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Kernel: Add an extremely primitive version of KASLR

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This initial (and very basic) implementation of KASLR simply randomizes
the kernel base VA in the 256 MiB range following the default load base.
This commit is contained in:
Idan Horowitz 2022-03-21 22:59:48 +02:00 • committed by Andreas Kling
parent a9764dabee
commit 1ad0e05ea1
Notes: sideshowbarker 2024-07-17 16:58:30 +09:00
1 changed files with 37 additions and 1 deletions
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38
Kernel/Prekernel/init.cpp
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@ -14,6 +14,11 @@
#include <LibC/elf.h>
#include <LibELF/Relocation.h>
#if ARCH(I386) || ARCH(X86_64)
# include <Kernel/Arch/x86/ASM_wrapper.h>
# include <Kernel/Arch/x86/CPUID.h>
#endif
// Defined in the linker script
extern size_t __stack_chk_guard;
size_t __stack_chk_guard __attribute__((used));
@ -67,6 +72,8 @@ extern "C" [[noreturn]] void init();
// This is where C++ execution begins, after boot.S transfers control here.
//
u64 generate_secure_seed();
extern "C" [[noreturn]] void init()
{
if (multiboot_info_ptr->mods_count < 1)
@ -88,6 +95,10 @@ extern "C" [[noreturn]] void init()
#else
FlatPtr kernel_load_base = 0x2000200000;
#endif
// KASLR
static constexpr auto maximum_offset = 256 * MiB;
kernel_load_base = kernel_load_base + (generate_secure_seed() % maximum_offset);
kernel_load_base = kernel_load_base & ~(PAGE_SIZE - 1);
FlatPtr kernel_load_end = 0;
for (size_t i = 0; i < kernel_elf_header.e_phnum; i++) {
@ -201,7 +212,7 @@ extern "C" [[noreturn]] void init()
#if ARCH(I386)
"add %0, %%esp"
#else
"movabs %0, %%rax\n"
"mov %0, %%rax\n"
"add %%rax, %%rsp"
#endif
::"g"(kernel_mapping_base)
@ -225,6 +236,31 @@ extern "C" [[noreturn]] void init()
__builtin_unreachable();
}
u64 generate_secure_seed()
{
u32 seed = 0xFEEBDAED;
#if ARCH(I386) || ARCH(X86_64)
CPUID processor_info(0x1);
if (processor_info.edx() & (1 << 4)) // TSC
seed ^= read_tsc();
if (processor_info.ecx() & (1 << 30)) // RDRAND
seed ^= rdrand();
CPUID extended_features(0x7);
if (extended_features.ebx() & (1 << 18)) // RDSEED
seed ^= rdseed();
#else
# warning No native randomness source available for this architecture
#endif
seed ^= multiboot_info_ptr->mods_addr;
seed ^= multiboot_info_ptr->framebuffer_addr;
return seed;
}
// Define some Itanium C++ ABI methods to stop the linker from complaining.
// If we actually call these something has gone horribly wrong
void* __dso_handle __attribute__((visibility("hidden")));