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/* SPDX-License-Identifier: GPL-2.0 */
/*
* x86 KMSAN support.
*
* Copyright (C) 2022, Google LLC
* Author: Alexander Potapenko <[email protected]>
*/
#ifndef _ASM_X86_KMSAN_H
#define _ASM_X86_KMSAN_H
#ifndef MODULE
#include <asm/cpu_entry_area.h>
#include <asm/processor.h>
#include <linux/mmzone.h>
DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_origin);
/*
* Functions below are declared in the header to make sure they are inlined.
* They all are called from kmsan_get_metadata() for every memory access in
* the kernel, so speed is important here.
*/
/*
* Compute metadata addresses for the CPU entry area on x86.
*/
static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
{
unsigned long addr64 = (unsigned long)addr;
char *metadata_array;
unsigned long off;
int cpu;
if ((addr64 < CPU_ENTRY_AREA_BASE) ||
(addr64 >= (CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE)))
return NULL;
cpu = (addr64 - CPU_ENTRY_AREA_BASE) / CPU_ENTRY_AREA_SIZE;
off = addr64 - (unsigned long)get_cpu_entry_area(cpu);
if ((off < 0) || (off >= CPU_ENTRY_AREA_SIZE))
return NULL;
metadata_array = is_origin ? cpu_entry_area_origin :
cpu_entry_area_shadow;
return &per_cpu(metadata_array[off], cpu);
}
/*
* Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
*/
static inline bool kmsan_phys_addr_valid(unsigned long addr)
{
if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
return !(addr >> boot_cpu_data.x86_phys_bits);
else
return true;
}
/*
* Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
*/
static inline bool kmsan_virt_addr_valid(void *addr)
{
unsigned long x = (unsigned long)addr;
unsigned long y = x - __START_KERNEL_map;
bool ret;
/* use the carry flag to determine if x was < __START_KERNEL_map */
if (unlikely(x > y)) {
x = y + phys_base;
if (y >= KERNEL_IMAGE_SIZE)
return false;
} else {
x = y + (__START_KERNEL_map - PAGE_OFFSET);
/* carry flag will be set if starting x was >= PAGE_OFFSET */
if ((x > y) || !kmsan_phys_addr_valid(x))
return false;
}
/*
* pfn_valid() relies on RCU, and may call into the scheduler on exiting
* the critical section. However, this would result in recursion with
* KMSAN. Therefore, disable preemption here, and re-enable preemption
* below while suppressing reschedules to avoid recursion.
*
* Note, this sacrifices occasionally breaking scheduling guarantees.
* Although, a kernel compiled with KMSAN has already given up on any
* performance guarantees due to being heavily instrumented.
*/
preempt_disable();
ret = pfn_valid(x >> PAGE_SHIFT);
preempt_enable_no_resched();
return ret;
}
#endif /* !MODULE */
#endif /* _ASM_X86_KMSAN_H */
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