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