (0)
#endif

#ifdef CONFIG_RANDOMIZE_BASE
static unsigned long module_load_offset;

/* Mutex protects the module_load_offset. */
static DEFINE_MUTEX(module_kaslr_mutex);

static unsigned long int get_module_load_offset(void)
{
	if (kaslr_enabled()) {
		mutex_lock(&module_kaslr_mutex);
		/*
		 * Calculate the module_load_offset the first time this
		 * code is called. Once calculated it stays the same until
		 * reboot.
		 */
		if (module_load_offset == 0)
			module_load_offset =
				(prandom_u32_max(1024) + 1) * PAGE_SIZE;
		mutex_unlock(&module_kaslr_mutex);
	}
	return module_load_offset;
}
#else
static unsigned long int get_module_load_offset(void)
{
	return 0;
}
#endif

void *module_alloc(unsigned long size)
{
	gfp_t gfp_mask = GFP_KERNEL;
	void *p;

	if (PAGE_ALIGN(size) > MODULES_LEN)
		return NULL;

	p = __vmalloc_node_range(size, MODULE_ALIGN,
				    MODULES_VADDR + get_module_load_offset(),
				    MODULES_END, gfp_mask,
				    PAGE_KERNEL, VM_DEFER_KMEMLEAK, NUMA_NO_NODE,
				    __builtin_return_address(0));
	if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0)) {
		vfree(p);
		return NULL;
	}

	return p;
}

#ifdef CONFIG_X86_32
int apply_relocate(Elf32_Shdr *sechdrs,
		   const char *strtab,
		   unsigned int symindex,
		   unsigned int relsec,
		   struct module *me)
{
	unsigned int i;
	Elf32_Rel *rel = (void *)sechdrs[relsec].sh_addr;
	Elf32_Sym *sym;
	uint32_t *location;

	DEBUGP("Applying relocate section %u to %u\n",
	       relsec, sechdrs[relsec].sh_info);
	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
		/* This is where to make the change */
		location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
			+ rel[i].r_offset;
		/* This is the symbol it is referring to.  Note that all
		   undefined symbols have been resolved.  */
		sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
			+ ELF32_R_SYM(rel[i].r_info);

		switch (ELF32_R_TYPE(rel[i].r_info)) {
		case R_386_32:
			/* We add the value into the location given */
			*location += sym->st_value;
			break;
		case R_386_PC32:
		case R_386_PLT32:
			/* Add the value, subtract its position */
			*location += sym->st_value - (uint32_t)location;
			break;
		default:
			pr_err("%s: Unknown relocation: %u\n",
			       me->name, ELF32_R_TYPE(rel[i].r_info));
			return -ENOEXEC;
		}
	}
	return 0;
}
#else /*X86_64*/
static int __apply_relocate_add(Elf64_Shdr *sechdrs,
		   const char *strtab,
		   unsigned int symindex,
		   unsigned int relsec,
		   struct module *me,
		   void *(*write)(void *dest, const void *src, size_t len))
{
	unsigned int i;
	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
	Elf64_Sym *sym;
	void *loc;
	u64 val;

	DEBUGP("Applying relocate section %u to %u\n",
	       relsec, sechdrs[relsec].sh_info);
	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
		/* This is where to make the change */
		loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
			+ rel[i].r_offset;

		/* This is the symbol it is referring to.  Note that all
		   undefined symbols have been resolved.  */
		sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
			+ ELF64_R_SYM(rel[i].r_info);

		DEBUGP("type %d st_value %Lx r_addend %Lx loc %Lx\n",
		       (int)ELF64_R_TYPE(rel[i].r_info),
		       sym->st_value, rel[i].r_addend, (u64)loc);

