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refactor: standardize obfuscation memory alignment

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See:
* https://github.com/bitcoin/bitcoin/pull/31144#discussion_r2216962117
* https://github.com/bitcoin/bitcoin/pull/31144#discussion_r2220277161
* https://github.com/bitcoin/bitcoin/pull/31144#discussion_r2210851772

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
This commit is contained in:
Lőrinc
2025-07-22 10:15:46 -07:00
parent 13f00345c0
commit 86e3a0a8cb
1 changed files with 5 additions and 5 deletions
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10
src/util/obfuscation.h
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@@ -36,21 +36,21 @@ public:
KeyType rot_key{m_rotations[key_offset % KEY_SIZE]}; // Continue obfuscation from where we left off KeyType rot_key{m_rotations[key_offset % KEY_SIZE]}; // Continue obfuscation from where we left off
if (target.size() > KEY_SIZE) { if (target.size() > KEY_SIZE) {
// Obfuscate until 64-bit alignment boundary // Obfuscate until KEY_SIZE alignment boundary
if (const auto misalign{std::bit_cast<uintptr_t>(target.data()) % KEY_SIZE}) { if (const auto misalign{reinterpret_cast<uintptr_t>(target.data()) % KEY_SIZE}) {
const size_t alignment{std::min(KEY_SIZE - misalign, target.size())}; const size_t alignment{KEY_SIZE - misalign};
XorWord(target.first(alignment), rot_key); XorWord(target.first(alignment), rot_key);
target = {std::assume_aligned<KEY_SIZE>(target.data() + alignment), target.size() - alignment}; target = {std::assume_aligned<KEY_SIZE>(target.data() + alignment), target.size() - alignment};
rot_key = m_rotations[(key_offset + alignment) % KEY_SIZE]; rot_key = m_rotations[(key_offset + alignment) % KEY_SIZE];
} }
// Aligned obfuscation in 64-byte chunks // Aligned obfuscation in 8*KEY_SIZE chunks
for (constexpr auto unroll{8}; target.size() >= KEY_SIZE * unroll; target = target.subspan(KEY_SIZE * unroll)) { for (constexpr auto unroll{8}; target.size() >= KEY_SIZE * unroll; target = target.subspan(KEY_SIZE * unroll)) {
for (size_t i{0}; i < unroll; ++i) { for (size_t i{0}; i < unroll; ++i) {
XorWord(target.subspan(i * KEY_SIZE, KEY_SIZE), rot_key); XorWord(target.subspan(i * KEY_SIZE, KEY_SIZE), rot_key);
} }
} }
// Aligned obfuscation in 64-bit chunks // Aligned obfuscation in KEY_SIZE chunks
for (; target.size() >= KEY_SIZE; target = target.subspan(KEY_SIZE)) { for (; target.size() >= KEY_SIZE; target = target.subspan(KEY_SIZE)) {
XorWord(target.first<KEY_SIZE>(), rot_key); XorWord(target.first<KEY_SIZE>(), rot_key);
} }