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baa41469a7
linux/tools/objtool/arch/x86/decode.c
Josh Poimboeuf baa41469a7 objtool: Implement stack validation 2.0 
This is a major rewrite of objtool.  Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-30 10:19:19 +02:00

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/*
* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* 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/>.
*/
#include <stdio.h>
#include <stdlib.h>
#define unlikely(cond) (cond)
#include "insn/insn.h"
#include "insn/inat.c"
#include "insn/insn.c"
#include "../../elf.h"
#include "../../arch.h"
#include "../../warn.h"
static unsigned char op_to_cfi_reg[][2] = {
{CFI_AX, CFI_R8},
{CFI_CX, CFI_R9},
{CFI_DX, CFI_R10},
{CFI_BX, CFI_R11},
{CFI_SP, CFI_R12},
{CFI_BP, CFI_R13},
{CFI_SI, CFI_R14},
{CFI_DI, CFI_R15},
};
static int is_x86_64(struct elf *elf)
{
switch (elf->ehdr.e_machine) {
case EM_X86_64:
return 1;
case EM_386:
return 0;
default:
WARN("unexpected ELF machine type %d", elf->ehdr.e_machine);
return -1;
}
}
bool arch_callee_saved_reg(unsigned char reg)
{
switch (reg) {
case CFI_BP:
case CFI_BX:
case CFI_R12:
case CFI_R13:
case CFI_R14:
case CFI_R15:
return true;
case CFI_AX:
case CFI_CX:
case CFI_DX:
case CFI_SI:
case CFI_DI:
case CFI_SP:
case CFI_R8:
case CFI_R9:
case CFI_R10:
case CFI_R11:
case CFI_RA:
default:
return false;
}
}
int arch_decode_instruction(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int maxlen,
unsigned int *len, unsigned char *type,
unsigned long *immediate, struct stack_op *op)
{
struct insn insn;
int x86_64, sign;
unsigned char op1, op2, rex = 0, rex_b = 0, rex_r = 0, rex_w = 0,
modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
sib = 0;
x86_64 = is_x86_64(elf);
if (x86_64 == -1)
return -1;
insn_init(&insn, sec->data->d_buf + offset, maxlen, x86_64);
insn_get_length(&insn);
if (!insn_complete(&insn)) {
WARN_FUNC("can't decode instruction", sec, offset);
return -1;
}
*len = insn.length;
*type = INSN_OTHER;
if (insn.vex_prefix.nbytes)
return 0;
op1 = insn.opcode.bytes[0];
op2 = insn.opcode.bytes[1];
if (insn.rex_prefix.nbytes) {
rex = insn.rex_prefix.bytes[0];
rex_w = X86_REX_W(rex) >> 3;
rex_r = X86_REX_R(rex) >> 2;
rex_b = X86_REX_B(rex);
}
if (insn.modrm.nbytes) {
modrm = insn.modrm.bytes[0];
modrm_mod = X86_MODRM_MOD(modrm);
modrm_reg = X86_MODRM_REG(modrm);
modrm_rm = X86_MODRM_RM(modrm);
}
if (insn.sib.nbytes)
sib = insn.sib.bytes[0];
switch (op1) {
case 0x1:
case 0x29:
if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
/* add/sub reg, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_SRC_REG;
op->dest.reg = CFI_SP;
}
break;
case 0x50 ... 0x57:
/* push reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
op->dest.type = OP_DEST_PUSH;
break;
case 0x58 ... 0x5f:
/* pop reg */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
break;
case 0x68:
case 0x6a:
/* push immediate */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
break;
case 0x70 ... 0x7f:
*type = INSN_JUMP_CONDITIONAL;
break;
case 0x81:
case 0x83:
if (rex != 0x48)
break;
if (modrm == 0xe4) {
/* and imm, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_AND;
op->src.reg = CFI_SP;
op->src.offset = insn.immediate.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (modrm == 0xc4)
sign = 1;
else if (modrm == 0xec)
sign = -1;
else
break;
/* add/sub imm, %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = insn.immediate.value * sign;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
case 0x89:
if (rex == 0x48 && modrm == 0xe5) {
/* mov %rsp, %rbp */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = CFI_SP;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_BP;
break;
}
/* fallthrough */
case 0x88:
if (!rex_b &&
(modrm_mod == 1 || modrm_mod == 2) && modrm_rm == 5) {
/* mov reg, disp(%rbp) */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_BP;
op->dest.offset = insn.displacement.value;
} else if (rex_w && !rex_b && modrm_rm == 4 && sib == 0x24) {
/* mov reg, disp(%rsp) */
*type = INSN_STACK;
op->src.type = OP_SRC_REG;
op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
op->dest.type = OP_DEST_REG_INDIRECT;
