Commit 2071b3e3 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'x86/espfix' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next

Pull x86-64 espfix changes from Peter Anvin:
 "This is the espfix64 code, which fixes the IRET information leak as
  well as the associated functionality problem.  With this code applied,
  16-bit stack segments finally work as intended even on a 64-bit
  kernel.

  Consequently, this patchset also removes the runtime option that we
  added as an interim measure.

  To help the people working on Linux kernels for very small systems,
  this patchset also makes these compile-time configurable features"

* 'x86/espfix' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  Revert "x86-64, modify_ldt: Make support for 16-bit segments a runtime option"
  x86, espfix: Make it possible to disable 16-bit support
  x86, espfix: Make espfix64 a Kconfig option, fix UML
  x86, espfix: Fix broken header guard
  x86, espfix: Move espfix definitions into a separate header file
  x86-32, espfix: Remove filter for espfix32 due to race
  x86-64, espfix: Don't leak bits 31:16 of %esp returning to 16-bit stack
parents 9df0fe64 e6ab9a20
......@@ -12,6 +12,8 @@ ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
... unused hole ...
ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
... unused hole ...
ffffffff80000000 - ffffffffa0000000 (=512 MB) kernel text mapping, from phys 0
ffffffffa0000000 - ffffffffff5fffff (=1525 MB) module mapping space
ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
......
......@@ -912,10 +912,27 @@ config VM86
default y
depends on X86_32
---help---
This option is required by programs like DOSEMU to run 16-bit legacy
code on X86 processors. It also may be needed by software like
XFree86 to initialize some video cards via BIOS. Disabling this
option saves about 6k.
This option is required by programs like DOSEMU to run
16-bit real mode legacy code on x86 processors. It also may
be needed by software like XFree86 to initialize some video
cards via BIOS. Disabling this option saves about 6K.
config X86_16BIT
bool "Enable support for 16-bit segments" if EXPERT
default y
---help---
This option is required by programs like Wine to run 16-bit
protected mode legacy code on x86 processors. Disabling
this option saves about 300 bytes on i386, or around 6K text
plus 16K runtime memory on x86-64,
config X86_ESPFIX32
def_bool y
depends on X86_16BIT && X86_32
config X86_ESPFIX64
def_bool y
depends on X86_16BIT && X86_64
config TOSHIBA
tristate "Toshiba Laptop support"
......
#ifndef _ASM_X86_ESPFIX_H
#define _ASM_X86_ESPFIX_H
#ifdef CONFIG_X86_64
#include <asm/percpu.h>
DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
extern void init_espfix_bsp(void);
extern void init_espfix_ap(void);
#endif /* CONFIG_X86_64 */
#endif /* _ASM_X86_ESPFIX_H */
......@@ -61,6 +61,8 @@ typedef struct { pteval_t pte; } pte_t;
#define MODULES_VADDR (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
#define MODULES_END _AC(0xffffffffff000000, UL)
#define MODULES_LEN (MODULES_END - MODULES_VADDR)
#define ESPFIX_PGD_ENTRY _AC(-2, UL)
#define ESPFIX_BASE_ADDR (ESPFIX_PGD_ENTRY << PGDIR_SHIFT)
#define EARLY_DYNAMIC_PAGE_TABLES 64
......
......@@ -59,6 +59,8 @@ static inline void x86_ce4100_early_setup(void) { }
#ifndef _SETUP
#include <asm/espfix.h>
/*
* This is set up by the setup-routine at boot-time
*/
......
......@@ -29,6 +29,7 @@ obj-$(CONFIG_X86_64) += sys_x86_64.o x8664_ksyms_64.o
obj-y += syscall_$(BITS).o vsyscall_gtod.o
obj-$(CONFIG_X86_64) += vsyscall_64.o
obj-$(CONFIG_X86_64) += vsyscall_emu_64.o
obj-$(CONFIG_X86_ESPFIX64) += espfix_64.o
obj-$(CONFIG_SYSFS) += ksysfs.o
obj-y += bootflag.o e820.o
obj-y += pci-dma.o quirks.o topology.o kdebugfs.o
......
