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| 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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