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Diffstat (limited to 'arch/x86/lib/insn-eval.c')
| -rw-r--r-- | arch/x86/lib/insn-eval.c | 1364 |
1 files changed, 1364 insertions, 0 deletions
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c new file mode 100644 index 000000000000..9119d8e41f1f --- /dev/null +++ b/arch/x86/lib/insn-eval.c @@ -0,0 +1,1364 @@ +/* + * Utility functions for x86 operand and address decoding + * + * Copyright (C) Intel Corporation 2017 + */ +#include <linux/kernel.h> +#include <linux/string.h> +#include <linux/ratelimit.h> +#include <linux/mmu_context.h> +#include <asm/desc_defs.h> +#include <asm/desc.h> +#include <asm/inat.h> +#include <asm/insn.h> +#include <asm/insn-eval.h> +#include <asm/ldt.h> +#include <asm/vm86.h> + +#undef pr_fmt +#define pr_fmt(fmt) "insn: " fmt + +enum reg_type { + REG_TYPE_RM = 0, + REG_TYPE_INDEX, + REG_TYPE_BASE, +}; + +/** + * is_string_insn() - Determine if instruction is a string instruction + * @insn: Instruction containing the opcode to inspect + * + * Returns: + * + * true if the instruction, determined by the opcode, is any of the + * string instructions as defined in the Intel Software Development manual. + * False otherwise. + */ +static bool is_string_insn(struct insn *insn) +{ + insn_get_opcode(insn); + + /* All string instructions have a 1-byte opcode. */ + if (insn->opcode.nbytes != 1) + return false; + + switch (insn->opcode.bytes[0]) { + case 0x6c ... 0x6f: /* INS, OUTS */ + case 0xa4 ... 0xa7: /* MOVS, CMPS */ + case 0xaa ... 0xaf: /* STOS, LODS, SCAS */ + return true; + default: + return false; + } +} + +/** + * get_seg_reg_override_idx() - obtain segment register override index + * @insn: Valid instruction with segment override prefixes + * + * Inspect the instruction prefixes in @insn and find segment overrides, if any. + * + * Returns: + * + * A constant identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_DEFAULT is returned if no segment override + * prefixes were found. + * + * -EINVAL in case of error. + */ +static int get_seg_reg_override_idx(struct insn *insn) +{ + int idx = INAT_SEG_REG_DEFAULT; + int num_overrides = 0, i; + + insn_get_prefixes(insn); + + /* Look for any segment override prefixes. */ + for (i = 0; i < insn->prefixes.nbytes; i++) { + insn_attr_t attr; + + attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); + switch (attr) { + case INAT_MAKE_PREFIX(INAT_PFX_CS): + idx = INAT_SEG_REG_CS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_SS): + idx = INAT_SEG_REG_SS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_DS): + idx = INAT_SEG_REG_DS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_ES): + idx = INAT_SEG_REG_ES; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_FS): + idx = INAT_SEG_REG_FS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_GS): + idx = INAT_SEG_REG_GS; + num_overrides++; + break; + /* No default action needed. */ + } + } + + /* More than one segment override prefix leads to undefined behavior. */ + if (num_overrides > 1) + return -EINVAL; + + return idx; +} + +/** + * check_seg_overrides() - check if segment override prefixes are allowed + * @insn: Valid instruction with segment override prefixes + * @regoff: Operand offset, in pt_regs, for which the check is performed + * + * For a particular register used in register-indirect addressing, determine if + * segment override prefixes can be used. Specifically, no overrides are allowed + * for rDI if used with a string instruction. + * + * Returns: + * + * True if segment override prefixes can be used with the register indicated + * in @regoff. False if otherwise. + */ +static bool check_seg_overrides(struct insn *insn, int regoff) +{ + if (regoff == offsetof(struct pt_regs, di) && is_string_insn(insn)) + return false; + + return true; +} + +/** + * resolve_default_seg() - resolve default segment register index for an operand + * @insn: Instruction with opcode and address size. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @off: Operand offset, in pt_regs, for which resolution is needed + * + * Resolve the default segment register index associated with the instruction + * operand register indicated by @off. Such index is resolved based on defaults + * described in the Intel Software Development Manual. + * + * Returns: + * + * If in protected mode, a constant identifying the segment register to use, + * among CS, SS, ES or DS. If in long mode, INAT_SEG_REG_IGNORE. + * + * -EINVAL in case of error. + */ +static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off) +{ + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + /* + * Resolve the default segment register as described in Section 3.7.4 + * of the Intel Software Development Manual Vol. 1: + * + * + DS for all references involving