......@@ -527,6 +527,7 @@ syscall_exit:
restore_all:
TRACE_IRQS_IRET
restore_all_notrace:
#ifdef CONFIG_X86_ESPFIX32
movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS
# Warning: PT_OLDSS(%esp) contains the wrong/random values if we
# are returning to the kernel.
......@@ -537,6 +538,7 @@ restore_all_notrace:
cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax
CFI_REMEMBER_STATE
je ldt_ss # returning to user-space with LDT SS
#endif
restore_nocheck:
RESTORE_REGS 4 # skip orig_eax/error_code
irq_return:
......@@ -549,13 +551,9 @@ ENTRY(iret_exc)
.previous
_ASM_EXTABLE(irq_return,iret_exc)
#ifdef CONFIG_X86_ESPFIX32
CFI_RESTORE_STATE
ldt_ss:
larl PT_OLDSS(%esp), %eax
jnz restore_nocheck
testl $0x00400000, %eax # returning to 32bit stack?
jnz restore_nocheck # allright, normal return
#ifdef CONFIG_PARAVIRT
/*
* The kernel can't run on a non-flat stack if paravirt mode
......@@ -597,6 +595,7 @@ ldt_ss:
lss (%esp), %esp /* switch to espfix segment */
CFI_ADJUST_CFA_OFFSET -8
jmp restore_nocheck
#endif
CFI_ENDPROC
ENDPROC(system_call)
......@@ -704,6 +703,7 @@ END(syscall_badsys)
* the high word of the segment base from the GDT and swiches to the
* normal stack and adjusts ESP with the matching offset.
*/
#ifdef CONFIG_X86_ESPFIX32
/* fixup the stack */
mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
......@@ -713,8 +713,10 @@ END(syscall_badsys)
pushl_cfi %eax
lss (%esp), %esp /* switch to the normal stack segment */
CFI_ADJUST_CFA_OFFSET -8
#endif
.endm
.macro UNWIND_ESPFIX_STACK
#ifdef CONFIG_X86_ESPFIX32
movl %ss, %eax
/* see if on espfix stack */
cmpw $__ESPFIX_SS, %ax
......@@ -725,6 +727,7 @@ END(syscall_badsys)
/* switch to normal stack */
FIXUP_ESPFIX_STACK
27:
#endif
.endm
/*
......@@ -1355,11 +1358,13 @@ END(debug)
ENTRY(nmi)
RING0_INT_FRAME
ASM_CLAC
#ifdef CONFIG_X86_ESPFIX32
pushl_cfi %eax
movl %ss, %eax
cmpw $__ESPFIX_SS, %ax
popl_cfi %eax
je nmi_espfix_stack
#endif
cmpl $ia32_sysenter_target,(%esp)
je nmi_stack_fixup
pushl_cfi %eax
......@@ -1399,6 +1404,7 @@ nmi_debug_stack_check:
FIX_STACK 24, nmi_stack_correct, 1
jmp nmi_stack_correct
#ifdef CONFIG_X86_ESPFIX32
nmi_espfix_stack:
/* We have a RING0_INT_FRAME here.
*
......@@ -1420,6 +1426,7 @@ nmi_espfix_stack:
lss 12+4(%esp), %esp # back to espfix stack
CFI_ADJUST_CFA_OFFSET -24
jmp irq_return
#endif
CFI_ENDPROC
END(nmi)
......
......@@ -58,6 +58,7 @@
#include <asm/asm.h>
#include <asm/context_tracking.h>
#include <asm/smap.h>
#include <asm/pgtable_types.h>
#include <linux/err.h>
/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this. */
......@@ -1040,8 +1041,18 @@ restore_args:
RESTORE_ARGS 1,8,1
irq_return:
/*
* Are we returning to a stack segment from the LDT? Note: in
* 64-bit mode SS:RSP on the exception stack is always valid.
*/
#ifdef CONFIG_X86_ESPFIX64
testb $4,(SS-RIP)(%rsp)
jnz irq_return_ldt
#endif
irq_return_iret:
INTERRUPT_RETURN
_ASM_EXTABLE(irq_return, bad_iret)
_ASM_EXTABLE(irq_return_iret, bad_iret)
#ifdef CONFIG_PARAVIRT
ENTRY(native_iret)
......@@ -1049,6 +1060,32 @@ ENTRY(native_iret)
_ASM_EXTABLE(native_iret, bad_iret)
#endif
#ifdef CONFIG_X86_ESPFIX64
irq_return_ldt:
pushq_cfi %rax
pushq_cfi %rdi
SWAPGS
movq PER_CPU_VAR(espfix_waddr),%rdi
movq %rax,(0*8)(%rdi) /* RAX */
movq (2*8)(%rsp),%rax /* RIP */
movq %rax,(1*8)(%rdi)
movq (3*8)(%rsp),%rax /* CS */
movq %rax,(2*8)(%rdi)
movq (4*8)(%rsp),%rax /* RFLAGS */
movq %rax,(3*8)(%rdi)
movq (6*8)(%rsp),%rax /* SS */
movq %rax,(5*8)(%rdi)
movq (5*8)(%rsp),%rax /* RSP */
movq %rax,(4*8)(%rdi)
andl $0xffff0000,%eax
popq_cfi %rdi
orq PER_CPU_VAR(espfix_stack),%rax
SWAPGS
movq %rax,%rsp
popq_cfi %rax
jmp irq_return_iret
#endif
.section .fixup,"ax"
bad_iret:
/*
......@@ -1110,9 +1147,45 @@ ENTRY(retint_kernel)
call preempt_schedule_irq
jmp exit_intr
#endif
CFI_ENDPROC
END(common_interrupt)
/*
* If IRET takes a fault on the espfix stack, then we
* end up promoting it to a doublefault. In that case,
* modify the stack to make it look like we just entered
* the #GP handler from user space, similar to bad_iret.
