arm64: Loadable modules

This patch adds support for loadable modules. Loadable modules are
loaded 64MB below the kernel image due to branch relocation restrictions
(see Documentation/arm64/memory.txt).

Signed-off-by: Will Deacon <[e-mail]>
Signed-off-by: Catalin Marinas <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Acked-by: Nicolas Pitre <[e-mail]>
Acked-by: Olof Johansson <[e-mail]>
Acked-by: Santosh Shilimkar <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>

arch/arm64/include/asm/module.h

···
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __ASM_MODULE_H
+#define __ASM_MODULE_H
+
+#include <asm-generic/module.h>
+
+#define MODULE_ARCH_VERMAGIC	"aarch64"
+
+#endif /* __ASM_MODULE_H */

arch/arm64/kernel/module.c

···
+/*
+ * AArch64 loadable module support.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Will Deacon <[e-mail]>
+ */
+
+#include <linux/bitops.h>
+#include <linux/elf.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/moduleloader.h>
+#include <linux/vmalloc.h>
+
+void *module_alloc(unsigned long size)
+{
+	return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
+				    GFP_KERNEL, PAGE_KERNEL_EXEC, -1,
+				    __builtin_return_address(0));
+}
+
+enum aarch64_reloc_op {
+	RELOC_OP_NONE,
+	RELOC_OP_ABS,
+	RELOC_OP_PREL,
+	RELOC_OP_PAGE,
+};
+
+static u64 do_reloc(enum aarch64_reloc_op reloc_op, void *place, u64 val)
+{
+	switch (reloc_op) {
+	case RELOC_OP_ABS:
+		return val;
+	case RELOC_OP_PREL:
+		return val - (u64)place;
+	case RELOC_OP_PAGE:
+		return (val & ~0xfff) - ((u64)place & ~0xfff);
+	case RELOC_OP_NONE:
+		return 0;
+	}
+
+	pr_err("do_reloc: unknown relocation operation %d\n", reloc_op);
+	return 0;
+}
+
+static int reloc_data(enum aarch64_reloc_op op, void *place, u64 val, int len)
+{
+	u64 imm_mask = (1 << len) - 1;
+	s64 sval = do_reloc(op, place, val);
+
+	switch (len) {
+	case 16:
+		*(s16 *)place = sval;
+		break;
+	case 32:
+		*(s32 *)place = sval;
+		break;
+	case 64:
+		*(s64 *)place = sval;
+		break;
+	default:
+		pr_err("Invalid length (%d) for data relocation\n", len);
+		return 0;
+	}
+
+	/*
+	 * Extract the upper value bits (including the sign bit) and
+	 * shift them to bit 0.
+	 */
+	sval = (s64)(sval & ~(imm_mask >> 1)) >> (len - 1);
+
+	/*
+	 * Overflow has occurred if the value is not representable in
+	 * len bits (i.e the bottom len bits are not sign-extended and
+	 * the top bits are not all zero).
+	 */
+	if ((u64)(sval + 1) > 2)
+		return -ERANGE;
+
+	return 0;
+}
+
+enum aarch64_imm_type {
+	INSN_IMM_MOVNZ,
+	INSN_IMM_MOVK,
+	INSN_IMM_ADR,
+	INSN_IMM_26,
+	INSN_IMM_19,
+	INSN_IMM_16,
+	INSN_IMM_14,
+	INSN_IMM_12,
+	INSN_IMM_9,
+};
+
+static u32 encode_insn_immediate(enum aarch64_imm_type type, u32 insn, u64 imm)
+{
+	u32 immlo, immhi, lomask, himask, mask;
+	int shift;
+
+	switch (type) {
+	case INSN_IMM_MOVNZ:
+		/*
+		 * For signed MOVW relocations, we have to manipulate the
+		 * instruction encoding depending on whether or not the
+		 * immediate is less than zero.
+		 */
+		insn &= ~(3 << 29);
+		if ((s64)imm >= 0) {
+			/* >=0: Set the instruction to MOVZ (opcode 10b). */
+			insn |= 2 << 29;
+		} else {
+			/*
+			 * <0: Set the instruction to MOVN (opcode 00b).
+			 *     Since we've masked the opcode already, we
+			 *     don't need to do anything other than
+			 *     inverting the new immediate field.
+			 */
+			imm = ~imm;
+		}
+	case INSN_IMM_MOVK:
+		mask = BIT(16) - 1;
+		shift = 5;
+		break;
+	case INSN_IMM_ADR:
+		lomask = 0x3;
+		himask = 0x7ffff;
+		immlo = imm & lomask;
+		imm >>= 2;
+		immhi = imm & himask;
+		imm = (immlo << 24) | (immhi);
+		mask = (lomask << 24) | (himask);
+		shift = 5;
+		break;
+	case INSN_IMM_26:
+		mask = BIT(26) - 1;
+		shift = 0;
+		break;
+	case INSN_IMM_19:
+		mask = BIT(19) - 1;
+		shift = 5;
+		break;
+	case INSN_IMM_16:
+		mask = BIT(16) - 1;
+		shift = 5;
+		break;
+	case INSN_IMM_14:
+		mask = BIT(14) - 1;
+		shift = 5;
+		break;
+	case INSN_IMM_12:
+		mask = BIT(12) - 1;
+		shift = 10;
+		break;
+	case INSN_IMM_9:
