Shiva is an ELF dynamic linker that is specialized for patching native Linux software. Shiva has been custom tailored towards the requirements of the DARPA AMP project and currently supports the AArch64 architecture.
Patches are written in C and compiled into ELF relocatable objects. Shiva loads, links, and patches the new code into memory.
OS: Linux Architectures: AArch64 ELF binary support: AArch64 ELF PIE executables (aka. ET_DYN)
Support for ET_EXEC binaries and other architectures are on the way.
This has been tested on aarch64 ubuntu 18.04 and ubuntu 22. Shiva relies on libelfmaster, musl-libc, and libcapstone.
git clone git@github.com:elfmaster/libelfmaster
cd libelfmaster
git --fetch all
git checkout aarch64_support
The original build for libelfmaster is broken and I haven't yet fixed it. Meanwhile just use the simple build shellscript I made.
cd src
sudo make.sh
The static library to libelfmaster
/opt/elfmaster/lib/libelfmaster.a
The header file to libelfmaster
/opt/elfmaster/include/elfmaster.h
sudo apt-get install musl musl-dev musl-tools
cd ~/git
git clone git@github.com:advanced-microcode-patching/shiva
cd shiva
make
make shiva-ld
make patches
sudo make install
Shiva is copied to "/lib/shiva" and can be executed directly or indirectly as
an interpreter.
The shiva-ld utility is known as the "Shiva Prelinker" and is used to modify
binaries with the path to the new program interpreter "/lib/shiva", and the
path to the patch module (i.e. "/opt/modules/shiva/patch1.o").
$ cd modules/aarch64/cfs_patch1
We have already compiled and prelinked the example patches in the previous steps. Shiva prelinking refers specifically to the prelinking applied by the shiva-ld tool.
Take a look at the Makefile for each patch, and you will see how shiva-ld is used to apply the pre-patch meta-data.
shiva-ld -e core-cpu1 -p cfs_patch1.o -i /lib/shiva -s /opt/shiva/modules -o core-cpu1.patched
The Shiva install script installs all of the patch modules into /opt/shiva/modules
The patch build environments are stored in modules/aarch64_patches/ and are as follows:
This is just a simple patch that uses symbol interposition to replace the
STB_GLOBAL/STT_FUNC OS_printf that lives within the core-cpu1 executable.
The patch cfs_patch1.c simply rewrites its own version of the function.
The contents of the ./modules/aarch64_patches/cfs_patch1
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ ls
cfs_patch1.c cfs_patch1.o core-cpu1 core-cpu1.patched EEPROM.DAT Makefile
The program that we are patching is core-cpu1 and specifically the symbol OS_printf
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ readelf -s core-cpu1 | grep OS_printf
241: 0000000000047d88 456 FUNC GLOBAL DEFAULT 13 OS_printf
Our patch contains it's own version of the function OS_printf and at runtime Shiva will load
the /opt/shiva/modules/cfs_patch1.o handle all of it's own relocations, and then it will externally
re-link core-cpu1 so that any calls to the old OS_printf are patched to call the new OS_printf
that lives within the modules runtime environment setup by Shiva.
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ cat cfs_patch1.c
#include <stdarg.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
void OS_printf(const char *string, ...)
{
char msg_buffer[4096];
va_list va;
int sz;
va_start(va, string);
sz = vsnprintf(msg_buffer, sizeof(msg_buffer), string, va);
va_end(va);
msg_buffer[sz] = '\0';
printf("[PATCHED :)]: %s\n", msg_buffer); /* NOTICE THIS LINE */
}
A quick look at the PT_INTERP segment will reveal that core-cpu1.patched has "/lib/shiva"
set as the program interpreter.
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ readelf -l core-cpu1.patched | grep interpreter
[Requesting program interpreter: /lib/shiva]
Two custom dynamic segment entries were also added to the binary:
SHIVA_DT_SEARCH denotes a dynamic entry containing the address of the module search path,
usually set to "/opt/shiva/modules/".
SHIVA_DT_NEEDED denotes a dynamic entry containing the address of the module basename,
i.e. "cfs_patch1.o".
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ readelf -d core-cpu1.patched | tail -n 3
0x0000000060000018 (Operating System specific: 60000018) 0x1ab200
0x0000000060000017 (Operating System specific: 60000017) 0x1ab213
0x0000000000000000 (NULL) 0x0
NOTE: The new dynamic segment lives within a newly created PT_LOAD segment. The new PT_LOAD segment is the result of a PT_NOTE to PT_LOAD transition.
When running the ./core-cpu.patched we see in the last stdout line our patched
OS_printf executes. Notice it prefaces each line of output with the string "[PATCHED :)]"
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/cfs_patch1$ ./core-cpu1.patched
OS_BSP_Initialize():Maximum user msg queue depth = 10
CFE_PSP: Default Reset SubType = 1
CFE_PSP: Default CPU ID = 1
CFE_PSP: Default Spacecraft ID = 66
CFE_PSP: Default CPU Name: cpu1
OS_Posix_GetSchedulerParams():186:Policy 1: available, min-max: 1-99
OS_Posix_GetSchedulerParams():186:Policy 2: available, min-max: 1-99
OS_Posix_TaskAPI_Impl_Init():372:Selected policy 2 for RT tasks, root task = 99
OS_Posix_TaskAPI_Impl_Init():388:Could not setschedparam in main thread: Operation not permitted (1)
CFE_PSP: initializing module 'soft_timebase' with ID 0110ff00
CFE_PSP: Instantiated software timebase 'cFS-Master' running at 10000 usec
CFE_PSP: initializing module 'timebase_posix_clock' with ID 0110ff01
CFE_PSP: Using POSIX monotonic clock as CFE timebase
CFE_PSP: initializing module 'eeprom_mmap_file' with ID 0110ff02
CFE_PSP: Using MMAP simulated EEPROM implementation
[PATCHED :)]: CFE_PSP: EEPROM Range (2) created: Start Address = FFFF84032000, Size = 00080000 Status = 0
modules/aarch64_patches/rodata_interposing
This patch demonstrates how Shiva is able to link new read-only data into place over existing read-only data symbols. For example
The contents of the rodata_interposing directory
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$ ls
Makefile ro_patch.c ro_patch.o test_rodata test_rodata.c test_rodata.patched
The original program has a read-only string const char rodata_string[] = "Arcana Technologies"
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$ readelf -s test_rodata | grep rodata_string
73: 0000000000000800 20 OBJECT GLOBAL DEFAULT 15 rodata_string
This constant string data is stored within the .rodata section.
objdump -D test_rodata | less
...
0000000000000800 <rodata_string>:
800: 61637241 .word 0x61637241
804: 5420616e .word 0x5420616e
808: 6e686365 .word 0x6e686365
80c: 676f6c6f .word 0x676f6c6f
810: 00736569 .word 0x00736569
Our patch aims to change the string from "Arcana Technologies" to "The Great Arcanum".
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$ cat ro_patch.c
const char rodata_string[] = "The Great Arcanum";
The compiled patch is ro_patch.o
At runtime Shiva will load and link the patch with the executable in memory, and all references
to the old rodata_string[] will be replaced with the correct offset to the patches version of
rodata_string[]. The original string is not being over-written, but is no longer referenced.
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$ ./test_rodata
rodata_string: Arcana Technologies
val: 5
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$ ./test_rodata.patched
rodata_string: The Great Arcanum
val: 5
elfmaster@esoteric-aarch64:~/amp/shiva/modules/aarch64_patches/rodata_interposing$
Read the user manual. https://github.com/advanced-microcode-patching/shiva_user_manual
Ryan O'Neill ryan@bitlackeys.org