*/
#ifdef CONFIG_X86_ESPFIX64
ALIGN
__do_double_fault:
XCPT_FRAME 1 RDI+8
movq RSP(%rdi),%rax /* Trap on the espfix stack? */
sarq $PGDIR_SHIFT,%rax
cmpl $ESPFIX_PGD_ENTRY,%eax
jne do_double_fault /* No, just deliver the fault */
cmpl $__KERNEL_CS,CS(%rdi)
jne do_double_fault
movq RIP(%rdi),%rax
cmpq $irq_return_iret,%rax
#ifdef CONFIG_PARAVIRT
je 1f
cmpq $native_iret,%rax
#endif
jne do_double_fault /* This shouldn't happen... */
1:
movq PER_CPU_VAR(kernel_stack),%rax
subq $(6*8-KERNEL_STACK_OFFSET),%rax /* Reset to original stack */
movq %rax,RSP(%rdi)
movq $0,(%rax) /* Missing (lost) #GP error code */
movq $general_protection,RIP(%rdi)
retq
CFI_ENDPROC
END(__do_double_fault)
#else
# define __do_double_fault do_double_fault
#endif
/*
* End of kprobes section
*/
......@@ -1289,7 +1362,7 @@ idtentry overflow do_overflow has_error_code=0
idtentry bounds do_bounds has_error_code=0
idtentry invalid_op do_invalid_op has_error_code=0
idtentry device_not_available do_device_not_available has_error_code=0
idtentry double_fault do_double_fault has_error_code=1 paranoid=1
idtentry double_fault __do_double_fault has_error_code=1 paranoid=1
idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
idtentry invalid_TSS do_invalid_TSS has_error_code=1
idtentry segment_not_present do_segment_not_present has_error_code=1
......@@ -1576,7 +1649,7 @@ error_sti:
*/
error_kernelspace:
incl %ebx
leaq irq_return(%rip),%rcx
leaq irq_return_iret(%rip),%rcx
cmpq %rcx,RIP+8(%rsp)
je error_swapgs
movl %ecx,%eax /* zero extend */
......
/* ----------------------------------------------------------------------- *
*
* Copyright 2014 Intel Corporation; author: H. Peter Anvin
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope 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.
*
* ----------------------------------------------------------------------- */
/*
* The IRET instruction, when returning to a 16-bit segment, only
* restores the bottom 16 bits of the user space stack pointer. This
* causes some 16-bit software to break, but it also leaks kernel state
* to user space.
*
* This works around this by creating percpu "ministacks", each of which
* is mapped 2^16 times 64K apart. When we detect that the return SS is
* on the LDT, we copy the IRET frame to the ministack and use the
* relevant alias to return to userspace. The ministacks are mapped
* readonly, so if the IRET fault we promote #GP to #DF which is an IST
* vector and thus has its own stack; we then do the fixup in the #DF
* handler.
*
* This file sets up the ministacks and the related page tables. The
* actual ministack invocation is in entry_64.S.
*/
#include <linux/init.h>
#include <linux/init_task.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/gfp.h>
#include <linux/random.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/setup.h>
#include <asm/espfix.h>
/*
* Note: we only need 6*8 = 48 bytes for the espfix stack, but round
* it up to a cache line to avoid unnecessary sharing.
