/*
* Figure out which fixups arch_uprobe_post_xol() will need to perform, and
* annotate arch_uprobe->fixups accordingly. To start with,
* arch_uprobe->fixups is either zero or it reflects rip-related fixups.
*/
static void prepare_fixups(struct arch_uprobe *auprobe, struct insn *insn)
{
bool fix_ip = true, fix_call = false; /* defaults */
int reg;
insn_get_opcode(insn); /* should be a nop */
switch (OPCODE1(insn)) {
case 0x9d:
/* popf */
auprobe->fixups |= UPROBE_FIX_SETF;
break;
case 0xc3: /* ret/lret */
case 0xcb:
case 0xc2:
case 0xca:
/* ip is correct */
fix_ip = false;
break;
case 0xe8: /* call relative - Fix return addr */
fix_call = true;
break;
case 0x9a: /* call absolute - Fix return addr, not ip */
fix_call = true;
fix_ip = false;
break;
case 0xff:
insn_get_modrm(insn);
reg = MODRM_REG(insn);
if (reg == 2 || reg == 3) {
/* call or lcall, indirect */
/* Fix return addr; ip is correct. */
fix_call = true;
fix_ip = false;
} else if (reg == 4 || reg == 5) {
/* jmp or ljmp, indirect */
/* ip is correct. */
fix_ip = false;
}
break;
case 0xea: /* jmp absolute -- ip is correct */
fix_ip = false;
break;
default:
break;
}
if (fix_ip)
auprobe->fixups |= UPROBE_FIX_IP;
if (fix_call)
auprobe->fixups |= UPROBE_FIX_CALL;
}
/**
* insn_rip_relative() - Does instruction use RIP-relative addressing mode?
* @insn: &struct insn containing instruction
*
* If necessary, first collects the instruction up to and including the
* ModRM byte. No effect if @insn->x86_64 is 0.
*/
int insn_rip_relative(struct insn *insn)
{
struct insn_field *modrm = &insn->modrm;
if (!insn->x86_64)
return 0;
if (!modrm->got)
insn_get_modrm(insn);
/*
* For rip-relative instructions, the mod field (top 2 bits)
* is zero and the r/m field (bottom 3 bits) is 0x5.
*/
return (modrm->nbytes && (modrm->value & 0xc7) == 0x5);
}
/**
* insn_get_sib() - Get the SIB byte of instruction
* @insn: &struct insn containing instruction
*
* If necessary, first collects the instruction up to and including the
* ModRM byte.
*/
void insn_get_sib(struct insn *insn)
{
insn_byte_t modrm;
if (insn->sib.got)
return;
if (!insn->modrm.got)
insn_get_modrm(insn);
if (insn->modrm.nbytes) {
modrm = (insn_byte_t)insn->modrm.value;
if (insn->addr_bytes != 2 &&
X86_MODRM_MOD(modrm) != 3 && X86_MODRM_RM(modrm) == 4) {
insn->sib.value = get_next(insn_byte_t, insn);
insn->sib.nbytes = 1;
}
}
insn->sib.got = 1;
}
/*
* return the address being referenced be instruction
* for rm=3 returning the content of the rm reg
* for rm!=3 calculates the address using SIB and Disp
*/
static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
unsigned long addr, base, indx;
int addr_offset, base_offset, indx_offset;
insn_byte_t sib;
insn_get_modrm(insn);
insn_get_sib(insn);
sib = insn->sib.value;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out_err;
addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
if (base_offset < 0)
goto out_err;
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
if (indx_offset < 0)
goto out_err;
base = regs_get_register(regs, base_offset);
indx = regs_get_register(regs, indx_offset);
addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out_err;
addr = regs_get_register(regs, addr_offset);
}
addr += insn->displacement.value;
}
return (void __user *)addr;
out_err:
return (void __user *)-1;
}
/*
* If a bounds overflow occurs then a #BR is generated. This
* function decodes MPX instructions to get violation address
* and set this address into extended struct siginfo.
*
* Note that this is not a super precise way of doing this.
* Userspace could have, by the time we get here, written
* anything it wants in to the instructions. We can not
* trust anything about it. They might not be valid
* instructions or might encode invalid registers, etc...
*
* The caller is expected to kfree() the returned siginfo_t.
*/
siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
{
const struct bndreg *bndregs, *bndreg;
siginfo_t *info = NULL;
struct insn insn;
uint8_t bndregno;
int err;
err = mpx_insn_decode(&insn, regs);
if (err)
goto err_out;
/*
* We know at this point that we are only dealing with
* MPX instructions.
*/
insn_get_modrm(&insn);
bndregno = X86_MODRM_REG(insn.modrm.value);
if (bndregno > 3) {
err = -EINVAL;
goto err_out;
}
/* get bndregs field from current task's xsave area */
bndregs = get_xsave_field_ptr(XSTATE_BNDREGS);
if (!bndregs) {
err = -EINVAL;
goto err_out;
}
/* now go select the individual register in the set of 4 */
bndreg = &bndregs[bndregno];
info = kzalloc(sizeof(*info), GFP_KERNEL);
if (!info) {
err = -ENOMEM;
goto err_out;
}
/*
* The registers are always 64-bit, but the upper 32
* bits are ignored in 32-bit mode. Also, note that the
* upper bounds are architecturally represented in 1's
* complement form.
*
* The 'unsigned long' cast is because the compiler
* complains when casting from integers to different-size
* pointers.
*/
info->si_lower = (void __user *)(unsigned long)bndreg->lower_bound;
info->si_upper = (void __user *)(unsigned long)~bndreg->upper_bound;
info->si_addr_lsb = 0;
info->si_signo = SIGSEGV;
info->si_errno = 0;
info->si_code = SEGV_BNDERR;
info->si_addr = mpx_get_addr_ref(&insn, regs);
/*
* We were not able to extract an address from the instruction,
* probably because there was something invalid in it.
*/
if (info->si_addr == (void *)-1) {
err = -EINVAL;
goto err_out;
}
trace_mpx_bounds_register_exception(info->si_addr, bndreg);
return info;
err_out:
/* info might be NULL, but kfree() handles that */
kfree(info);
return ERR_PTR(err);
}