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Kernel: Validate x86_64 address canonicality before SafeMem operations

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This ensures we don't GP on x86_64 when a non-canonical address is fed
to a safe_foo() operation.
This commit is contained in:
Idan Horowitz 2021-10-04 23:42:10 +03:00 • committed by Andreas Kling
parent cd975668d6
commit ce334ee1bc
1 changed files with 29 additions and 0 deletions
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29
Kernel/Arch/x86/common/SafeMem.cpp
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@ -4,6 +4,7 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/Arch/x86/Processor.h>
#include <Kernel/Arch/x86/RegisterState.h>
#include <Kernel/Arch/x86/SafeMem.h>
@ -39,12 +40,32 @@ extern "C" u8 safe_atomic_compare_exchange_relaxed_faulted[];
namespace Kernel {
ALWAYS_INLINE bool validate_canonical_address(size_t address)
{
#if ARCH(X86_64)
auto most_significant_bits = Processor::current().virtual_address_bit_width() - 1;
auto insignificant_bits = address >> most_significant_bits;
return insignificant_bits == 0 || insignificant_bits == (0xffffffffffffffffull >> most_significant_bits);
#else
(void)address;
return true;
#endif
}
CODE_SECTION(".text.safemem")
NEVER_INLINE bool safe_memcpy(void* dest_ptr, const void* src_ptr, size_t n, void*& fault_at)
{
fault_at = nullptr;
size_t dest = (size_t)dest_ptr;
if (!validate_canonical_address(dest)) {
fault_at = dest_ptr;
return false;
}
size_t src = (size_t)src_ptr;
if (!validate_canonical_address(src)) {
fault_at = const_cast<void*>(src_ptr);
return false;
}
size_t remainder;
// FIXME: Support starting at an unaligned address.
if (!(dest & 0x3) && !(src & 0x3) && n >= 12) {
@ -96,6 +117,10 @@ NEVER_INLINE bool safe_memcpy(void* dest_ptr, const void* src_ptr, size_t n, voi
CODE_SECTION(".text.safemem")
NEVER_INLINE ssize_t safe_strnlen(const char* str, size_t max_n, void*& fault_at)
{
if (!validate_canonical_address((size_t)str)) {
fault_at = const_cast<char*>(str);
return false;
}
ssize_t count = 0;
fault_at = nullptr;
asm volatile(
@ -129,6 +154,10 @@ NEVER_INLINE bool safe_memset(void* dest_ptr, int c, size_t n, void*& fault_at)
{
fault_at = nullptr;
size_t dest = (size_t)dest_ptr;
if (!validate_canonical_address(dest)) {
fault_at = dest_ptr;
return false;
}
size_t remainder;
// FIXME: Support starting at an unaligned address.
if (!(dest & 0x3) && n >= 12) {