MacOS Catalina上的ld64 segprot无法正常工作? [英] ld64 segprot on MacOS Catalina not working?

问题描述

我想在MacOS Catalina(64位)上创建一个二进制文件，并使其具有可执行的数据段(请参见

I want to create a binary on MacOS Catalina (64 bit) with a data segment that can be made executable (see here for details) but is not executable from the start.

我用

gcc -nostdlib -segprot __DATA rwx rw- .... 

我还用gcc创建了一个目标文件，然后直接调用ld. ld版本是

I also created an object file with gcc and then called ld directly. The ld version is

$ ld -v
@(#)PROGRAM:ld  PROJECT:ld64-530
BUILD 18:57:17 Dec 13 2019
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
LTO support using: LLVM version 11.0.0, (clang-1100.0.33.17) (static support for 23, runtime is 23)
TAPI support using: Apple TAPI version 11.0.0 (tapi-1100.0.11)

该应该使数据段最初为RW，但是让我使用mprotect将该段中的权限扩展为RWX.

That should make the data segment initially RW, but allow me to use mprotect to extend permission in that segment to RWX.

但是，我注意到__DATA段的初始权限和最大权限为RW:

However, I notice that the __DATA segment is RW for initial and max permission:

$ otool -l jonesforth
.
.
.
Load command 2
      cmd LC_SEGMENT_64
  cmdsize 312
  segname __DATA
   vmaddr 0x0000000100001000
   vmsize 0x0000000000024000
  fileoff 4096
 filesize 4096
  maxprot 0x00000003
 initprot 0x00000003
   nsects 3
    flags 0x0
Section
.
.
.

有什么我想念的吗? darwin文档此处说:

Is there something I'm missing? The darwin documentation here says:

-segprot name max init (32-bit only)

              Specifies the maximum and initial virtual memory  protection  of
              the  named segment, name, to be max and init ,respectively.  The
              values for max and init are any combination  of  the  characters
              `r'  (for  read), `w' (for write), `x' (for execute) and '-' (no
              access).  The default is `rwx' for the  maximum  protection  for
              all segments for PowerPC architecures and `rw` for the all Intel
              architecures.  The default for the initial  protection  for  all
              segments  is  `rw'  unless  the segment contains a section which
              contains some machine instructions, in which  case  the  default
              for  the initial protection is `rwx' (and for Intel architecures
              it also sets the maximum protection to `rwx' in this case).  The
              default for the initial protection for the ``__TEXT'' segment is
              `rx' (not writable).

当然，那是darwin(仅32位)文档，但这是我发现的唯一内容. 我怀疑gcc不正确地支持darwin保护语法，或者它已损坏，或者darwin中的内容从x86更改为x64.

Of course, that the darwin (32 bit only) documentation but it's the only thing I found. I suspect that either gcc does not 'properly' support the darwin protection syntax, or it's broken, or things in darwin changed from x86 to x64.

任何指针都会很棒，谢谢.

Any pointers would be great, thanks in advance.

推荐答案

是的，3月18日发生了一些事情:

Yes, something did happen on March 18:

Apple 进行了更改使得ld对于非i386架构(包括x64)(例如Catalina)始终设置maxprot = initprot.尚不清楚这是否是故意的，这与ld联机帮助页不符.

Apple committed a change that makes ld always set maxprot = initprot for non-i386 architectures, so including x64, ie Catalina. It's unclear whether this was intentional, it's at odds with the ld manpage.

一种解决方法当然是在initprot中为整个段设置所需的保护级别.如果想要更精细的控制，则可以将所需的数据/代码移动到单独的段中.

One workaround is of course to set the desired protection level for the entire segment in initprot. One can probably move the desired data/code into a separate segment if one wants to have finer grained control.

另一种解决方法，这要感谢 Darfink 的评论:还可以更改链接器或修改所需的maxprot ld运行后. Darfink指出了他的 ld64包装器，一个python脚本，以使其自动化.

Another workaround, thanks to the comment from Darfink: One can also change the linker or modify the desired maxprot after ld runs. Darfink pointed out his ld64 wrapper, a python script, to automate this.

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