+		mask = BIT(9) - 1;
+		shift = 12;
+		break;
+	default:
+		pr_err("encode_insn_immediate: unknown immediate encoding %d\n",
+			type);
+		return 0;
+	}
+
+	/* Update the immediate field. */
+	insn &= ~(mask << shift);
+	insn |= (imm & mask) << shift;
+
+	return insn;
+}
+
+static int reloc_insn_movw(enum aarch64_reloc_op op, void *place, u64 val,
+			   int lsb, enum aarch64_imm_type imm_type)
+{
+	u64 imm, limit = 0;
+	s64 sval;
+	u32 insn = *(u32 *)place;
+
+	sval = do_reloc(op, place, val);
+	sval >>= lsb;
+	imm = sval & 0xffff;
+
+	/* Update the instruction with the new encoding. */
+	*(u32 *)place = encode_insn_immediate(imm_type, insn, imm);
+
+	/* Shift out the immediate field. */
+	sval >>= 16;
+
+	/*
+	 * For unsigned immediates, the overflow check is straightforward.
+	 * For signed immediates, the sign bit is actually the bit past the
+	 * most significant bit of the field.
+	 * The INSN_IMM_16 immediate type is unsigned.
+	 */
+	if (imm_type != INSN_IMM_16) {
+		sval++;
+		limit++;
+	}
+
+	/* Check the upper bits depending on the sign of the immediate. */
+	if ((u64)sval > limit)
+		return -ERANGE;
+
+	return 0;
+}
+
+static int reloc_insn_imm(enum aarch64_reloc_op op, void *place, u64 val,
+			  int lsb, int len, enum aarch64_imm_type imm_type)
+{
+	u64 imm, imm_mask;
+	s64 sval;
+	u32 insn = *(u32 *)place;
+
+	/* Calculate the relocation value. */
+	sval = do_reloc(op, place, val);
+	sval >>= lsb;
+
+	/* Extract the value bits and shift them to bit 0. */
+	imm_mask = (BIT(lsb + len) - 1) >> lsb;
+	imm = sval & imm_mask;
+
+	/* Update the instruction's immediate field. */
+	*(u32 *)place = encode_insn_immediate(imm_type, insn, imm);
+
+	/*
+	 * Extract the upper value bits (including the sign bit) and
+	 * shift them to bit 0.
+	 */
+	sval = (s64)(sval & ~(imm_mask >> 1)) >> (len - 1);
+
+	/*
+	 * Overflow has occurred if the upper bits are not all equal to
+	 * the sign bit of the value.
+	 */
+	if ((u64)(sval + 1) >= 2)
+		return -ERANGE;
+
+	return 0;
+}
+
+int apply_relocate_add(Elf64_Shdr *sechdrs,
+		       const char *strtab,
+		       unsigned int symindex,
+		       unsigned int relsec,
+		       struct module *me)
+{
+	unsigned int i;
+	int ovf;
+	bool overflow_check;
+	Elf64_Sym *sym;
+	void *loc;
+	u64 val;
+	Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
+
+	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
+		/* loc corresponds to P in the AArch64 ELF document. */
+		loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+			+ rel[i].r_offset;
+
+		/* sym is the ELF symbol we're referring to. */
+		sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
+			+ ELF64_R_SYM(rel[i].r_info);
+
+		/* val corresponds to (S + A) in the AArch64 ELF document. */
+		val = sym->st_value + rel[i].r_addend;
+
+		/* Check for overflow by default. */
+		overflow_check = true;
+
+		/* Perform the static relocation. */
+		switch (ELF64_R_TYPE(rel[i].r_info)) {
+		/* Null relocations. */
+		case R_ARM_NONE:
+		case R_AARCH64_NONE:
+			ovf = 0;
+			break;
+
+		/* Data relocations. */
+		case R_AARCH64_ABS64:
+			overflow_check = false;
+			ovf = reloc_data(RELOC_OP_ABS, loc, val, 64);
+			break;
+		case R_AARCH64_ABS32:
+			ovf = reloc_data(RELOC_OP_ABS, loc, val, 32);
+			break;
+		case R_AARCH64_ABS16:
+			ovf = reloc_data(RELOC_OP_ABS, loc, val, 16);
+			break;
+		case R_AARCH64_PREL64:
+			overflow_check = false;
+			ovf = reloc_data(RELOC_OP_PREL, loc, val, 64);
+			break;
+		case R_AARCH64_PREL32:
+			ovf = reloc_data(RELOC_OP_PREL, loc, val, 32);
+			break;
+		case R_AARCH64_PREL16:
+			ovf = reloc_data(RELOC_OP_PREL, loc, val, 16);
+			break;
+
+		/* MOVW instruction relocations. */
+		case R_AARCH64_MOVW_UABS_G0_NC:
+			overflow_check = false;
+		case R_AARCH64_MOVW_UABS_G0:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 0,
+					      INSN_IMM_16);
+			break;
+		case R_AARCH64_MOVW_UABS_G1_NC:
+			overflow_check = false;
+		case R_AARCH64_MOVW_UABS_G1:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 16,
