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
18 DECLARE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
19 DECLARE_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 */
30 static 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 */
52 static 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 */
63 static 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 */
103
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