r[ABCD]X, and rSI. + * + If used in a string instruction, ES for rDI. Otherwise, DS. + * + AX, CX and DX are not valid register operands in 16-bit address + * encodings but are valid for 32-bit and 64-bit encodings. + * + -EDOM is reserved to identify for cases in which no register + * is used (i.e., displacement-only addressing). Use DS. + * + SS for rSP or rBP. + * + CS for rIP. + */ + + switch (off) { + case offsetof(struct pt_regs, ax): + case offsetof(struct pt_regs, cx): + case offsetof(struct pt_regs, dx): + /* Need insn to verify address size. */ + if (insn->addr_bytes == 2) + return -EINVAL; + + case -EDOM: + case offsetof(struct pt_regs, bx): + case offsetof(struct pt_regs, si): + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, di): + if (is_string_insn(insn)) + return INAT_SEG_REG_ES; + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, bp): + case offsetof(struct pt_regs, sp): + return INAT_SEG_REG_SS; + + case offsetof(struct pt_regs, ip): + return INAT_SEG_REG_CS; + + default: + return -EINVAL; + } +} + +/** + * resolve_seg_reg() - obtain segment register index + * @insn: Instruction with operands + * @regs: Register values as seen when entering kernel mode + * @regoff: Operand offset, in pt_regs, used to deterimine segment register + * + * Determine the segment register associated with the operands and, if + * applicable, prefixes and the instruction pointed by @insn. + * + * The segment register associated to an operand used in register-indirect + * addressing depends on: + * + * a) Whether running in long mode (in such a case segments are ignored, except + * if FS or GS are used). + * + * b) Whether segment override prefixes can be used. Certain instructions and + * registers do not allow override prefixes. + * + * c) Whether segment overrides prefixes are found in the instruction prefixes. + * + * d) If there are not segment override prefixes or they cannot be used, the + * default segment register associated with the operand register is used. + * + * The function checks first if segment override prefixes can be used with the + * operand indicated by @regoff. If allowed, obtain such overridden segment + * register index. Lastly, if not prefixes were found or cannot be used, resolve + * the segment register index to use based on the defaults described in the + * Intel documentation. In long mode, all segment register indexes will be + * ignored, except if overrides were found for FS or GS. All these operations + * are done using helper functions. + * + * The operand register, @regoff, is represented as the offset from the base of + * pt_regs. + * + * As stated, the main use of this function is to determine the segment register + * index based on the instruction, its operands and prefixes. Hence, @insn + * must be valid. However, if @regoff indicates rIP, we don't need to inspect + * @insn at all as in this case CS is used in all cases. This case is checked + * before proceeding further. + * + * Please note that this function does not return the value in the segment + * register (i.e., the segment selector) but our defined index. The segment + * selector needs to be obtained using get_segment_selector() and passing the + * segment register index resolved by this function. + * + * Returns: + * + * An index identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_IGNORE is returned if running in long mode. + * + * -EINVAL in case of error. + */ +static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) +{ + int idx; + + /* + * In the unlikely event of having to resolve the segment register + * index for rIP, do it first. Segment override prefixes should not + * be used. Hence, it is not necessary to inspect the instruction, + * which may be invalid at this point. + */ + if (regoff == offsetof(struct pt_regs, ip)) { + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + else + return INAT_SEG_REG_CS; + } + + if (!insn) + return -EINVAL; + + if (!check_seg_overrides(insn, regoff)) + return resolve_default_seg(insn, regs, regoff); + + idx = get_seg_reg_override_idx(insn); + if (idx < 0) + return idx; + + if (idx == INAT_SEG_REG_DEFAULT) + return resolve_default_seg(insn, regs, regoff); + + /* + * In long mode, segment override prefixes are ignored, except for + * overrides for FS and GS. + */ + if (user_64bit_mode(regs)) { + if (idx != INAT_SEG_REG_FS && + idx != INAT_SEG_REG_GS) + idx = INAT_SEG_REG_IGNORE; + } + + return idx; +} + +/** + * get_segment_selector() - obtain segment selector + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Segment register index to use + * + * Obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment + * registers. In CONFIG_X86_32, the segment is obtained from either pt_regs or + * kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained + * from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU + * registers. This done for only for completeness as in CONFIG_X86_64 segment + * registers are ignored. + * + * Returns: + * + * Value of the segment selector, including null when running in + * long mode. + * + * -EINVAL on error. + */ +static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) +{ +#ifdef CONFIG_X86_64 + unsigned short sel; + + switch (seg_reg_idx) { + case INAT_SEG_REG_IGNORE: + return 0; + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + savesegment(ds, sel); + return sel; + case INAT_SEG_REG_ES: + savesegment(es, sel); + return sel; + case INAT_SEG_REG_FS: + savesegment(fs, sel); + return sel; + case INAT_SEG_REG_GS: + savesegment(gs, sel); + return sel; + default: + return -EINVAL; + } +#else /* CONFIG_X86_32 */ + struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs; + + if (v8086_mode(regs)) { + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return vm86regs->ds; + case INAT_SEG_REG_ES: + return vm86regs->es; + case INAT_SEG_REG_FS: + return vm86regs->fs; + case INAT_SEG_REG_GS: + return vm86regs->gs; + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } + } + + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return (unsigned short)(regs->ds & 0xffff); + case INAT_SEG_REG_ES: + return (unsigned short)(regs->es & 0xffff); + case INAT_SEG_REG_FS: + return (unsigned short)(regs->fs & 0xffff); + case INAT_SEG_REG_GS: + /* + * GS may or may not be in regs as per CONFIG_X86_32_LAZY_GS. + * The macro below takes care of both cases. + */ + return get_user_gs(regs); + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } +#endif /* CONFIG_X86_64 */ +} + +static int get_reg_offset(struct insn *insn, struct pt_regs *regs, + enum reg_type type) +{ + int regno = 0; + + static const int regoff[] = { + offsetof(struct pt_regs, ax), + offsetof(struct pt_regs, cx), + offsetof(struct pt_regs, dx), + offsetof(struct pt_regs, bx), + offsetof(struct pt_regs, sp), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), +#ifdef CONFIG_X86_64 + offsetof(struct pt_regs, r8), + offsetof(struct pt_regs, r9), + offsetof(struct pt_regs, r10), + offsetof(struct pt_regs, r11), + offsetof(struct pt_regs, r12), + offsetof(struct pt_regs, r13), + offsetof(struct pt_regs, r14), + offsetof(struct pt_regs, r15), +#endif + }; + int nr_registers = ARRAY_SIZE(regoff); + /* + * Don't possibly decode a 32-bit instructions as + * reading a 64-bit-only register. + */ + if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64) + nr_registers -= 8; + + switch (type) { + case REG_TYPE_RM: + regno = X86_MODRM_RM(insn->modrm.value); + + /* + * ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement + * follows the ModRM byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; + + if (X86_REX_B(insn->rex_prefix.value)) + regno += 8; + break; + + case REG_TYPE_INDEX: + regno = X86_SIB_INDEX(insn->sib.value); + if (X86_REX_X(insn->rex_prefix.value)) + regno += 8; + + /* + * If ModRM.mod != 3 and SIB.index = 4 the scale*index + * portion of the address computation is null. This is + * true only if REX.X is 0. In such a case, the SIB index + * is used in the address computation. + */ + if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4) + return -EDOM; + break; + + case REG_TYPE_BASE: + regno = X86_SIB_BASE(insn->sib.value); + /* + * If ModRM.mod is 0 and SIB.base == 5, the base of the + * register-indirect addressing is 0. In this case, a + * 32-bit displacement follows the SIB byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; + + if (X86_REX_B(insn->rex_prefix.value)) + regno += 8; + break; + + default: + pr_err_ratelimited("invalid register type: %d\n", type); + return -EINVAL; + } + + if (regno >= nr_registers) { + WARN_ONCE(1, "decoded an instruction with an invalid register"); + return -EINVAL; + } + return regoff[regno]; +} + +/** + * get_reg_offset_16() - Obtain offset of register indicated by instruction + * @insn: Instruction containing ModRM byte + * @regs: Register values as seen when entering kernel mode + * @offs1: Offset of the first operand register + * @offs2: Offset of the second opeand register, if applicable + * + * Obtain the offset, in pt_regs, of the registers indicated by the ModRM byte + * in @insn. This function is to be used with 16-bit address encodings. The + * @offs1 and @offs2 will be written with the offset of the two registers + * indicated by the instruction. In cases where any of the registers is not + * referenced by the instruction, the value will be set to -EDOM. + * + * Returns: + * + * 0 on success, -EINVAL on error. + */ +static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs, + int *offs1, int *offs2) +{ + /* + * 16-bit addressing can use one or two registers. Specifics of + * encodings are given in Table 2-1. "16-Bit Addressing Forms with the + * ModR/M Byte" of the Intel Software Development Manual. + */ + static const int regoff1[] = { + offsetof(struct pt_regs, bx), + offsetof(struct pt_regs, bx), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, bx), + }; + + static const int regoff2[] = { + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), + -EDOM, + -EDOM, + -EDOM, + -EDOM, + }; + + if (!offs1 || !offs2) + return -EINVAL; + + /* Operand is a register, use the generic function. */ + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + *offs1 = insn_get_modrm_rm_off(insn, regs); + *offs2 = -EDOM; + return 0; + } + + *offs1 = regoff1[X86_MODRM_RM(insn->modrm.value)]; + *offs2 = regoff2[X86_MODRM_RM(insn->modrm.value)]; + + /* + * If ModRM.mod is 0 and ModRM.rm is 110b, then we use displacement- + * only addressing. This means that no registers are involved in + * computing the effective address. Thus, ensure that the first + * register offset is invalild. The second register offset is already + * invalid under the aforementioned conditions. + */ + if ((X86_MODRM_MOD(insn->modrm.value) == 0) && + (X86_MODRM_RM(insn->modrm.value) == 6)) + *offs1 = -EDOM; + + return 0; +} + +/** + * get_desc() - Obtain pointer to a segment descriptor + * @sel: Segment selector + * + * Given a segment selector, obtain a pointer to the segment descriptor. + * Both global and local descriptor tables are supported. + * + * Returns: + * + * Pointer to segment descriptor on success. + * + * NULL on error. + */ +static struct desc_struct *get_desc(unsigned short sel) +{ + struct desc_ptr gdt_desc = {0, 0}; + unsigned long desc_base; + +#ifdef CONFIG_MODIFY_LDT_SYSCALL + if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) { + struct desc_struct *desc = NULL; + struct ldt_struct *ldt; + + /* Bits [15:3] contain the index of the desired entry. */ + sel >>= 3; + + mutex_lock(¤t->active_mm->context.lock); + ldt = current->active_mm->context.ldt; + if (ldt && sel < ldt->nr_entries) + desc = &ldt->entries[sel]; + + mutex_unlock(¤t->active_mm->context.lock); + + return desc; + } +#endif + native_store_gdt(&gdt_desc); + + /* + * Segment descriptors have a size of 8 bytes. Thus, the index is + * multiplied by 8 to obtain the memory offset of the desired descriptor + * from the base of the GDT. As bits [15:3] of the segment selector + * contain the index, it can be regarded as multiplied by 8 already. + * All that remains is to clear bits [2:0]. + */ + desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); + + if (desc_base > gdt_desc.size) + return NULL; + + return (struct desc_struct *)(gdt_desc.address + desc_base); +} + +/** + * insn_get_seg_base() - Obtain base address of segment descriptor. + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Index of the segment register pointing to seg descriptor + * + * Obtain the base address of the segment as indicated by the segment descriptor + * pointed by the segment selector. The segment selector is obtained from the + * input segment register index @seg_reg_idx. + * + * Returns: + * + * In protected mode, base address of the segment. Zero in long mode, + * except when FS or GS are used. In virtual-8086 mode, the segment + * selector shifted 4 bits to the right. + * + * -1L in case of error. + */ +unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx) +{ + struct desc_struct *desc; + short sel; + + sel = get_segment_selector(regs, seg_reg_idx); + if (sel < 0) + return -1L; + + if (v8086_mode(regs)) + /* + * Base is simply the segment selector shifted 4 + * bits to the right. + */ + return (unsigned long)(sel << 4); + + if (user_64bit_mode(regs)) { + /* + * Only FS or GS will have a base address, the rest of + * the segments' bases are forced to 0. + */ + unsigned long base; + + if (seg_reg_idx == INAT_SEG_REG_FS) + rdmsrl(MSR_FS_BASE, base); + else if (seg_reg_idx == INAT_SEG_REG_GS) + /* + * swapgs was called at the kernel entry point. Thus, + * MSR_KERNEL_GS_BASE will have the user-space GS base. + */ + rdmsrl(MSR_KERNEL_GS_BASE, base); + else + base = 0; + return base; + } + + /* In protected mode the segment selector cannot be null. */ + if (!sel) + return -1L; + + desc = get_desc(sel); + if (!desc) + return -1L; + + return get_desc_base(desc); +} + +/** + * get_seg_limit() - Obtain the limit of a segment descriptor + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Index of the segment register pointing to seg descriptor + * + * Obtain the limit of the segment as indicated by the segment descriptor + * pointed by the segment selector. The segment selector is obtained from the + * input segment register index @seg_reg_idx. + * + * Returns: + * + * In protected mode, the limit of the segment descriptor in bytes. + * In long