xref: /linux-6.15/arch/arm/kernel/module.c (revision 9b69b52c)

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/kernel/module.c
 *
 *  Copyright (C) 2002 Russell King.
 *  Modified for nommu by Hyok S. Choi
 *
 * Module allocation method suggested by Andi Kleen.
 */
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/elf.h>
#include <linux/fs.h>
#include <linux/string.h>

#include <asm/sections.h>
#include <asm/smp_plat.h>
#include <asm/unwind.h>
#include <asm/opcodes.h>

bool module_init_section(const char *name)
{
	return strstarts(name, ".init") ||
		strstarts(name, ".ARM.extab.init") ||
		strstarts(name, ".ARM.exidx.init");
}

bool module_exit_section(const char *name)
{
	return strstarts(name, ".exit") ||
		strstarts(name, ".ARM.extab.exit") ||
		strstarts(name, ".ARM.exidx.exit");
}

#ifdef CONFIG_ARM_HAS_GROUP_RELOCS
/*
 * This implements the partitioning algorithm for group relocations as
 * documented in the ARM AArch32 ELF psABI (IHI 0044).
 *
 * A single PC-relative symbol reference is divided in up to 3 add or subtract
 * operations, where the final one could be incorporated into a load/store
 * instruction with immediate offset. E.g.,
 *
 *   ADD	Rd, PC, #...		or	ADD	Rd, PC, #...
 *   ADD	Rd, Rd, #...			ADD	Rd, Rd, #...
 *   LDR	Rd, [Rd, #...]			ADD	Rd, Rd, #...
 *
 * The latter has a guaranteed range of only 16 MiB (3x8 == 24 bits), so it is
 * of limited use in the kernel. However, the ADD/ADD/LDR combo has a range of
 * -/+ 256 MiB, (2x8 + 12 == 28 bits), which means it has sufficient range for
 * any in-kernel symbol reference (unless module PLTs are being used).
 *
 * The main advantage of this approach over the typical pattern using a literal
 * load is that literal loads may miss in the D-cache, and generally lead to
 * lower cache efficiency for variables that are referenced often from many
 * different places in the code.
 */
static u32 get_group_rem(u32 group, u32 *offset)
{
	u32 val = *offset;
	u32 shift;
	do {
		shift = val ? (31 - __fls(val)) & ~1 : 32;
		*offset = val;
		if (!val)
			break;
		val &= 0xffffff >> shift;
	} while (group--);
	return shift;
}
#endif

int
apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
	       unsigned int relindex, struct module *module)
{
	Elf32_Shdr *symsec = sechdrs + symindex;
	Elf32_Shdr *relsec = sechdrs + relindex;
	Elf32_Shdr *dstsec = sechdrs + relsec->sh_info;
	Elf32_Rel *rel = (void *)relsec->sh_addr;
	unsigned int i;

	for (i = 0; i < relsec->sh_size / sizeof(Elf32_Rel); i++, rel++) {
		unsigned long loc;
		Elf32_Sym *sym;
		const char *symname;
#ifdef CONFIG_ARM_HAS_GROUP_RELOCS
		u32 shift, group = 1;
#endif
		s32 offset;
		u32 tmp;
#ifdef CONFIG_THUMB2_KERNEL
		u32 upper, lower, sign, j1, j2;
#endif

		offset = ELF32_R_SYM(rel->r_info);
		if (offset < 0 || offset > (symsec->sh_size / sizeof(Elf32_Sym))) {
			pr_err("%s: section %u reloc %u: bad relocation sym offset\n",
				module->name, relindex, i);
			return -ENOEXEC;
		}

		sym = ((Elf32_Sym *)symsec->sh_addr) + offset;
		symname = strtab + sym->st_name;

		if (rel->r_offset < 0 || rel->r_offset > dstsec->sh_size - sizeof(u32)) {
			pr_err("%s: section %u reloc %u sym '%s': out of bounds relocation, offset %d size %u\n",
			       module->name, relindex, i, symname,
			       rel->r_offset, dstsec->sh_size);
			return -ENOEXEC;
		}

		loc = dstsec->sh_addr + rel->r_offset;

		switch (ELF32_R_TYPE(rel->r_info)) {
		case R_ARM_NONE:
			/* ignore */
			break;

		case R_ARM_ABS32:
		case R_ARM_TARGET1:
			*(u32 *)loc += sym->st_value;
			break;

		case R_ARM_PC24:
		case R_ARM_CALL:
		case R_ARM_JUMP24:
			if (sym->st_value & 3) {
				pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (ARM -> Thumb)\n",
				       module->name, relindex, i, symname);
				return -ENOEXEC;
			}

			offset = __mem_to_opcode_arm(*(u32 *)loc);
			offset = (offset & 0x00ffffff) << 2;
			offset = sign_extend32(offset, 25);

			offset += sym->st_value - loc;