+					      INSN_IMM_16);
+			break;
+		case R_AARCH64_MOVW_UABS_G2_NC:
+			overflow_check = false;
+		case R_AARCH64_MOVW_UABS_G2:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 32,
+					      INSN_IMM_16);
+			break;
+		case R_AARCH64_MOVW_UABS_G3:
+			/* We're using the top bits so we can't overflow. */
+			overflow_check = false;
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 48,
+					      INSN_IMM_16);
+			break;
+		case R_AARCH64_MOVW_SABS_G0:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 0,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_SABS_G1:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 16,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_SABS_G2:
+			ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 32,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_PREL_G0_NC:
+			overflow_check = false;
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 0,
+					      INSN_IMM_MOVK);
+			break;
+		case R_AARCH64_MOVW_PREL_G0:
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 0,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_PREL_G1_NC:
+			overflow_check = false;
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 16,
+					      INSN_IMM_MOVK);
+			break;
+		case R_AARCH64_MOVW_PREL_G1:
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 16,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_PREL_G2_NC:
+			overflow_check = false;
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 32,
+					      INSN_IMM_MOVK);
+			break;
+		case R_AARCH64_MOVW_PREL_G2:
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 32,
+					      INSN_IMM_MOVNZ);
+			break;
+		case R_AARCH64_MOVW_PREL_G3:
+			/* We're using the top bits so we can't overflow. */
+			overflow_check = false;
+			ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 48,
+					      INSN_IMM_MOVNZ);
+			break;
+
+		/* Immediate instruction relocations. */
+		case R_AARCH64_LD_PREL_LO19:
+			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 19,
+					     INSN_IMM_19);
+			break;
+		case R_AARCH64_ADR_PREL_LO21:
+			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 0, 21,
+					     INSN_IMM_ADR);
+			break;
+		case R_AARCH64_ADR_PREL_PG_HI21_NC:
+			overflow_check = false;
+		case R_AARCH64_ADR_PREL_PG_HI21:
+			ovf = reloc_insn_imm(RELOC_OP_PAGE, loc, val, 12, 21,
+					     INSN_IMM_ADR);
+			break;
+		case R_AARCH64_ADD_ABS_LO12_NC:
+		case R_AARCH64_LDST8_ABS_LO12_NC:
+			overflow_check = false;
+			ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 0, 12,
+					     INSN_IMM_12);
+			break;
+		case R_AARCH64_LDST16_ABS_LO12_NC:
+			overflow_check = false;
+			ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 1, 11,
+					     INSN_IMM_12);
+			break;
+		case R_AARCH64_LDST32_ABS_LO12_NC:
+			overflow_check = false;
+			ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 2, 10,
+					     INSN_IMM_12);
+			break;
+		case R_AARCH64_LDST64_ABS_LO12_NC:
+			overflow_check = false;
+			ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 3, 9,
+					     INSN_IMM_12);
+			break;
+		case R_AARCH64_LDST128_ABS_LO12_NC:
+			overflow_check = false;
+			ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 4, 8,
+					     INSN_IMM_12);
+			break;
+		case R_AARCH64_TSTBR14:
+			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 14,
+					     INSN_IMM_14);
+			break;
+		case R_AARCH64_CONDBR19:
+			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 19,
+					     INSN_IMM_19);
+			break;
+		case R_AARCH64_JUMP26:
+		case R_AARCH64_CALL26:
+			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
+					     INSN_IMM_26);
+			break;
+
+		default:
+			pr_err("module %s: unsupported RELA relocation: %llu\n",
+			       me->name, ELF64_R_TYPE(rel[i].r_info));
+			return -ENOEXEC;
+		}
+
+		if (overflow_check && ovf == -ERANGE)
+			goto overflow;
+
+	}
+
+	return 0;
+
+overflow:
+	pr_err("module %s: overflow in relocation type %d val %Lx\n",
+	       me->name, (int)ELF64_R_TYPE(rel[i].r_info), val);
+	return -ENOEXEC;
+}