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kern: implement additional randomness in KPageHeap allocations

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This commit is contained in:
Michael Scire 2022-03-22 15:29:55 -07:00 • committed by SciresM
parent 24739f245e
commit 401047f603
6 changed files with 150 additions and 18 deletions
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46
libraries/libmesosphere/include/mesosphere/kern_k_page_bitmap.hpp
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@ -20,7 +20,7 @@
namespace ams::kern {
class KPageBitmap {
private:
public:
class RandomBitGenerator {
private:
util::TinyMT m_rng;
@ -42,12 +42,43 @@ namespace ams::kern {
--m_bits_available;
return rnd_bit;
}
u64 GenerateRandomBits(u32 num_bits) {
u64 result = 0;
/* Iteratively add random bits to our result. */
while (num_bits > 0) {
/* Ensure we have random bits to take from. */
if (m_bits_available == 0) {
this->RefreshEntropy();
}
/* Determine how many bits to take this round. */
const auto cur_bits = std::min(num_bits, m_bits_available);
/* Generate mask for our current bits. */
const u64 mask = (static_cast<u64>(1) << cur_bits) - 1;
/* Add bits to output from our entropy. */
result <<= cur_bits;
result |= (m_entropy & mask);
/* Remove bits from our entropy. */
m_entropy >>= cur_bits;
m_bits_available -= cur_bits;
/* Advance. */
num_bits -= cur_bits;
}
return result;
}
public:
RandomBitGenerator() : m_entropy(), m_bits_available() {
m_rng.Initialize(static_cast<u32>(KSystemControl::GenerateRandomU64()));
}
size_t SelectRandomBit(u64 bitmap) {
u64 SelectRandomBit(u64 bitmap) {
u64 selected = 0;
for (size_t cur_num_bits = BITSIZEOF(bitmap) / 2; cur_num_bits != 0; cur_num_bits /= 2) {
@ -66,6 +97,17 @@ namespace ams::kern {
return selected;
}
u64 GenerateRandom(u64 max) {
/* Determine the number of bits we need. */
const u64 bits_needed = 1 + (BITSIZEOF(max) - util::CountLeadingZeros(max));
/* Generate a random value of the desired bitwidth. */
const u64 rnd = this->GenerateRandomBits(bits_needed);
/* Adjust the value to be in range. */
return rnd - ((rnd / max) * max);
}
};
public:
static constexpr size_t MaxDepth = 4;