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Atmosphere/exosphere/program/source/smc/secmon_random_cache.cpp

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/*
* Copyright (c) Atmosphère-NX
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <exosphere.hpp>
#include "secmon_smc_common.hpp"
#include "secmon_random_cache.hpp"
namespace ams::secmon::smc {
namespace {
constinit int g_random_offset_low = 0;
constinit int g_random_offset_high = 0;
void FillRandomCache(int offset, int size) {
/* Get the cache. */
u8 * const random_cache_loc = GetRandomBytesCache() + offset;
/* Flush the region we're about to fill to ensure consistency with the SE. */
hw::FlushDataCache(random_cache_loc, size);
hw::DataSynchronizationBarrierInnerShareable();
/* Generate random bytes. */
se::GenerateRandomBytes(random_cache_loc, size);
hw::DataSynchronizationBarrierInnerShareable();
/* Flush to ensure the CPU sees consistent data for the region. */
hw::FlushDataCache(random_cache_loc, size);
hw::DataSynchronizationBarrierInnerShareable();
}
}
void FillRandomCache() {
/* Fill the cache. */
FillRandomCache(0, GetRandomBytesCacheSize());
/* Set the extents. */
g_random_offset_low = 0;
g_random_offset_high = GetRandomBytesCacheSize() - 1;
}
void RefillRandomCache() {
/* Check that we need to do any refilling. */
if (const int used_start = (g_random_offset_high + 1) % GetRandomBytesCacheSize(); used_start != g_random_offset_low) {
if (used_start < g_random_offset_low) {
/* The region we need to fill is after used_start but before g_random_offset_low. */
const auto size = g_random_offset_low - used_start;
FillRandomCache(used_start, size);
g_random_offset_high += size;
} else {
/* We need to fill the space from high to the end and from low to start. */
const int high_size = GetRandomBytesCacheSize() - used_start;
if (high_size > 0) {
FillRandomCache(used_start, high_size);
g_random_offset_high += high_size;
}
const int low_size = g_random_offset_low;
if (low_size > 0) {
FillRandomCache(0, low_size);
g_random_offset_high += low_size;
}
}
g_random_offset_high %= GetRandomBytesCacheSize();
}
}
void GetRandomFromCache(void *dst, size_t size) {
/* Copy out the requested size. */
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std::memcpy(dst, GetRandomBytesCache() + g_random_offset_low, size);
/* Advance. */
g_random_offset_low += size;
/* Ensure that at all times g_random_offset_low is not within 0x38 bytes of the end of the pool. */
if (g_random_offset_low + MaxRandomBytes >= GetRandomBytesCacheSize()) {
g_random_offset_low = 0;
}
}
}