mode and virtual-8086 mode, segment limits are not enforced. Thus, + * limit is returned as -1L to imply a limit-less segment. + * + * Zero is returned on error. + */ +static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx) +{ + struct desc_struct *desc; + unsigned long limit; + short sel; + + sel = get_segment_selector(regs, seg_reg_idx); + if (sel < 0) + return 0; + + if (user_64bit_mode(regs) || v8086_mode(regs)) + return -1L; + + if (!sel) + return 0; + + desc = get_desc(sel); + if (!desc) + return 0; + + /* + * If the granularity bit is set, the limit is given in multiples + * of 4096. This also means that the 12 least significant bits are + * not tested when checking the segment limits. In practice, + * this means that the segment ends in (limit << 12) + 0xfff. + */ + limit = get_desc_limit(desc); + if (desc->g) + limit = (limit << 12) + 0xfff; + + return limit; +} + +/** + * insn_get_code_seg_params() - Obtain code segment parameters + * @regs: Structure with register values as seen when entering kernel mode + * + * Obtain address and operand sizes of the code segment. It is obtained from the + * selector contained in the CS register in regs. In protected mode, the default + * address is determined by inspecting the L and D bits of the segment + * descriptor. In virtual-8086 mode, the default is always two bytes for both + * address and operand sizes. + * + * Returns: + * + * An int containing ORed-in default parameters on success. + * + * -EINVAL on error. + */ +int insn_get_code_seg_params(struct pt_regs *regs) +{ + struct desc_struct *desc; + short sel; + + if (v8086_mode(regs)) + /* Address and operand size are both 16-bit. */ + return INSN_CODE_SEG_PARAMS(2, 2); + + sel = get_segment_selector(regs, INAT_SEG_REG_CS); + if (sel < 0) + return sel; + + desc = get_desc(sel); + if (!desc) + return -EINVAL; + + /* + * The most significant byte of the Type field of the segment descriptor + * determines whether a segment contains data or code. If this is a data + * segment, return error. + */ + if (!(desc->type & BIT(3))) + return -EINVAL; + + switch ((desc->l << 1) | desc->d) { + case 0: /* + * Legacy mode. CS.L=0, CS.D=0. Address and operand size are + * both 16-bit. + */ + return INSN_CODE_SEG_PARAMS(2, 2); + case 1: /* + * Legacy mode. CS.L=0, CS.D=1. Address and operand size are + * both 32-bit. + */ + return INSN_CODE_SEG_PARAMS(4, 4); + case 2: /* + * IA-32e 64-bit mode. CS.L=1, CS.D=0. Address size is 64-bit; + * operand size is 32-bit. + */ + return INSN_CODE_SEG_PARAMS(4, 8); + case 3: /* Invalid setting. CS.L=1, CS.D=1 */ + /* fall through */ + default: + return -EINVAL; + } +} + +/** + * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte + * @insn: Instruction containing the ModRM byte + * @regs: Register values as seen when entering kernel mode + * + * Returns: + * + * The register indicated by the r/m part of the ModRM byte. The + * register is obtained as an offset from the base of pt_regs. In specific + * cases, the returned value can be -EDOM to indicate that the particular value + * of ModRM does not refer to a register and shall be ignored. + */ +int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) +{ + return get_reg_offset(insn, regs, REG_TYPE_RM); +} + +/** + * get_seg_base_limit() - obtain base address and limit of a segment + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Operand offset, in pt_regs, used to resolve segment descriptor + * @base: Obtained segment base + * @limit: Obtained segment limit + * + * Obtain the base address and limit of the segment associated with the operand + * @regoff and, if any or allowed, override prefixes in @insn. This function is + * different from insn_get_seg_base() as the latter does not resolve the segment + * associated with the instruction operand. If a limit is not needed (e.g., + * when running in long mode), @limit can be NULL. + * + * Returns: + * + * 0 on success. @base and @limit will contain the base address and of the + * resolved segment, respectively. + * + * -EINVAL on error. + */ +static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs, + int regoff, unsigned long *base, + unsigned long *limit) +{ + int seg_reg_idx; + + if (!base) + return -EINVAL; + + seg_reg_idx = resolve_seg_reg(insn, regs, regoff); + if (seg_reg_idx < 0) + return seg_reg_idx; + + *base = insn_get_seg_base(regs, seg_reg_idx); + if (*base == -1L) + return -EINVAL; + + if (!limit) + return 0; + + *limit = get_seg_limit(regs, seg_reg_idx); + if (!