			/*
			 * Route through a PLT entry if 'offset' exceeds the
			 * supported range. Note that 'offset + loc + 8'
			 * contains the absolute jump target, i.e.,
			 * @sym + addend, corrected for the +8 PC bias.
			 */
			if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
			    (offset <= (s32)0xfe000000 ||
			     offset >= (s32)0x02000000))
				offset = get_module_plt(module, loc,
							offset + loc + 8)
					 - loc - 8;

			if (offset <= (s32)0xfe000000 ||
			    offset >= (s32)0x02000000) {
				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
				       module->name, relindex, i, symname,
				       ELF32_R_TYPE(rel->r_info), loc,
				       sym->st_value);
				return -ENOEXEC;
			}

			offset >>= 2;
			offset &= 0x00ffffff;

			*(u32 *)loc &= __opcode_to_mem_arm(0xff000000);
			*(u32 *)loc |= __opcode_to_mem_arm(offset);
			break;

	       case R_ARM_V4BX:
		       /* Preserve Rm and the condition code. Alter
			* other bits to re-code instruction as
			* MOV PC,Rm.
			*/
		       *(u32 *)loc &= __opcode_to_mem_arm(0xf000000f);
		       *(u32 *)loc |= __opcode_to_mem_arm(0x01a0f000);
		       break;

		case R_ARM_PREL31:
			offset = (*(s32 *)loc << 1) >> 1; /* sign extend */
			offset += sym->st_value - loc;
			if (offset >= 0x40000000 || offset < -0x40000000) {
				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
				       module->name, relindex, i, symname,
				       ELF32_R_TYPE(rel->r_info), loc,
				       sym->st_value);
				return -ENOEXEC;
			}
			*(u32 *)loc &= 0x80000000;
			*(u32 *)loc |= offset & 0x7fffffff;
			break;

		case R_ARM_REL32:
			*(u32 *)loc += sym->st_value - loc;
			break;

		case R_ARM_MOVW_ABS_NC:
		case R_ARM_MOVT_ABS:
		case R_ARM_MOVW_PREL_NC:
		case R_ARM_MOVT_PREL:
			offset = tmp = __mem_to_opcode_arm(*(u32 *)loc);
			offset = ((offset & 0xf0000) >> 4) | (offset & 0xfff);
			offset = sign_extend32(offset, 15);

			offset += sym->st_value;
			if (ELF32_R_TYPE(rel->r_info) == R_ARM_MOVT_PREL ||
			    ELF32_R_TYPE(rel->r_info) == R_ARM_MOVW_PREL_NC)
				offset -= loc;
			if (ELF32_R_TYPE(rel->r_info) == R_ARM_MOVT_ABS ||
			    ELF32_R_TYPE(rel->r_info) == R_ARM_MOVT_PREL)
				offset >>= 16;

			tmp &= 0xfff0f000;
			tmp |= ((offset & 0xf000) << 4) |
				(offset & 0x0fff);

			*(u32 *)loc = __opcode_to_mem_arm(tmp);
			break;

#ifdef CONFIG_ARM_HAS_GROUP_RELOCS
		case R_ARM_ALU_PC_G0_NC:
			group = 0;
			fallthrough;
		case R_ARM_ALU_PC_G1_NC:
			tmp = __mem_to_opcode_arm(*(u32 *)loc);
			offset = ror32(tmp & 0xff, (tmp & 0xf00) >> 7);
			if (tmp & BIT(22))
				offset = -offset;
			offset += sym->st_value - loc;
			if (offset < 0) {
				offset = -offset;
				tmp = (tmp & ~BIT(23)) | BIT(22); // SUB opcode
			} else {
				tmp = (tmp & ~BIT(22)) | BIT(23); // ADD opcode
			}

			shift = get_group_rem(group, &offset);
			if (shift < 24) {
				offset >>= 24 - shift;
				offset |= (shift + 8) << 7;
			}
			*(u32 *)loc = __opcode_to_mem_arm((tmp & ~0xfff) | offset);
			break;