*/
#define ESPFIX_STACK_SIZE (8*8UL)
#define ESPFIX_STACKS_PER_PAGE (PAGE_SIZE/ESPFIX_STACK_SIZE)
/* There is address space for how many espfix pages? */
#define ESPFIX_PAGE_SPACE (1UL << (PGDIR_SHIFT-PAGE_SHIFT-16))
#define ESPFIX_MAX_CPUS (ESPFIX_STACKS_PER_PAGE * ESPFIX_PAGE_SPACE)
#if CONFIG_NR_CPUS > ESPFIX_MAX_CPUS
# error "Need more than one PGD for the ESPFIX hack"
#endif
#define PGALLOC_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO)
/* This contains the *bottom* address of the espfix stack */
DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
/* Initialization mutex - should this be a spinlock? */
static DEFINE_MUTEX(espfix_init_mutex);
/* Page allocation bitmap - each page serves ESPFIX_STACKS_PER_PAGE CPUs */
#define ESPFIX_MAX_PAGES DIV_ROUND_UP(CONFIG_NR_CPUS, ESPFIX_STACKS_PER_PAGE)
static void *espfix_pages[ESPFIX_MAX_PAGES];
static __page_aligned_bss pud_t espfix_pud_page[PTRS_PER_PUD]
__aligned(PAGE_SIZE);
static unsigned int page_random, slot_random;
/*
* This returns the bottom address of the espfix stack for a specific CPU.
* The math allows for a non-power-of-two ESPFIX_STACK_SIZE, in which case
* we have to account for some amount of padding at the end of each page.
*/
static inline unsigned long espfix_base_addr(unsigned int cpu)
{
unsigned long page, slot;
unsigned long addr;
page = (cpu / ESPFIX_STACKS_PER_PAGE) ^ page_random;
slot = (cpu + slot_random) % ESPFIX_STACKS_PER_PAGE;
addr = (page << PAGE_SHIFT) + (slot * ESPFIX_STACK_SIZE);
addr = (addr & 0xffffUL) | ((addr & ~0xffffUL) << 16);
addr += ESPFIX_BASE_ADDR;
return addr;
}
#define PTE_STRIDE (65536/PAGE_SIZE)
#define ESPFIX_PTE_CLONES (PTRS_PER_PTE/PTE_STRIDE)
#define ESPFIX_PMD_CLONES PTRS_PER_PMD
#define ESPFIX_PUD_CLONES (65536/(ESPFIX_PTE_CLONES*ESPFIX_PMD_CLONES))
#define PGTABLE_PROT ((_KERNPG_TABLE & ~_PAGE_RW) | _PAGE_NX)
static void init_espfix_random(void)
{
unsigned long rand;
/*
* This is run before the entropy pools are initialized,
* but this is hopefully better than nothing.
*/
if (!arch_get_random_long(&rand)) {
/* The constant is an arbitrary large prime */
rdtscll(rand);
rand *= 0xc345c6b72fd16123UL;
}
slot_random = rand % ESPFIX_STACKS_PER_PAGE;
page_random = (rand / ESPFIX_STACKS_PER_PAGE)
& (ESPFIX_PAGE_SPACE - 1);
}
void __init init_espfix_bsp(void)
{
pgd_t *pgd_p;
pteval_t ptemask;
ptemask = __supported_pte_mask;
/* Install the espfix pud into the kernel page directory */
pgd_p = &init_level4_pgt[pgd_index(ESPFIX_BASE_ADDR)];
pgd_populate(&init_mm, pgd_p, (pud_t *)espfix_pud_page);
/* Randomize the locations */
init_espfix_random();
/* The rest is the same as for any other processor */
init_espfix_ap();
}
void init_espfix_ap(void)
{
unsigned int cpu, page;
unsigned long addr;
pud_t pud, *pud_p;
pmd_t pmd, *pmd_p;
pte_t pte, *pte_p;
int n;
void *stack_page;
pteval_t ptemask;
/* We only have to do this once... */
if (likely(this_cpu_read(espfix_stack)))
return; /* Already initialized */
cpu = smp_processor_id();
addr = espfix_base_addr(cpu);
page = cpu/ESPFIX_STACKS_PER_PAGE;
/* Did another CPU already set this up? */
stack_page = ACCESS_ONCE(espfix_pages[page]);
if (likely(stack_page))
goto done;
mutex_lock(&espfix_init_mutex);
/* Did we race on the lock? */
stack_page = ACCESS_ONCE(espfix_pages[page]);
if (stack_page)
goto unlock_done;
ptemask = __supported_pte_mask;
pud_p = &espfix_pud_page[pud_index(addr)];
pud = *pud_p;
if (!pud_present(pud)) {
pmd_p = (pmd_t *)__get_free_page(PGALLOC_GFP);
pud = __pud(__pa(pmd_p) | (PGTABLE_PROT & ptemask));
paravirt_alloc_pud(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
for (n = 0; n < ESPFIX_PUD_CLONES; n++)
set_pud(&pud_p[n], pud);
}
pmd_p = pmd_offset(&pud, addr);
pmd = *pmd_p;
if (!pmd_present(pmd)) {