(*limit)) + return -EINVAL; + + return 0; +} + +/** + * get_eff_addr_reg() - Obtain effective address from register operand + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Obtained operand offset, in pt_regs, with the effective address + * @eff_addr: Obtained effective address + * + * Obtain the effective address stored in the register operand as indicated by + * the ModRM byte. This function is to be used only with register addressing + * (i.e., ModRM.mod is 3). The effective address is saved in @eff_addr. The + * register operand, as an offset from the base of pt_regs, is saved in @regoff; + * such offset can then be used to resolve the segment associated with the + * operand. This function can be used with any of the supported address sizes + * in x86. + * + * Returns: + * + * 0 on success. @eff_addr will have the effective address stored in the + * operand indicated by ModRM. @regoff will have such operand as an offset from + * the base of pt_regs. + * + * -EINVAL on error. + */ +static int get_eff_addr_reg(struct insn *insn, struct pt_regs *regs, + int *regoff, long *eff_addr) +{ + insn_get_modrm(insn); + + if (!insn->modrm.nbytes) + return -EINVAL; + + if (X86_MODRM_MOD(insn->modrm.value) != 3) + return -EINVAL; + + *regoff = get_reg_offset(insn, regs, REG_TYPE_RM); + if (*regoff < 0) + return -EINVAL; + + /* Ignore bytes that are outside the address size. */ + if (insn->addr_bytes == 2) + *eff_addr = regs_get_register(regs, *regoff) & 0xffff; + else if (insn->addr_bytes == 4) + *eff_addr = regs_get_register(regs, *regoff) & 0xffffffff; + else /* 64-bit address */ + *eff_addr = regs_get_register(regs, *regoff); + + return 0; +} + +/** + * get_eff_addr_modrm() - Obtain referenced effective address via ModRM + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Obtained operand offset, in pt_regs, associated with segment + * @eff_addr: Obtained effective address + * + * Obtain the effective address referenced by the ModRM byte of @insn. After + * identifying the registers involved in the register-indirect memory reference, + * its value is obtained from the operands in @regs. The computed address is + * stored @eff_addr. Also, the register operand that indicates the associated + * segment is stored in @regoff, this parameter can later be used to determine + * such segment. + * + * Returns: + * + * 0 on success. @eff_addr will have the referenced effective address. @regoff + * will have a register, as an offset from the base of pt_regs, that can be used + * to resolve the associated segment. + * + * -EINVAL on error. + */ +static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs, + int *regoff, long *eff_addr) +{ + long tmp; + + if (insn->addr_bytes != 8 && insn->addr_bytes != 4) + return -EINVAL; + + insn_get_modrm(insn); + + if (!insn->modrm.nbytes) + return -EINVAL; + + if (X86_MODRM_MOD(insn->modrm.value) > 2) + return -EINVAL; + + *regoff = get_reg_offset(insn, regs, REG_TYPE_RM); + + /* + * -EDOM means that we must ignore the address_offset. In such a case, + * in 64-bit mode the effective address relative to the rIP of the + * following instruction. + */ + if (*regoff == -EDOM) { + if (user_64bit_mode(regs)) + tmp = regs->ip + insn->length; + else + tmp = 0; + } else if (*regoff < 0) { + return -EINVAL; + } else { + tmp = regs_get_register(regs, *regoff); + } + + if (insn->addr_bytes == 4) { + int addr32 = (int)(tmp & 0xffffffff) + insn->displacement.value; + + *eff_addr = addr32 & 0xffffffff; + } else { + *eff_addr = tmp + insn->displacement.value; + } + + return 0; +} + +/** + * get_eff_addr_modrm_16() - Obtain referenced effective address via ModRM + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Obtained operand offset, in pt_regs, associated with segment + * @eff_addr: Obtained effective address + * + * Obtain the 16-bit effective address referenced by the ModRM byte of @insn. + * After identifying the registers involved in the register-indirect memory + * reference, its value is obtained from the operands in @regs. The computed + * address is stored @eff_addr. Also, the register operand that indicates + * the associated segment is stored in @regoff, this parameter can later be used + * to determine such segment. + * + * Returns: + * + * 0 on success. @eff_addr will have the referenced effective address. @regoff + * will have a register, as an offset from the base of pt_regs, that can be used + * to resolve the associated segment. + * + * -EINVAL on error. + */ +static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs, + int *regoff, short *eff_addr) +{ + int addr_offset1, addr_offset2, ret; + short addr1 = 0, addr2 = 0, displacement; + + if (insn->addr_bytes != 2) + return -EINVAL; + + insn_get_modrm(insn); + + if (!insn->modrm.nbytes) + return -EINVAL; + + if (X86_MODRM_MOD(insn->modrm.value) > 2) + return -EINVAL; + + ret = get_reg_offset_16(insn, regs, &addr_offset1, &addr_offset2); + if (ret < 0) + return -EINVAL; + + /* + * Don't fail on invalid offset values. They might be invalid because + * they cannot be used for this particular value of