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Atmosphere/mesosphere/kernel_ldr/source/kern_init_loader.cpp

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C++

/*
* 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 <mesosphere.hpp>
#include "kern_init_loader_board_setup.hpp"
/* Necessary for calculating kernelldr size/base for initial identity mapping */
extern "C" {
extern const u8 __start__[];
extern const u8 __end__[];
}
namespace ams::kern::init::loader {
namespace {
constexpr uintptr_t KernelBaseAlignment = 0x200000;
constexpr uintptr_t KernelBaseRangeStart = 0xFFFFFF8000000000;
constexpr uintptr_t KernelBaseRangeEnd = 0xFFFFFFFFFFE00000;
constexpr uintptr_t KernelBaseRangeLast = KernelBaseRangeEnd - 1;
static_assert(util::IsAligned(KernelBaseRangeStart, KernelBaseAlignment));
static_assert(util::IsAligned(KernelBaseRangeEnd, KernelBaseAlignment));
static_assert(KernelBaseRangeStart <= KernelBaseRangeLast);
static_assert(InitialProcessBinarySizeMax <= KernelResourceSize);
constexpr size_t InitialPageTableRegionSizeMax = 2_MB;
static_assert(InitialPageTableRegionSizeMax < KernelPageTableHeapSize + KernelInitialPageHeapSize);
/* Global Allocator. */
constinit KInitialPageAllocator g_initial_page_allocator;
constinit KInitialPageAllocator::State g_final_page_allocator_state;
constinit InitialProcessBinaryLayout g_initial_process_binary_layout;
constinit void *g_final_state[2];
void RelocateKernelPhysically(uintptr_t &base_address, KernelLayout *&layout) {
KPhysicalAddress correct_base = KSystemControl::Init::GetKernelPhysicalBaseAddress(base_address);
if (correct_base != base_address) {
const uintptr_t diff = GetInteger(correct_base) - base_address;
const size_t size = layout->rw_end_offset;
/* Conversion from KPhysicalAddress to void * is safe here, because MMU is not set up yet. */
std::memmove(reinterpret_cast<void *>(GetInteger(correct_base)), reinterpret_cast<void *>(base_address), size);
base_address += diff;
layout = reinterpret_cast<KernelLayout *>(reinterpret_cast<uintptr_t>(layout) + diff);
}
}
void SetupInitialIdentityMapping(KInitialPageTable &init_pt, uintptr_t base_address, uintptr_t kernel_size, uintptr_t page_table_region, size_t page_table_region_size, KInitialPageTable::PageAllocator &allocator) {
/* Map in an RWX identity mapping for the kernel. */
constexpr PageTableEntry KernelRWXIdentityAttribute(PageTableEntry::Permission_KernelRWX, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
init_pt.Map(base_address, kernel_size, base_address, KernelRWXIdentityAttribute, allocator);
/* Map in an RWX identity mapping for ourselves. */
constexpr PageTableEntry KernelLdrRWXIdentityAttribute(PageTableEntry::Permission_KernelRWX, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
const uintptr_t kernel_ldr_base = util::AlignDown(reinterpret_cast<uintptr_t>(__start__), PageSize);
const uintptr_t kernel_ldr_size = util::AlignUp(reinterpret_cast<uintptr_t>(__end__), PageSize) - kernel_ldr_base;
init_pt.Map(kernel_ldr_base, kernel_ldr_size, kernel_ldr_base, KernelRWXIdentityAttribute, allocator);
/* Map in the page table region as RW- for ourselves. */
constexpr PageTableEntry PageTableRegionRWAttribute(PageTableEntry::Permission_KernelRW, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
init_pt.Map(page_table_region, page_table_region_size, page_table_region, KernelRWXIdentityAttribute, allocator);
/* Place the L1 table addresses in the relevant system registers. */
cpu::SetTtbr0El1(init_pt.GetTtbr0L1TableAddress());
cpu::SetTtbr1El1(init_pt.GetTtbr1L1TableAddress());
/* Setup MAIR_EL1, TCR_EL1. */
/* TODO: Define these bits properly elsewhere, document exactly what each bit set is doing .*/
constexpr u64 MairValue = 0x0000000044FF0400ul;
constexpr u64 TcrValue = 0x00000011B5193519ul;
cpu::MemoryAccessIndirectionRegisterAccessor(MairValue).Store();
cpu::TranslationControlRegisterAccessor(TcrValue).Store();
/* Perform board-specific setup. */