		case R_ARM_LDR_PC_G2:
			tmp = __mem_to_opcode_arm(*(u32 *)loc);
			offset = tmp & 0xfff;
			if (~tmp & BIT(23))		// U bit cleared?
				offset = -offset;
			offset += sym->st_value - loc;
			if (offset < 0) {
				offset = -offset;
				tmp &= ~BIT(23);	// clear U bit
			} else {
				tmp |= BIT(23);		// set U bit
			}
			get_group_rem(2, &offset);

			if (offset > 0xfff) {
				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
				       module->name, relindex, i, symname,
				       ELF32_R_TYPE(rel->r_info), loc,
				       sym->st_value);
				return -ENOEXEC;
			}
			*(u32 *)loc = __opcode_to_mem_arm((tmp & ~0xfff) | offset);
			break;
#endif
#ifdef CONFIG_THUMB2_KERNEL
		case R_ARM_THM_CALL:
		case R_ARM_THM_JUMP24:
			/*
			 * For function symbols, only Thumb addresses are
			 * allowed (no interworking).
			 *
			 * For non-function symbols, the destination
			 * has no specific ARM/Thumb disposition, so
			 * the branch is resolved under the assumption
			 * that interworking is not required.
			 */
			if (ELF32_ST_TYPE(sym->st_info) == STT_FUNC &&
			    !(sym->st_value & 1)) {
				pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (Thumb -> ARM)\n",
				       module->name, relindex, i, symname);
				return -ENOEXEC;
			}

			upper = __mem_to_opcode_thumb16(*(u16 *)loc);
			lower = __mem_to_opcode_thumb16(*(u16 *)(loc + 2));

			/*
			 * 25 bit signed address range (Thumb-2 BL and B.W
			 * instructions):
			 *   S:I1:I2:imm10:imm11:0
			 * where:
			 *   S     = upper[10]   = offset[24]
			 *   I1    = ~(J1 ^ S)   = offset[23]
			 *   I2    = ~(J2 ^ S)   = offset[22]
			 *   imm10 = upper[9:0]  = offset[21:12]
			 *   imm11 = lower[10:0] = offset[11:1]
			 *   J1    = lower[13]
			 *   J2    = lower[11]
			 */
			sign = (upper >> 10) & 1;
			j1 = (lower >> 13) & 1;
			j2 = (lower >> 11) & 1;
			offset = (sign << 24) | ((~(j1 ^ sign) & 1) << 23) |
				((~(j2 ^ sign) & 1) << 22) |
				((upper & 0x03ff) << 12) |
				((lower & 0x07ff) << 1);
			offset = sign_extend32(offset, 24);
			offset += sym->st_value - loc;

			/*
			 * Route through a PLT entry if 'offset' exceeds the
			 * supported range.
			 */
			if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
			    (offset <= (s32)0xff000000 ||
			     offset >= (s32)0x01000000))
				offset = get_module_plt(module, loc,
							offset + loc + 4)
					 - loc - 4;

			if (offset <= (s32)0xff000000 ||
			    offset >= (s32)0x01000000) {
				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
				       module->name, relindex, i, symname,
				       ELF32_R_TYPE(rel->r_info), loc,
				       sym->st_value);
				return -ENOEXEC;
			}

			sign = (offset >> 24) & 1;
			j1 = sign ^ (~(offset >> 23) & 1);
			j2 = sign ^ (~(offset >> 22) & 1);
			upper = (u16)((upper & 0xf800) | (sign << 10) |
					    ((offset >> 12) & 0x03ff));
			lower = (u16)((lower & 0xd000) |
				      (j1 << 13) | (j2 << 11) |
				      ((offset >> 1) & 0x07ff));

			*(u16 *)loc = __opcode_to_mem_thumb16(upper);
			*(u16 *)(loc + 2) = __opcode_to_mem_thumb16(lower);
			break;

		case R_ARM_THM_MOVW_ABS_NC:
		case R_ARM_THM_MOVT_ABS:
		case R_ARM_THM_MOVW_PREL_NC:
		case R_ARM_THM_MOVT_PREL:
			upper = __mem_to_opcode_thumb16(*(u16 *)loc);
			lower = __mem_to_opcode_thumb16(*(u16 *)(loc + 2));

