1 // SPDX-License-Identifier: GPL-2.0-only 2 #include <linux/extable.h> 3 #include <linux/uaccess.h> 4 #include <linux/sched/debug.h> 5 #include <xen/xen.h> 6 7 #include <asm/fpu/api.h> 8 #include <asm/sev.h> 9 #include <asm/traps.h> 10 #include <asm/kdebug.h> 11 12 static inline unsigned long 13 ex_fixup_addr(const struct exception_table_entry *x) 14 { 15 return (unsigned long)&x->fixup + x->fixup; 16 } 17 18 static bool ex_handler_default(const struct exception_table_entry *fixup, 19 struct pt_regs *regs) 20 { 21 regs->ip = ex_fixup_addr(fixup); 22 return true; 23 } 24 25 static bool ex_handler_fault(const struct exception_table_entry *fixup, 26 struct pt_regs *regs, int trapnr) 27 { 28 regs->ax = trapnr; 29 return ex_handler_default(fixup, regs); 30 } 31 32 /* 33 * Handler for when we fail to restore a task's FPU state. We should never get 34 * here because the FPU state of a task using the FPU (task->thread.fpu.state) 35 * should always be valid. However, past bugs have allowed userspace to set 36 * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn(). 37 * These caused XRSTOR to fail when switching to the task, leaking the FPU 38 * registers of the task previously executing on the CPU. Mitigate this class 39 * of vulnerability by restoring from the initial state (essentially, zeroing 40 * out all the FPU registers) if we can't restore from the task's FPU state. 41 */ 42 static bool ex_handler_fprestore(const struct exception_table_entry *fixup, 43 struct pt_regs *regs) 44 { 45 regs->ip = ex_fixup_addr(fixup); 46 47 WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.", 48 (void *)instruction_pointer(regs)); 49 50 fpu_reset_from_exception_fixup(); 51 return true; 52 } 53 54 static bool ex_handler_uaccess(const struct exception_table_entry *fixup, 55 struct pt_regs *regs, int trapnr) 56 { 57 WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?"); 58 return ex_handler_default(fixup, regs); 59 } 60 61 static bool ex_handler_copy(const struct exception_table_entry *fixup, 62 struct pt_regs *regs, int trapnr) 63 { 64 WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?"); 65 return ex_handler_fault(fixup, regs, trapnr); 66 } 67 68 static bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, 69 struct pt_regs *regs) 70 { 71 if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n", 72 (unsigned int)regs->cx, regs->ip, (void *)regs->ip)) 73 show_stack_regs(regs); 74 75 /* Pretend that the read succeeded and returned 0. */ 76 regs->ax = 0; 77 regs->dx = 0; 78 return ex_handler_default(fixup, regs); 79 } 80 81 static bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup, 82 struct pt_regs *regs) 83 { 84 if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n", 85 (unsigned int)regs->cx, (unsigned int)regs->dx, 86 (unsigned int)regs->ax, regs->ip, (void *)regs->ip)) 87 show_stack_regs(regs); 88 89 /* Pretend that the write succeeded. */ 90 return ex_handler_default(fixup, regs); 91 } 92 93 static bool ex_handler_clear_fs(const struct exception_table_entry *fixup, 94 struct pt_regs *regs) 95 { 96 if (static_cpu_has(X86_BUG_NULL_SEG)) 97 asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS)); 98 asm volatile ("mov %0, %%fs" : : "rm" (0)); 99 return ex_handler_default(fixup, regs); 100 } 101 102 int ex_get_fixup_type(unsigned long ip) 103 { 104 const struct exception_table_entry *e = search_exception_tables(ip); 105 106 return e ? e->type : EX_TYPE_NONE; 107 } 108 109 int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code, 110 unsigned long fault_addr) 111 { 112 const struct exception_table_entry *e; 113 114 #ifdef CONFIG_PNPBIOS 115 if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) { 116 extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp; 117 extern u32 pnp_bios_is_utter_crap; 118 pnp_bios_is_utter_crap = 1; 119 printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n"); 120 __asm__ volatile( 121 "movl %0, %%esp\n\t" 122 "jmp *%1\n\t" 123 : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip)); 124 panic("do_trap: can't hit this"); 125 } 126 #endif 127 128 e = search_exception_tables(regs->ip); 129 if (!e) 130 return 0; 131 132 switch (e->type) { 133 case EX_TYPE_DEFAULT: 134 case EX_TYPE_DEFAULT_MCE_SAFE: 135 return ex_handler_default(e, regs); 136 case EX_TYPE_FAULT: 137 case EX_TYPE_FAULT_MCE_SAFE: 138 return ex_handler_fault(e, regs, trapnr); 139 case EX_TYPE_UACCESS: 140 return ex_handler_uaccess(e, regs, trapnr); 141 case EX_TYPE_COPY: 142 return ex_handler_copy(e, regs, trapnr); 143 case EX_TYPE_CLEAR_FS: 144 return ex_handler_clear_fs(e, regs); 145 case EX_TYPE_FPU_RESTORE: 146 return ex_handler_fprestore(e, regs); 147 case EX_TYPE_RDMSR: 148 return ex_handler_rdmsr_unsafe(e, regs); 149 case EX_TYPE_WRMSR: 150 return ex_handler_wrmsr_unsafe(e, regs); 151 case EX_TYPE_BPF: 152 return ex_handler_bpf(e, regs); 153 case EX_TYPE_RDMSR_IN_MCE: 154 ex_handler_msr_mce(regs, false); 155 break; 156 case EX_TYPE_WRMSR_IN_MCE: 157 ex_handler_msr_mce(regs, true); 158 break; 159 } 160 BUG(); 161 } 162 163 extern unsigned int early_recursion_flag; 164 165 /* Restricted version used during very early boot */ 166 void __init early_fixup_exception(struct pt_regs *regs, int trapnr) 167 { 168 /* Ignore early NMIs. */ 169 if (trapnr == X86_TRAP_NMI) 170 return; 171 172 if (early_recursion_flag > 2) 173 goto halt_loop; 174 175 /* 176 * Old CPUs leave the high bits of CS on the stack 177 * undefined. I'm not sure which CPUs do this, but at least 178 * the 486 DX works this way. 179 * Xen pv domains are not using the default __KERNEL_CS. 180 */ 181 if (!xen_pv_domain() && regs->cs != __KERNEL_CS) 182 goto fail; 183 184 /* 185 * The full exception fixup machinery is available as soon as 186 * the early IDT is loaded. This means that it is the 187 * responsibility of extable users to either function correctly 188 * when handlers are invoked early or to simply avoid causing 189 * exceptions before they're ready to handle them. 190 * 191 * This is better than filtering which handlers can be used, 192 * because refusing to call a handler here is guaranteed to 193 * result in a hard-to-debug panic. 194 * 195 * Keep in mind that not all vectors actually get here. Early 196 * page faults, for example, are special. 197 */ 198 if (fixup_exception(regs, trapnr, regs->orig_ax, 0)) 199 return; 200 201 if (trapnr == X86_TRAP_UD) { 202 if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) { 203 /* Skip the ud2. */ 204 regs->ip += LEN_UD2; 205 return; 206 } 207 208 /* 209 * If this was a BUG and report_bug returns or if this 210 * was just a normal #UD, we want to continue onward and 211 * crash. 212 */ 213 } 214 215 fail: 216 early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n", 217 (unsigned)trapnr, (unsigned long)regs->cs, regs->ip, 218 regs->orig_ax, read_cr2()); 219 220 show_regs(regs); 221 222 halt_loop: 223 while (true) 224 halt(); 225 } 226