问题
This is essentially what I'm trying to do,
#include <sys/mman.h>
int zero() {
return 0;
}
int main(int argc, const char *argv[]) {
return mprotect((void *) &zero, 4096, PROT_READ | PROT_WRITE);
}
so I'm trying to make code writable, essentially. This doesn't work on the current macOS (Catalina 10.15.2), it just returns -1
and sets errno
to EACCES
, which as far as I know is because of lack of entitlement/code signing. I've found the entitlement I need to set, but I have no idea how to go about that, nor how to actually sign it..
If I run codesign -d --entitlements :- <path_to_app>
, it fails with code object is not signed at all
, even though I've tried configuring signing in Xcode for a while (I have a certificate and so on). So how should I go about this? Actually signing it isn't obvious with Xcode, so I'm fairly clueless.
回答1:
This is not a definitive answer, but it's a workaround.
Your problem is caused by changes of the linker (ld64) in macOS Catalina. The default value of the max_prot
attribute of the __TEXT
segment in the Mach-O header has been changed.
Previously max_prot
default value was 0x7
(PROT_READ | PROT_WRITE | PROT_EXEC
).
The default value has now been changed to 0x5
(PROT_READ | PROT_EXEC
).
This means that mprotect
cannot make any region that resides within __TEXT
writable.
In theory, this should be resolved by providing the linker flag -segprot __TEXT rwx rx
, but this is not the case. Since Catalina, the max_prot
field is ignored. Instead, max_prot
is set to the value of init_prot
(see here).
To top it all off, init_prot
cannot be set to rwx
either due to macOS refusing to execute a file which has a writable __TEXT(init_prot)
attribute.
A brute workaround is to manually modify and set __TEXT(max_prot)
to 0x7
after linking.
printf '\x07' | dd of=<executable> bs=1 seek=160 count=1 conv=notrunc
Since that code snippet relies on the __TEXT(max_prot)
offset being hardcoded to 0xA0
, as an alternative, I've created a drop-in replacement/wrapper for ld
which respects the max_prot
parameter of segprot
.
来源:https://stackoverflow.com/questions/60654834/using-mprotect-to-make-text-segment-writable-on-macos