op->dest.reg = CFI_SP;
op->dest.offset = insn.displacement.value;
}
break;
case 0x8b:
if (rex_w && !rex_b && modrm_mod == 1 && modrm_rm == 5) {
/* mov disp(%rbp), reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG_INDIRECT;
op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
} else if (rex_w && !rex_b && sib == 0x24 &&
modrm_mod != 3 && modrm_rm == 4) {
/* mov disp(%rsp), reg */
*type = INSN_STACK;
op->src.type = OP_SRC_REG_INDIRECT;
op->src.reg = CFI_SP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
}
break;
case 0x8d:
if (rex == 0x48 && modrm == 0x65) {
/* lea -disp(%rbp), %rsp */
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_BP;
op->src.offset = insn.displacement.value;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (rex == 0x4c && modrm == 0x54 && sib == 0x24 &&
insn.displacement.value == 8) {
/*
* lea 0x8(%rsp), %r10
*
* Here r10 is the "drap" pointer, used as a stack
* pointer helper when the stack gets realigned.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = 8;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_R10;
break;
}
if (rex == 0x4c && modrm == 0x6c && sib == 0x24 &&
insn.displacement.value == 16) {
/*
* lea 0x10(%rsp), %r13
*
* Here r13 is the "drap" pointer, used as a stack
* pointer helper when the stack gets realigned.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_SP;
op->src.offset = 16;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_R13;
break;
}
if (rex == 0x49 && modrm == 0x62 &&
insn.displacement.value == -8) {
/*
* lea -0x8(%r10), %rsp
*
* Restoring rsp back to its original value after a
* stack realignment.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_R10;
op->src.offset = -8;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
if (rex == 0x49 && modrm == 0x65 &&
insn.displacement.value == -16) {
/*
* lea -0x10(%r13), %rsp
*
* Restoring rsp back to its original value after a
* stack realignment.
*/
*type = INSN_STACK;
op->src.type = OP_SRC_ADD;
op->src.reg = CFI_R13;
op->src.offset = -16;
op->dest.type = OP_DEST_REG;
op->dest.reg = CFI_SP;
break;
}
break;
case 0x8f:
/* pop to mem */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
break;
case 0x90:
*type = INSN_NOP;
break;
case 0x9c:
/* pushf */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
break;
case 0x9d:
/* popf */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
break;
case 0x0f:
if (op2 >= 0x80 && op2 <= 0x8f)
*type = INSN_JUMP_CONDITIONAL;
else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
op2 == 0x35)
/* sysenter, sysret */
*type = INSN_CONTEXT_SWITCH;
else if (op2 == 0x0d || op2 == 0x1f)
/* nopl/nopw */
*type = INSN_NOP;
else if (op2 == 0xa0 || op2 == 0xa8) {
/* push fs/gs */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
} else if (op2 == 0xa1 || op2 == 0xa9) {
/* pop fs/gs */
*type = INSN_STACK;
op->src.type = OP_SRC_POP;
op->dest.type = OP_DEST_MEM;
}
break;
case 0xc9:
/*
* leave
*
* equivalent to:
* mov bp, sp
* pop bp
*/
*type = INSN_STACK;
op->dest.type = OP_DEST_LEAVE;
break;
case 0xe3:
/* jecxz/jrcxz */
*type = INSN_JUMP_CONDITIONAL;
break;
case 0xe9:
case 0xeb:
*type = INSN_JUMP_UNCONDITIONAL;
break;
case 0xc2:
case 0xc3:
*type = INSN_RETURN;
break;
case 0xca: /* retf */
case 0xcb: /* retf */
case 0xcf: /* iret */
*type = INSN_CONTEXT_SWITCH;
break;
case 0xe8:
*type = INSN_CALL;
break;
case 0xff:
if (modrm_reg == 2 || modrm_reg == 3)
*type = INSN_CALL_DYNAMIC;
else if (modrm_reg == 4)
*type = INSN_JUMP_DYNAMIC;
else if (modrm_reg == 5)
/* jmpf */
*type = INSN_CONTEXT_SWITCH;
else if (modrm_reg == 6) {
/* push from mem */
*type = INSN_STACK;
op->src.type = OP_SRC_CONST;
op->dest.type = OP_DEST_PUSH;
}
break;
default:
break;
}
*immediate = insn.immediate.nbytes ? insn.immediate.value : 0;
return 0;
}
void arch_initial_func_cfi_state(struct cfi_state *state)
{
int i;
for (i = 0; i < CFI_NUM_REGS; i++) {
state->regs[i].base = CFI_UNDEFINED;
state->regs[i].offset = 0;
}
/* initial CFA (call frame address) */
state->cfa.base = CFI_SP;
state->cfa.offset = 8;
/* initial RA (return address) */
state->regs[16].base = CFI_CFA;
state->regs[16].offset = -8;
}
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