1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * x86 KMSAN support.
  4 *
  5 * Copyright (C) 2022, Google LLC
  6 * Author: Alexander Potapenko <glider@google.com>
  7 */
  8
  9#ifndef _ASM_X86_KMSAN_H
 10#define _ASM_X86_KMSAN_H
 11
 12#ifndef MODULE
 13
 14#include <asm/cpu_entry_area.h>
 15#include <asm/processor.h>
 16#include <linux/mmzone.h>
 17
 18DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
 19DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_origin);
 20
 21/*
 22 * Functions below are declared in the header to make sure they are inlined.
 23 * They all are called from kmsan_get_metadata() for every memory access in
 24 * the kernel, so speed is important here.
 25 */
 26
 27/*
 28 * Compute metadata addresses for the CPU entry area on x86.
 29 */
 30static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
 31{
 32	unsigned long addr64 = (unsigned long)addr;
 33	char *metadata_array;
 34	unsigned long off;
 35	int cpu;
 36
 37	if ((addr64 < CPU_ENTRY_AREA_BASE) ||
 38	    (addr64 >= (CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE)))
 39		return NULL;
 40	cpu = (addr64 - CPU_ENTRY_AREA_BASE) / CPU_ENTRY_AREA_SIZE;
 41	off = addr64 - (unsigned long)get_cpu_entry_area(cpu);
 42	if ((off < 0) || (off >= CPU_ENTRY_AREA_SIZE))
 43		return NULL;
 44	metadata_array = is_origin ? cpu_entry_area_origin :
 45				     cpu_entry_area_shadow;
 46	return &per_cpu(metadata_array[off], cpu);
 47}
 48
 49/*
 50 * Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
 51 */
 52static inline bool kmsan_phys_addr_valid(unsigned long addr)
 53{
 54	if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
 55		return !(addr >> boot_cpu_data.x86_phys_bits);
 56	else
 57		return true;
 58}
 59
 60/*
 61 * Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
 62 */
 63static inline bool kmsan_virt_addr_valid(void *addr)
 64{
 65	unsigned long x = (unsigned long)addr;
 66	unsigned long y = x - __START_KERNEL_map;
 67	bool ret;
 68
 69	/* use the carry flag to determine if x was < __START_KERNEL_map */
 70	if (unlikely(x > y)) {
 71		x = y + phys_base;
 72
 73		if (y >= KERNEL_IMAGE_SIZE)
 74			return false;
 75	} else {
 76		x = y + (__START_KERNEL_map - PAGE_OFFSET);
 77
 78		/* carry flag will be set if starting x was >= PAGE_OFFSET */
 79		if ((x > y) || !kmsan_phys_addr_valid(x))
 80			return false;
 81	}
 82
 83	/*
 84	 * pfn_valid() relies on RCU, and may call into the scheduler on exiting
 85	 * the critical section. However, this would result in recursion with
 86	 * KMSAN. Therefore, disable preemption here, and re-enable preemption
 87	 * below while suppressing reschedules to avoid recursion.
 88	 *
 89	 * Note, this sacrifices occasionally breaking scheduling guarantees.
 90	 * Although, a kernel compiled with KMSAN has already given up on any
 91	 * performance guarantees due to being heavily instrumented.
 92	 */
 93	preempt_disable();
 94	ret = pfn_valid(x >> PAGE_SHIFT);
 95	preempt_enable_no_resched();
 96
 97	return ret;
 98}
 99
100#endif /* !MODULE */
101
102#endif /* _ASM_X86_KMSAN_H */