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

		switch (ELF64_R_TYPE(rel[i].r_info)) {
		case R_X86_64_NONE:
			break;
		case R_X86_64_64:
			if (*(u64 *)loc != 0)
				goto invalid_relocation;
			write(loc, &val, 8);
			break;
		case R_X86_64_32:
			if (*(u32 *)loc != 0)
				goto invalid_relocation;
			write(loc, &val, 4);
			if (val != *(u32 *)loc)
				goto overflow;
			break;
		case R_X86_64_32S:
			if (*(s32 *)loc != 0)
				goto invalid_relocation;
			write(loc, &val, 4);
			if ((s64)val != *(s32 *)loc)
				goto overflow;
			break;
		case R_X86_64_PC32:
		case R_X86_64_PLT32:
			if (*(u32 *)loc != 0)
				goto invalid_relocation;
			val -= (u64)loc;
			write(loc, &val, 4);
			break;
		case R_X86_64_PC64:
			if (*(u64 *)loc != 0)
				goto invalid_relocation;
			val -= (u64)loc;
			write(loc, &val, 8);
			break;
		default:
			pr_err("%s: Unknown rela relocation: %llu\n",
			       me->name, ELF64_R_TYPE(rel[i].r_info));
			return -ENOEXEC;
		}
	}
	return 0;

invalid_relocation:
	pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
	       (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
	return -ENOEXEC;

overflow:
	pr_err("overflow in relocation type %d val %Lx\n",
	       (int)ELF64_R_TYPE(rel[i].r_info), val);
	pr_err("`%s' likely not compiled with -mcmodel=kernel\n",
	       me->name);
	return -ENOEXEC;
}

int apply_relocate_add(Elf64_Shdr *sechdrs,
		   const char *strtab,
		   unsigned int symindex,
		   unsigned int relsec,
		   struct module *me)
{
	int ret;
	bool early = me->state == MODULE_STATE_UNFORMED;
	void *(*write)(void *, const void *, size_t) = memcpy;

	if (!early) {
		write = text_poke;
		mutex_lock(&text_mutex);
	}

	ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
				   write);

	if (!early) {
		text_poke_sync();
		mutex_unlock(&text_mutex);
	}

	return ret;
}

#endif

int module_finalize(const Elf_Ehdr *hdr,
		    const Elf_Shdr *sechdrs,
		    struct module *me)
{
	const Elf_Shdr *s, *alt = NULL, *locks = NULL,
		*para = NULL, *orc = NULL, *orc_ip = NULL,
		*retpolines = NULL, *returns = NULL, *ibt_endbr = NULL;
	char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

	for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
		if (!strcmp(".altinstructions", secstrings + s->sh_name))
			alt = s;
		if (!strcmp(".smp_locks", secstrings + s->sh_name))
			locks = s;
		if (!strcmp(".parainstructions", secstrings + s->sh_name))
			para = s;
		if (!strcmp(".orc_unwind", secstrings + s->sh_name))
			orc = s;
		if (!strcmp(".orc_unwind_ip", secstrings + s->sh_name))
			orc_ip = s;
		if (!strcmp(".retpoline_sites", secstrings + s->sh_name))
			retpolines = s;
		if (!strcmp(".return_sites", secstrings + s->sh_name))
			returns = s;
		if (!strcmp(".ibt_endbr_seal", secstrings + s->sh_name))
			ibt_endbr = s;
	}

	/*
	 * See alternative_instructions() for the ordering rules between the
	 * various patching types.
	 */
	if (para) {
		void *pseg = (void *)para->sh_addr;
		apply_paravirt(pseg, pseg + para->sh_size);
	}
	if (retpolines) {
		void *rseg = (void *)retpolines->sh_addr;
		apply_retpolines(rseg, rseg + retpolines->sh_size);
	}
	if (returns) {
		void *rseg = (void *)returns->sh_addr;
		apply_returns(rseg, rseg + returns->sh_size);
	}
	if (alt) {
		/* patch .altinstructions */
		void *aseg = (void *)alt->sh_addr;
		apply_alternatives(aseg, aseg + alt->sh_size);
	}
	if (ibt_endbr) {
		void *iseg = (void *)ibt_endbr->sh_addr;
		apply_ibt_endbr(iseg, iseg + ibt_endbr->sh_size);
	}
	if (locks) {
		void *lseg = (void *)locks->sh_addr;
		void *text = me->core_layout.base;
		void *text_end = text + me->core_layout.text_size;
		alternatives_smp_module_add(me, me->name,
					    lseg, lseg + locks->sh_size,
					    text, text_end);
	}

	if (orc && orc_ip)
		unwind_module_init(me, (void *)orc_ip->sh_addr, orc_ip->sh_size,
				   (void *)orc->sh_addr, orc->sh_size);

	return 0;
}

void module_arch_cleanup(struct module *mod)
{
	alternatives_smp_module_del(mod);
}