macOS v10.15(Catalina)/x64上的自修改代码 [英] Self-modifying code on macOS v10.15 (Catalina) / x64
问题描述
作为移植Forth编译器的一部分，我试图创建一个允许自我修改代码的二进制文件.详细信息位于 https://github.com/klapauciusisgreat/jonesforth-MacOS-x64
As part as porting a Forth compiler, I'm trying to create a binary that allows for self-modifying code. The gory details are at https://github.com/klapauciusisgreat/jonesforth-MacOS-x64
理想情况下，我为用户定义创建了一堆页面，然后像这样调用mprotect:
Ideally, I create a bunch of pages for user definitions and call mprotect like so:
#define __NR_exit 0x2000001
#define __NR_open 0x2000005
#define __NR_close 0x2000006
#define __NR_read 0x2000003
#define __NR_write 0x2000004
#define __NR_mprotect 0x200004a
#define PROT_READ 0x01
#define PROT_WRITE 0x02
#define PROT_EXEC 0x04
#define PROT_ALL (PROT_READ | PROT_WRITE | PROT_EXEC)
#define PAGE_SIZE 4096
// https://opensource.apple.com/source/xnu/xnu-201/bsd/sys/errno.h
#define EACCES 13 /* Permission denied */
#define EINVAL 22 /* Invalid argument */
#define ENOTSUP 45 /* Operation not supported */
/* Assembler entry point. */
.text
.globl start
start:
// Use mprotect to allow read/write/execute of the .bss section
mov $__NR_mprotect, %rax // mprotect
lea user_defs_start(%rip), %rdi // Start address
and $-PAGE_SIZE,%rdi // Align at page boundary
mov $USER_DEFS_SIZE, %rsi // Length
mov $PROT_ALL,%rdx
syscall
cmp $EINVAL, %rax
je 1f
cmp $EACCES,%rax
je 2f
test %rax,%rax
je 4f // All good, proceed:
// must be ENOTSUP
mov $2,%rdi // First parameter: stderr
lea errENOTSUP(%rip),%rsi // Second parameter: error message
mov $8,%rdx // Third parameter: length of string
mov $__NR_write,%rax // Write syscall
syscall
jmp 3f
1:
mov $2,%rdi // First parameter: stderr
lea errEINVAL(%rip),%rsi // Second parameter: error message
mov $7,%rdx // Third parameter: length of string
mov $__NR_write,%rax // Write syscall
syscall
jmp 3f
2:
mov $2,%rdi // First parameter: stderr
lea errEACCES(%rip),%rsi // Second parameter: error message
mov $7,%rdx // Third parameter: length of string
mov $__NR_write,%rax // Write syscall
syscall
3:
// did't work -- then exit
xor %rdi,%rdi
mov $__NR_exit,%rax // syscall: exit
syscall
4:
// All good, let's get started for real:
.
.
.
.set RETURN_STACK_SIZE,8192
.set BUFFER_SIZE,4096
.set USER_DEFS_SIZE,65536*2 // 128 kiB ought to be enough for everybody
.bss
.balign 8
user_defs_start:
.space USER_DEFS_SIZE
但是，我得到了EACCES返回值.我怀疑这是因为苹果已经设置了一些安全策略，但是我找不到很好的文档.
However, I get an EACCES return value. I suspect that this is because of some security policy apple has set up, but I do not find good documentation.
mprotect的源代码在哪里，和/或将数据区域同时标记为可执行和可写的方法是什么?
Where is the source code for mprotect, and/or what are the methods to mark the data area executable and writable at the same time?
我发现可以使用
gcc -segprot __DATA rwx rwx
确实标记了整个数据段rwx，因此必须以某种方式可以做正确的事情.但是我更希望仅使包含Forth单词的区域可执行，而不是整个数据段.
does mark the entire data segment rwx, so it must somehow be possible to do the right thing. But I would prefer to only make the area hosting Forth words executable, not the entire data segment.
I found a similar discussion here, but without any solution.
推荐答案
我要在其中取消保护"执行权限的段实际上有两个描述其权限的值:
The segment that I want to 'unprotect' exec permission in has really two values describing its permissions:
-
初始保护设置，我想为__DATA设置为rw-
the initial protection settings, which for __DATA I want rw-
最大保护(最松散)设置，我想成为rwx.
the maximum protection (loosest) settings, which I want to be rwx.
所以首先我需要将maxprot字段设置为rwx.根据ld联机帮助页，应通过使用标志-segprot __DATA rwx rw调用 gcc 或 ld 来实现.但是，Apple最近对链接器进行的更改实际上忽略了maxprot值，并设置了maxprot = initprot.
So first I need to set the maxprot field to rwx. According to the ld manpage, this should be achieved by invoking gcc or ld with the flags -segprot __DATA rwx rw. However, a recent change made by Apple to the linker essentially ignores the maxprot value, and sets maxprot=initprot.
由于 Darfink ，您可以使用
Thanks to Darfink, you can use this script to tweak the maxprot bits after the fact. I thought additional code signing with special entitlements was required, but it's not, at least for the __DATA segment. The __TEXT segment may need code signing with the com.apple.security.cs.disable-executable-page-protection entitlement.
另请参见此处.
从更大的角度看，我还应该指出，与其取消保护原本受保护的__DATA段的片段，不如为具有rwx权限的自修改代码创建一个完整的新数据/代码段可能更好.开始.这样一来，仍然可以由操作系统保护其余数据，并且不需要非标准工具.
Looking at the larger picture, I should also point out that rather to unprotect pieces of an otherwise protected __DATA segment, it may be better to create a complete new data/code segment just for the self-modifying code with rwx permissions from the start. This allows still protecting the rest of data by the operating system, and requires no non-standard tools.
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