			/*
			 * MOVT/MOVW instructions encoding in Thumb-2:
			 *
			 * i	= upper[10]
			 * imm4	= upper[3:0]
			 * imm3	= lower[14:12]
			 * imm8	= lower[7:0]
			 *
			 * imm16 = imm4:i:imm3:imm8
			 */
			offset = ((upper & 0x000f) << 12) |
				((upper & 0x0400) << 1) |
				((lower & 0x7000) >> 4) | (lower & 0x00ff);
			offset = sign_extend32(offset, 15);
			offset += sym->st_value;

			if (ELF32_R_TYPE(rel->r_info) == R_ARM_THM_MOVT_PREL ||
			    ELF32_R_TYPE(rel->r_info) == R_ARM_THM_MOVW_PREL_NC)
				offset -= loc;
			if (ELF32_R_TYPE(rel->r_info) == R_ARM_THM_MOVT_ABS ||
			    ELF32_R_TYPE(rel->r_info) == R_ARM_THM_MOVT_PREL)
				offset >>= 16;

			upper = (u16)((upper & 0xfbf0) |
				      ((offset & 0xf000) >> 12) |
				      ((offset & 0x0800) >> 1));
			lower = (u16)((lower & 0x8f00) |
				      ((offset & 0x0700) << 4) |
				      (offset & 0x00ff));
			*(u16 *)loc = __opcode_to_mem_thumb16(upper);
			*(u16 *)(loc + 2) = __opcode_to_mem_thumb16(lower);
			break;
#endif

		default:
			pr_err("%s: unknown relocation: %u\n",
			       module->name, ELF32_R_TYPE(rel->r_info));
			return -ENOEXEC;
		}
	}
	return 0;
}

static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr,
	const Elf_Shdr *sechdrs, const char *name)
{
	const Elf_Shdr *s, *se;
	const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

	for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++)
		if (strcmp(name, secstrs + s->sh_name) == 0)
			return s;

	return NULL;
}

extern void fixup_pv_table(const void *, unsigned long);
extern void fixup_smp(const void *, unsigned long);

int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
		    struct module *mod)
{
	const Elf_Shdr *s = NULL;
#ifdef CONFIG_ARM_UNWIND
	const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
	const Elf_Shdr *sechdrs_end = sechdrs + hdr->e_shnum;
	struct list_head *unwind_list = &mod->arch.unwind_list;

	INIT_LIST_HEAD(unwind_list);
	mod->arch.init_table = NULL;

	for (s = sechdrs; s < sechdrs_end; s++) {
		const char *secname = secstrs + s->sh_name;
		const char *txtname;
		const Elf_Shdr *txt_sec;

		if (!(s->sh_flags & SHF_ALLOC) ||
		    s->sh_type != ELF_SECTION_UNWIND)
			continue;

		if (!strcmp(".ARM.exidx", secname))
			txtname = ".text";
		else
			txtname = secname + strlen(".ARM.exidx");
		txt_sec = find_mod_section(hdr, sechdrs, txtname);

		if (txt_sec) {
			struct unwind_table *table =
				unwind_table_add(s->sh_addr,
						s->sh_size,
						txt_sec->sh_addr,
						txt_sec->sh_size);

			list_add(&table->mod_list, unwind_list);

			/* save init table for module_arch_freeing_init */
			if (strcmp(".ARM.exidx.init.text", secname) == 0)
				mod->arch.init_table = table;
		}
	}
#endif
#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
	s = find_mod_section(hdr, sechdrs, ".pv_table");
	if (s)
		fixup_pv_table((void *)s->sh_addr, s->sh_size);
#endif
	s = find_mod_section(hdr, sechdrs, ".alt.smp.init");
	if (s && !is_smp())
#ifdef CONFIG_SMP_ON_UP
		fixup_smp((void *)s->sh_addr, s->sh_size);
#else
		return -EINVAL;
#endif
	return 0;
}

void
module_arch_cleanup(struct module *mod)
{
#ifdef CONFIG_ARM_UNWIND
	struct unwind_table *tmp;
	struct unwind_table *n;

	list_for_each_entry_safe(tmp, n,
			&mod->arch.unwind_list, mod_list) {
		list_del(&tmp->mod_list);
		unwind_table_del(tmp);
	}
	mod->arch.init_table = NULL;
#endif
}

void __weak module_arch_freeing_init(struct module *mod)
{
#ifdef CONFIG_ARM_UNWIND
	struct unwind_table *init = mod->arch.init_table;

	if (init) {
		mod->arch.init_table = NULL;
		list_del(&init->mod_list);
		unwind_table_del(init);
	}
#endif
}