LuaJIT script to read Linux kernel memory in ARM architecture using /dev/mem

memread.lua

local ffi = require("ffi")
local C = ffi.C
ffi.cdef[[
static const int O_RDONLY = 0;
static const int SEEK_SET = 0;
int open(const char *, int, ...);
int close(int);
long int lseek(int, long int, int) __attribute__((__nothrow__, __leaf__));
int read(int, void *, unsigned int);
]]
function getVar(var_pattern)
	local page_offset, phys_start, var_addr, value
	for line in io.lines("/proc/kallsyms") do
		local addr, symb = line:match("^(%x+) [^ ]+ (.+)$")
		if symb == "_stext" then
			page_offset = tonumber(addr, 16) - 0x8000  -- see arch/arm/kernel/ldlinux.lds
		elseif symb and symb:match(var_pattern) then
			var_addr = tonumber(addr, 16)
			break
		end
	end
	for line in io.lines("/proc/iomem") do
		phys_start = line:match("^(%x+)-%x+ : System RAM")
		if phys_start then
			phys_start = tonumber(phys_start, 16)
			break
		end
	end
	if var_addr and page_offset and phys_start then
		local data = ffi.new("int[1]")
		local fd = C.open("/dev/mem", C.O_RDONLY)
		C.lseek(fd, var_addr + phys_start - page_offset, C.SEEK_SET)
		if C.read(fd, data, ffi.sizeof(data)) ~= -1 then
			value = data[0]
		end
		C.close(fd)
	end
	return value
end
print(bit.tohex(getVar("getpid")))
print(bit.tohex(getVar("^last_FL_duty")))