PerformBoardSpecificSetup();
/* Ensure that the entire cache is flushed. */
cpu::FlushEntireCacheForInit();
/* Setup SCTLR_EL1. */
/* TODO: Define these bits properly elsewhere, document exactly what each bit set is doing .*/
constexpr u64 SctlrValue = 0x0000000034D5D925ul;
cpu::SetSctlrEl1(SctlrValue);
cpu::EnsureInstructionConsistency();
}
KVirtualAddress GetRandomKernelBaseAddress(KInitialPageTable &page_table, KPhysicalAddress phys_base_address, size_t kernel_size) {
/* Define useful values for random generation. */
const uintptr_t kernel_offset = GetInteger(phys_base_address) % KernelBaseAlignment;
/* Repeatedly generate a random virtual address until we get one that's unmapped in the destination page table. */
while (true) {
const uintptr_t random_kaslr_slide = KSystemControl::Init::GenerateRandomRange(KernelBaseRangeStart / KernelBaseAlignment, KernelBaseRangeLast / KernelBaseAlignment);
const KVirtualAddress kernel_region_start = random_kaslr_slide * KernelBaseAlignment;
const KVirtualAddress kernel_region_end = kernel_region_start + util::AlignUp(kernel_offset + kernel_size, KernelBaseAlignment);
const size_t kernel_region_size = GetInteger(kernel_region_end) - GetInteger(kernel_region_start);
/* Make sure the region has not overflowed */
if (kernel_region_start >= kernel_region_end) {
continue;
}
/* Make sure that the region stays within our intended bounds. */
if (kernel_region_end > KernelBaseRangeEnd) {
continue;
}
/* Validate we can map the range we've selected. */
if (!page_table.IsFree(kernel_region_start, kernel_region_size)) {
continue;
}
/* Our range is valid! */
return kernel_region_start + kernel_offset;
}
}
}
uintptr_t Main(uintptr_t base_address, KernelLayout *layout, uintptr_t ini_base_address) {
/* Relocate the kernel to the correct physical base address. */
/* Base address and layout are passed by reference and modified. */
RelocateKernelPhysically(base_address, layout);
/* Validate kernel layout. */
const uintptr_t rx_offset = layout->rx_offset;
const uintptr_t rx_end_offset = layout->rx_end_offset;
const uintptr_t ro_offset = layout->ro_offset;
const uintptr_t ro_end_offset = layout->ro_end_offset;
const uintptr_t rw_offset = layout->rw_offset;
/* UNUSED: const uintptr_t rw_end_offset = layout->rw_end_offset; */
const uintptr_t bss_end_offset = layout->bss_end_offset;
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(rx_offset, PageSize));
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(rx_end_offset, PageSize));
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(ro_offset, PageSize));
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(ro_end_offset, PageSize));
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(rw_offset, PageSize));
MESOSPHERE_INIT_ABORT_UNLESS(util::IsAligned(bss_end_offset, PageSize));
const uintptr_t bss_offset = layout->bss_offset;
const uintptr_t resource_offset = layout->resource_offset;
const uintptr_t dynamic_offset = layout->dynamic_offset;
const uintptr_t init_array_offset = layout->init_array_offset;
const uintptr_t init_array_end_offset = layout->init_array_end_offset;
/* Determine the size of the resource region. */
const size_t resource_region_size = KMemoryLayout::GetResourceRegionSizeForInit();
const uintptr_t resource_end_address = base_address + resource_offset + resource_region_size;
/* Setup the INI1 header in memory for the kernel. */
KSystemControl::Init::GetInitialProcessBinaryLayout(std::addressof(g_initial_process_binary_layout));
MESOSPHERE_INIT_ABORT_UNLESS(g_initial_process_binary_layout.address != 0);
if (ini_base_address != g_initial_process_binary_layout.address) {
/* The INI is not at the correct address, so we need to relocate it. */
const InitialProcessBinaryHeader *ini_header = reinterpret_cast<const InitialProcessBinaryHeader *>(ini_base_address);
if (ini_header->magic == InitialProcessBinaryMagic && ini_header->size <= InitialProcessBinarySizeMax) {
/* INI is valid, relocate it. */