pte_p = (pte_t *)__get_free_page(PGALLOC_GFP);
pmd = __pmd(__pa(pte_p) | (PGTABLE_PROT & ptemask));
paravirt_alloc_pmd(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
for (n = 0; n < ESPFIX_PMD_CLONES; n++)
set_pmd(&pmd_p[n], pmd);
}
pte_p = pte_offset_kernel(&pmd, addr);
stack_page = (void *)__get_free_page(GFP_KERNEL);
pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
paravirt_alloc_pte(&init_mm, __pa(stack_page) >> PAGE_SHIFT);
for (n = 0; n < ESPFIX_PTE_CLONES; n++)
set_pte(&pte_p[n*PTE_STRIDE], pte);
/* Job is done for this CPU and any CPU which shares this page */
ACCESS_ONCE(espfix_pages[page]) = stack_page;
unlock_done:
mutex_unlock(&espfix_init_mutex);
done:
this_cpu_write(espfix_stack, addr);
this_cpu_write(espfix_waddr, (unsigned long)stack_page
+ (addr & ~PAGE_MASK));
}
......@@ -20,8 +20,6 @@
#include <asm/mmu_context.h>
#include <asm/syscalls.h>
int sysctl_ldt16 = 0;
#ifdef CONFIG_SMP
static void flush_ldt(void *current_mm)
{
......@@ -231,16 +229,10 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
}
}
/*
* On x86-64 we do not support 16-bit segments due to
* IRET leaking the high bits of the kernel stack address.
*/
#ifdef CONFIG_X86_64
if (!ldt_info.seg_32bit && !sysctl_ldt16) {
if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
error = -EINVAL;
goto out_unlock;
}
#endif
fill_ldt(&ldt, &ldt_info);
if (oldmode)
......
......@@ -243,6 +243,13 @@ static void notrace start_secondary(void *unused)
*/
check_tsc_sync_target();
/*
* Enable the espfix hack for this CPU
*/
#ifdef CONFIG_X86_ESPFIX64
init_espfix_ap();
#endif
/*
* We need to hold vector_lock so there the set of online cpus
* does not change while we are assigning vectors to cpus. Holding
......
......@@ -30,12 +30,14 @@ struct pg_state {
unsigned long start_address;
unsigned long current_address;
const struct addr_marker *marker;
unsigned long lines;
bool to_dmesg;
};
struct addr_marker {
unsigned long start_address;
const char *name;
unsigned long max_lines;
};
/* indices for address_markers; keep sync'd w/ address_markers below */
......@@ -46,6 +48,7 @@ enum address_markers_idx {
LOW_KERNEL_NR,
VMALLOC_START_NR,
VMEMMAP_START_NR,
ESPFIX_START_NR,
HIGH_KERNEL_NR,
MODULES_VADDR_NR,
MODULES_END_NR,
......@@ -68,6 +71,7 @@ static struct addr_marker address_markers[] = {
{ PAGE_OFFSET, "Low Kernel Mapping" },
{ VMALLOC_START, "vmalloc() Area" },
{ VMEMMAP_START, "Vmemmap" },
{ ESPFIX_BASE_ADDR, "ESPfix Area", 16 },
{ __START_KERNEL_map, "High Kernel Mapping" },
{ MODULES_VADDR, "Modules" },
{ MODULES_END, "End Modules" },
......@@ -182,7 +186,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
pgprot_t new_prot, int level)
{
pgprotval_t prot, cur;
static const char units[] = "KMGTPE";
static const char units[] = "BKMGTPE";
/*
* If we have a "break" in the series, we need to flush the state that
......@@ -197,6 +201,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
st->current_prot = new_prot;
st->level = level;
st->marker = address_markers;
st->lines = 0;
pt_dump_seq_printf(m, st->to_dmesg, "---[ %s ]---\n",
st->marker->name);
} else if (prot != cur || level != st->level ||
......@@ -208,17 +213,24 @@ static void note_page(struct seq_file *m, struct pg_state *st,
/*
* Now print the actual finished series
*/
pt_dump_seq_printf(m, st->to_dmesg, "0x%0*lx-0x%0*lx ",
width, st->start_address,
width, st->current_address);
delta = (st->current_address - st->start_address) >> 10;
while (!(delta & 1023) && unit[1]) {
delta >>= 10;
unit++;
if (!st->marker->max_lines ||
st->lines < st->marker->max_lines) {
pt_dump_seq_printf(m, st->to_dmesg,
"0x%0*lx-0x%0*lx ",
width, st->start_address,
width, st->current_address);
delta = st->current_address - st->start_address;
while (!(delta & 1023) && unit[1]) {
delta >>= 10;