ModRM. Instead, use + * them in the computation only if they contain a valid value. + */ + if (addr_offset1 != -EDOM) + addr1 = regs_get_register(regs, addr_offset1) & 0xffff; + + if (addr_offset2 != -EDOM) + addr2 = regs_get_register(regs, addr_offset2) & 0xffff; + + displacement = insn->displacement.value & 0xffff; + *eff_addr = addr1 + addr2 + displacement; + + /* + * The first operand register could indicate to use of either SS or DS + * registers to obtain the segment selector. The second operand + * register can only indicate the use of DS. Thus, the first operand + * will be used to obtain the segment selector. + */ + *regoff = addr_offset1; + + return 0; +} + +/** + * get_eff_addr_sib() - Obtain referenced effective address via SIB + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Obtained operand offset, in pt_regs, associated with segment + * @eff_addr: Obtained effective address + * + * Obtain the effective address referenced by the SIB byte of @insn. After + * identifying the registers involved in the indexed, register-indirect memory + * reference, its value is obtained from the operands in @regs. The computed + * address is stored @eff_addr. Also, the register operand that indicates the + * associated segment is stored in @regoff, this parameter can later be used to + * determine such segment. + * + * Returns: + * + * 0 on success. @eff_addr will have the referenced effective address. + * @base_offset will have a register, as an offset from the base of pt_regs, + * that can be used to resolve the associated segment. + * + * -EINVAL on error. + */ +static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs, + int *base_offset, long *eff_addr) +{ + long base, indx; + int indx_offset; + + if (insn->addr_bytes != 8 && insn->addr_bytes != 4) + return -EINVAL; + + insn_get_modrm(insn); + + if (!insn->modrm.nbytes) + return -EINVAL; + + if (X86_MODRM_MOD(insn->modrm.value) > 2) + return -EINVAL; + + insn_get_sib(insn); + + if (!insn->sib.nbytes) + return -EINVAL; + + *base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); + indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); + + /* + * Negative values in the base and index offset means an error when + * decoding the SIB byte. Except -EDOM, which means that the registers + * should not be used in the address computation. + */ + if (*base_offset == -EDOM) + base = 0; + else if (*base_offset < 0) + return -EINVAL; + else + base = regs_get_register(regs, *base_offset); + + if (indx_offset == -EDOM) + indx = 0; + else if (indx_offset < 0) + return -EINVAL; + else + indx = regs_get_register(regs, indx_offset); + + if (insn->addr_bytes == 4) { + int addr32, base32, idx32; + + base32 = base & 0xffffffff; + idx32 = indx & 0xffffffff; + + addr32 = base32 + idx32 * (1 << X86_SIB_SCALE(insn->sib.value)); + addr32 += insn->displacement.value; + + *eff_addr = addr32 & 0xffffffff; + } else { + *eff_addr = base + indx * (1 << X86_SIB_SCALE(insn->sib.value)); + *eff_addr += insn->displacement.value; + } + + return 0; +} + +/** + * get_addr_ref_16() - Obtain the 16-bit address referred by instruction + * @insn: Instruction containing ModRM byte and displacement + * @regs: Register values as seen when entering kernel mode + * + * This function is to be used with 16-bit address encodings. Obtain the memory + * address referred by the instruction's ModRM and displacement bytes. Also, the + * segment used as base is determined by either any segment override prefixes in + * @insn or the default segment of the registers involved in the address + * computation. In protected mode, segment limits are enforced. + * + * Returns: + * + * Linear address referenced by the instruction operands on success. + * + * -1L on error. + */ +static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs) +{ + unsigned long linear_addr = -1L, seg_base, seg_limit; + int ret, regoff; + short eff_addr; + long tmp; + + insn_get_modrm(insn); + insn_get_displacement(insn); + + if (insn->addr_bytes != 2) + goto out; + + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + ret = get_eff_addr_reg(insn, regs, ®off, &tmp); + if (ret) + goto out; + + eff_addr = tmp; + } else { + ret = get_eff_addr_modrm_16(insn, regs, ®off, &eff_addr); + if (ret) + goto out; + } + + ret = get_seg_base_limit(insn, regs, regoff, &seg_base, &seg_limit); + if (ret) + goto out; + + /* + * Before computing the linear address, make sure the effective address + * is within the limits of the segment. In virtual-8086 mode, segment + * limits are not enforced. In such a case, the segment limit is -1L to + * reflect this fact. + */ + if ((unsigned long)(eff_addr & 0xffff) > seg_limit) + goto out; + + linear_addr = (unsigned long)(eff_addr & 0xffff) + seg_base; + + /* Limit linear address to 20 bits */ + if (v8086_mode(regs)) + linear_addr &= 0xfffff; + +out: + return (void __user *)linear_addr; +} + +/** + * get_addr_ref_32() - Obtain a 32-bit linear address + * @insn: Instruction with ModRM, SIB bytes and displacement + * @regs: Register values as seen when entering kernel mode + * + * This function is to be used with 32-bit address encodings to obtain the + * linear memory address referred by the instruction's ModRM, SIB, + * displacement bytes and segment base address, as applicable. If in protected + * mode, segment limits are enforced. + * + * Returns: + * + * Linear address referenced by instruction and registers on success. + * + * -1L on error. + */ +static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs) +{ + unsigned long linear_addr = -1L, seg_base, seg_limit; + int eff_addr, regoff; + long tmp; + int ret; + + if (insn->addr_bytes != 4) + goto out; + + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + ret = get_eff_addr_reg(insn, regs, ®off, &tmp); + if (ret) + goto out; + + eff_addr = tmp; + + } else { + if (insn->sib.nbytes) { + ret = get_eff_addr_sib(insn, regs, ®off, &tmp); + if (ret) + goto out; + + eff_addr = tmp; + } else { + ret = get_eff_addr_modrm(insn, regs, ®off, &tmp); + if (ret) + goto out; + + eff_addr = tmp; + } + } + + ret = get_seg_base_limit(insn, regs, regoff, &seg_base, &seg_limit); + if (ret) + goto out; + + /* + * In protected mode, before computing the linear address, make sure + * the effective address is within the limits of the segment. + * 32-bit addresses can be used in long and virtual-8086 modes if an + * address override prefix is used. In such cases, segment limits are + * not enforced. When in virtual-8086 mode, the segment limit is -1L + * to reflect this situation. + * + * After computed, the effective address is treated as an unsigned + * quantity. + */ + if (!user_64bit_mode(regs) && ((unsigned int)eff_addr > seg_limit)) + goto out; + + /* + * Even though 32-bit address encodings are allowed in virtual-8086 + * mode, the address range is still limited to [0x-0xffff]. + */ + if (v8086_mode(regs) && (eff_addr & ~0xffff)) + goto out; + + /* + * Data type long could be 64 bits in size. Ensure that our 32-bit + * effective address is not sign-extended when computing the linear + * address. + */ + linear_addr = (unsigned long)(eff_addr & 0xffffffff) + seg_base; + + /* Limit linear address to 20 bits */ + if (v8086_mode(regs)) + linear_addr &= 0xfffff; + +out: + return (void __user *)linear_addr; +} + +/** + * get_addr_ref_64() - Obtain a 64-bit linear address + * @insn: Instruction struct with ModRM and SIB bytes and displacement + * @regs: Structure with register values as seen when entering kernel mode + * + * This function is to be used with 64-bit address encodings to obtain the + * linear memory address referred by the instruction's ModRM, SIB, + * displacement bytes and segment base address, as applicable. + * + * Returns: + * + * Linear address referenced by instruction and registers on success. + * + * -1L on error. + */ +#ifndef CONFIG_X86_64 +static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) +{ + return (void __user *)-1L; +} +#else +static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) +{ + unsigned long linear_addr = -1L, seg_base; + int regoff, ret; + long eff_addr; + + if (insn->addr_bytes != 8) + goto out; + + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + ret = get_eff_addr_reg(insn, regs, ®off, &eff_addr); + if (ret) + goto out; + + } else { + if (insn->sib.nbytes) { + ret = get_eff_addr_sib(insn, regs, ®off, &eff_addr); + if (ret) + goto out; + } else { + ret = get_eff_addr_modrm(insn, regs, ®off, &eff_addr); + if (ret) + goto out; + } + + } + + ret = get_seg_base_limit(insn, regs, regoff, &seg_base, NULL); + if (ret) + goto out; + + linear_addr = (unsigned long)eff_addr + seg_base; + +out: + return (void __user *)linear_addr; +} +#endif /* CONFIG_X86_64 */ + +/** + * insn_get_addr_ref() - Obtain the linear address referred by instruction + * @insn: Instruction structure containing ModRM byte and displacement + * @regs: Structure with register values as seen when entering kernel mode + * + * Obtain the linear address referred by the instruction's ModRM, SIB and + * displacement bytes, and segment base, as applicable. In protected mode, + * segment limits are enforced. + * + * Returns: + * + * Linear address referenced by instruction and registers on success. + * + * -1L on error. + */ +void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) +{ + if (!insn || !regs) + return (void __user *)-1L; + + switch (insn->addr_bytes) { + case 2: + return get_addr_ref_16(insn, regs); + case 4: + return get_addr_ref_32(insn, regs); + case 8: + return get_addr_ref_64(insn, regs); + default: + return (void __user *)-1L; + } +} |