std::memmove(reinterpret_cast<void *>(g_initial_process_binary_layout.address), ini_header, ini_header->size);
} else {
/* INI is invalid. Make the destination header invalid. */
std::memset(reinterpret_cast<void *>(g_initial_process_binary_layout.address), 0, sizeof(InitialProcessBinaryHeader));
}
}
/* We want to start allocating page tables at the end of the resource region. */
g_initial_page_allocator.Initialize(resource_end_address);
/* Make a new page table for TTBR1_EL1. */
KInitialPageTable init_pt(KernelBaseRangeStart, KernelBaseRangeLast, g_initial_page_allocator);
/* Setup initial identity mapping. TTBR1 table passed by reference. */
SetupInitialIdentityMapping(init_pt, base_address, bss_end_offset, resource_end_address, InitialPageTableRegionSizeMax, g_initial_page_allocator);
/* Generate a random slide for the kernel's base address. */
const KVirtualAddress virtual_base_address = GetRandomKernelBaseAddress(init_pt, base_address, bss_end_offset);
/* Map kernel .text as R-X. */
constexpr PageTableEntry KernelTextAttribute(PageTableEntry::Permission_KernelRX, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
init_pt.Map(virtual_base_address + rx_offset, rx_end_offset - rx_offset, base_address + rx_offset, KernelTextAttribute, g_initial_page_allocator);
/* Map kernel .rodata and .rwdata as RW-. */
/* Note that we will later reprotect .rodata as R-- */
constexpr PageTableEntry KernelRoDataAttribute(PageTableEntry::Permission_KernelR, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
constexpr PageTableEntry KernelRwDataAttribute(PageTableEntry::Permission_KernelRW, PageTableEntry::PageAttribute_NormalMemory, PageTableEntry::Shareable_InnerShareable, PageTableEntry::MappingFlag_Mapped);
init_pt.Map(virtual_base_address + ro_offset, ro_end_offset - ro_offset, base_address + ro_offset, KernelRwDataAttribute, g_initial_page_allocator);
init_pt.Map(virtual_base_address + rw_offset, bss_end_offset - rw_offset, base_address + rw_offset, KernelRwDataAttribute, g_initial_page_allocator);
/* Physically randomize the kernel region. */
/* NOTE: Nintendo does this only on 10.0.0+ */
init_pt.PhysicallyRandomize(virtual_base_address + rx_offset, bss_end_offset - rx_offset, true);
/* Apply relocations to the kernel. */
const Elf::Dyn *kernel_dynamic = reinterpret_cast<const Elf::Dyn *>(GetInteger(virtual_base_address) + dynamic_offset);
Elf::ApplyRelocations(GetInteger(virtual_base_address), kernel_dynamic);
/* Clear kernel .bss. */
/* NOTE: The kernel does this before applying relocations, but we do it after. */
/* This allows us to place our relocations in space overlapping with .bss...and thereby reclaim the memory that would otherwise be wasted. */
std::memset(GetVoidPointer(virtual_base_address + bss_offset), 0, bss_end_offset - bss_offset);
/* Call the kernel's init array functions. */
/* NOTE: The kernel does this after reprotecting .rodata, but we do it before. */
/* This allows our global constructors to edit .rodata, which is valuable for editing the SVC tables to support older firmwares' ABIs. */
Elf::CallInitArrayFuncs(GetInteger(virtual_base_address) + init_array_offset, GetInteger(virtual_base_address) + init_array_end_offset);
/* Reprotect .rodata as R-- */
init_pt.Reprotect(virtual_base_address + ro_offset, ro_end_offset - ro_offset, KernelRwDataAttribute, KernelRoDataAttribute);
/* Return the difference between the random virtual base and the physical base. */
return GetInteger(virtual_base_address) - base_address;
}
KPhysicalAddress AllocateKernelInitStack() {
return g_initial_page_allocator.Allocate(PageSize) + PageSize;
}
void **GetFinalState() {
/* Get final page allocator state. */
g_initial_page_allocator.GetFinalState(std::addressof(g_final_page_allocator_state));
/* Setup final kernel loader state. */
g_final_state[0] = std::addressof(g_final_page_allocator_state);
g_final_state[1] = std::addressof(g_initial_process_binary_layout);
return g_final_state;
}
}