invoxiplaygames.uk
UEFI utility to spoof the brand string of modern AMD processors via Machine State Registers. (Mirrored from https://github.com/InvoxiPlayGames/amd-brand-string-edit )
1#![no_main]
2#![no_std]
3
4// CHANGE ME!
5// new brand string must be EXACTLY 48 characters (pad with spaces)
6static NEW_BRAND_STRING: &'static str = "Lappy 486 ";
7// 48 character reference: ------------------------------------------------
8
9use uefi::print;
10use uefi::prelude::*;
11use x86::cpuid::CpuId;
12use core::arch::asm;
13use core::convert::TryInto;
14
15unsafe fn wrmsr_amd(msr: u32, value: u64) {
16 let low = value as u32;
17 let high = (value >> 32) as u32;
18 // wrmsr with the AMD "secret" key - not necessary for these MSRs
19 let secret = 0x9c5a203a as u32;
20 unsafe {
21 asm!("wrmsr", in("ecx") msr, in("eax") low, in("edx") high, in("edi") secret);
22 }
23}
24
25pub fn brand_string_to_int64(brand_str: &str) -> Option<[u64; 6]> {
26 // make sure we have exactly 48 characters for the brand string
27 if brand_str.len() != 48 {
28 return None
29 }
30 let str_bytes = brand_str.as_bytes();
31 let mut out = [0u64; 6];
32 // convert it to an array of 6 LE integers
33 // does rust seriously not support for loops
34 let mut i = 0;
35 while i < 6 {
36 let start = i * 8;
37 let chunk: [u8; 8] = str_bytes[start..start + 8].try_into().unwrap();
38 out[i] = u64::from_le_bytes(chunk);
39 i += 1;
40 }
41 Some(out)
42}
43
44#[entry]
45fn main() -> Status {
46 uefi::helpers::init().unwrap();
47 // get the vendor (we only work on AMD)
48 let cpu_id = CpuId::new();
49 let vendor_name = cpu_id.get_vendor_info().unwrap();
50 print!("CPU vendor: {}\n", vendor_name.as_str());
51 if vendor_name.as_str() == "AuthenticAMD" {
52 // get the current CPU brand string
53 let old_brand_string = cpu_id.get_processor_brand_string().unwrap();
54 print!("Current brand: \"{}\"\n", old_brand_string.as_str());
55 // convert to integers to set in the MSRs
56 match brand_string_to_int64(NEW_BRAND_STRING) {
57 None => print!("Invalid format for brand string\n\"{}\".\n", NEW_BRAND_STRING),
58 Some(ints) => {
59 // set the Core::X86::Msr::ProcNameString registers to our new string
60 let mut i = 0;
61 while i < 6 {
62 unsafe {
63 wrmsr_amd(0xC0010030 + i, ints[i as usize]);
64 }
65 i += 1;
66 }
67 // verify that the string has actually changed
68 let verify_brand_string = cpu_id.get_processor_brand_string().unwrap();
69 print!("New brand: \"{}\"\n", verify_brand_string.as_str());
70 }
71 }
72 } else {
73 print!("This program only supports AuthenticAMD.\n");
74 }
75 // stall for 7 seconds to let you read the console output
76 boot::stall(7_000_000);
77 Status::SUCCESS
78}