mia: improve CIC detection algorithm #1296
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invertego
reviewed
Nov 20, 2023
mia/medium/nintendo-64.cpp
Outdated
| auto Nintendo64::ipl2checksum(u32 seed, array_view<u8> rom) -> u64 | ||
| { | ||
| auto rotl = [](u32 value, u32 shift) -> u32 { | ||
| return (value << shift) | (value >> (32 - shift)); |
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Shifting a u32 by 32 bits is UB. Same for rotr.
Might be good to move the rotate helpers to nall/bit.hpp. We can eventually just switch to the C++ standard library implementation when we move to C++20.
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Done, but I don't want to move it to nall as I don't want to think now how to make that a template.
invertego
reviewed
Nov 21, 2023
mia/medium/nintendo-64.cpp
Outdated
| while (1) { | ||
| loop++; | ||
| dataLast = data; | ||
| data = read(dataIndex); |
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FYI, array_view has a built-in helper for big endian reads.
data = rom.readm(4);
rom += 4;
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Done, though readm already advances the pointer
mia/medium/nintendo-64.cpp
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| }; | ||
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| auto Nintendo64::ipl2checksum(u32 seed, array_view<u8> rom) -> u64 | ||
| { |
mia/medium/nintendo-64.cpp
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| for (auto &b : buf) b = state[0]; | ||
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| for (loop = 0; loop < 16; loop++) | ||
| { |
Currently, we detect the CIC to emulate by calculating a CRC32 over IPL3 bootcode in ROM, and keeping a database of the known IPL3s. This works because right now there are only a handful of IPL3 variants (exactly one per CIC). In preparation for libdragon releasing an open source IPL3 that could evolve and be forked an unbounded number of times, we must stop keeping a database of IPL3s. This commit changes strategy: it simulates the IPL2 checksum hash over IPL3 (which is exactly what a real N64 does at boot) and verifies if the checksum matches that expected by any of the known CIC variants. This works because open source IPL3 variants must anyway have a checksum that collides with that of CICs (which must be obtained via a second preimage attack, bruteforced on GPUs), otherwise they would not work on real hardware nor on Ares itself (which correctly simulates the boot sequence and would refuse to boot an "unsigned" IPL3).
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Currently, we detect the CIC to emulate by calculating a CRC32 over IPL3 bootcode in ROM, and keeping a database of the known IPL3s. This works because right now there are only a handful of IPL3 variants (exactly one per CIC).
In preparation for libdragon releasing an open source IPL3 that could evolve and be forked an unbounded number of times, we must stop keeping a database of IPL3s.
This commit changes strategy: it simulates the IPL2 checksum hash over IPL3 (which is exactly what a real N64 does at boot) and verifies if the checksum matches that expected by any of the known CIC variants. This works because open source IPL3 variants must anyway have a checksum that collides with that of CICs (which must be obtained via a second preimage attack, bruteforced on GPUs), otherwise they would not work on real hardware nor on Ares itself (which correctly simulates the boot sequence and would refuse to boot an "unsigned" IPL3).