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 <linux/bitfield.h>
8 #include <asm/fpu/api.h>
11 #include <asm/traps.h>
12 #include <asm/kdebug.h>
13 #include <asm/insn-eval.h>
16 static inline unsigned long *pt_regs_nr(struct pt_regs *regs, int nr)
18 int reg_offset = pt_regs_offset(regs, nr);
19 static unsigned long __dummy;
21 if (WARN_ON_ONCE(reg_offset < 0))
24 return (unsigned long *)((unsigned long)regs + reg_offset);
27 static inline unsigned long
28 ex_fixup_addr(const struct exception_table_entry *x)
30 return (unsigned long)&x->fixup + x->fixup;
33 static bool ex_handler_default(const struct exception_table_entry *e,
36 if (e->data & EX_FLAG_CLEAR_AX)
38 if (e->data & EX_FLAG_CLEAR_DX)
41 regs->ip = ex_fixup_addr(e);
46 * This is the *very* rare case where we do a "load_unaligned_zeropad()"
47 * and it's a page crosser into a non-existent page.
49 * This happens when we optimistically load a pathname a word-at-a-time
50 * and the name is less than the full word and the next page is not
51 * mapped. Typically that only happens for CONFIG_DEBUG_PAGEALLOC.
53 * NOTE! The faulting address is always a 'mov mem,reg' type instruction
54 * of size 'long', and the exception fixup must always point to right
55 * after the instruction.
57 static bool ex_handler_zeropad(const struct exception_table_entry *e,
59 unsigned long fault_addr)
62 const unsigned long mask = sizeof(long) - 1;
63 unsigned long offset, addr, next_ip, len;
66 next_ip = ex_fixup_addr(e);
67 len = next_ip - regs->ip;
68 if (len > MAX_INSN_SIZE)
71 if (insn_decode(&insn, (void *) regs->ip, len, INSN_MODE_KERN))
73 if (insn.length != len)
76 if (insn.opcode.bytes[0] != 0x8b)
78 if (insn.opnd_bytes != sizeof(long))
81 addr = (unsigned long) insn_get_addr_ref(&insn, regs);
87 if (fault_addr != addr + sizeof(long))
90 reg = insn_get_modrm_reg_ptr(&insn, regs);
94 *reg = *(unsigned long *)addr >> (offset * 8);
95 return ex_handler_default(e, regs);
98 static bool ex_handler_fault(const struct exception_table_entry *fixup,
99 struct pt_regs *regs, int trapnr)
102 return ex_handler_default(fixup, regs);
105 static bool ex_handler_sgx(const struct exception_table_entry *fixup,
106 struct pt_regs *regs, int trapnr)
108 regs->ax = trapnr | SGX_ENCLS_FAULT_FLAG;
109 return ex_handler_default(fixup, regs);
113 * Handler for when we fail to restore a task's FPU state. We should never get
114 * here because the FPU state of a task using the FPU (task->thread.fpu.state)
115 * should always be valid. However, past bugs have allowed userspace to set
116 * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
117 * These caused XRSTOR to fail when switching to the task, leaking the FPU
118 * registers of the task previously executing on the CPU. Mitigate this class
119 * of vulnerability by restoring from the initial state (essentially, zeroing
120 * out all the FPU registers) if we can't restore from the task's FPU state.
122 static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
123 struct pt_regs *regs)
125 regs->ip = ex_fixup_addr(fixup);
127 WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
128 (void *)instruction_pointer(regs));
130 fpu_reset_from_exception_fixup();
135 * On x86-64, we end up being imprecise with 'access_ok()', and allow
136 * non-canonical user addresses to make the range comparisons simpler,
137 * and to not have to worry about LAM being enabled.
139 * In fact, we allow up to one page of "slop" at the sign boundary,
140 * which means that we can do access_ok() by just checking the sign
141 * of the pointer for the common case of having a small access size.
143 static bool gp_fault_address_ok(unsigned long fault_address)
146 /* Is it in the "user space" part of the non-canonical space? */
147 if (valid_user_address(fault_address))
150 /* .. or just above it? */
151 fault_address -= PAGE_SIZE;
152 if (valid_user_address(fault_address))
158 static bool ex_handler_uaccess(const struct exception_table_entry *fixup,
159 struct pt_regs *regs, int trapnr,
160 unsigned long fault_address)
162 WARN_ONCE(trapnr == X86_TRAP_GP && !gp_fault_address_ok(fault_address),
163 "General protection fault in user access. Non-canonical address?");
164 return ex_handler_default(fixup, regs);
167 static bool ex_handler_copy(const struct exception_table_entry *fixup,
168 struct pt_regs *regs, int trapnr)
170 WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?");
171 return ex_handler_fault(fixup, regs, trapnr);
174 static bool ex_handler_msr(const struct exception_table_entry *fixup,
175 struct pt_regs *regs, bool wrmsr, bool safe, int reg)
177 if (__ONCE_LITE_IF(!safe && wrmsr)) {
178 pr_warn("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",
179 (unsigned int)regs->cx, (unsigned int)regs->dx,
180 (unsigned int)regs->ax, regs->ip, (void *)regs->ip);
181 show_stack_regs(regs);
184 if (__ONCE_LITE_IF(!safe && !wrmsr)) {
185 pr_warn("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",
186 (unsigned int)regs->cx, regs->ip, (void *)regs->ip);
187 show_stack_regs(regs);
191 /* Pretend that the read succeeded and returned 0. */
197 *pt_regs_nr(regs, reg) = -EIO;
199 return ex_handler_default(fixup, regs);
202 static bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
203 struct pt_regs *regs)
205 if (static_cpu_has(X86_BUG_NULL_SEG))
206 asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
207 asm volatile ("mov %0, %%fs" : : "rm" (0));
208 return ex_handler_default(fixup, regs);
211 static bool ex_handler_imm_reg(const struct exception_table_entry *fixup,
212 struct pt_regs *regs, int reg, int imm)
214 *pt_regs_nr(regs, reg) = (long)imm;
215 return ex_handler_default(fixup, regs);
218 static bool ex_handler_ucopy_len(const struct exception_table_entry *fixup,
219 struct pt_regs *regs, int trapnr,
220 unsigned long fault_address,
223 regs->cx = imm * regs->cx + *pt_regs_nr(regs, reg);
224 return ex_handler_uaccess(fixup, regs, trapnr, fault_address);
227 #ifdef CONFIG_X86_FRED
228 static bool ex_handler_eretu(const struct exception_table_entry *fixup,
229 struct pt_regs *regs, unsigned long error_code)
231 struct pt_regs *uregs = (struct pt_regs *)(regs->sp - offsetof(struct pt_regs, orig_ax));
232 unsigned short ss = uregs->ss;
233 unsigned short cs = uregs->cs;
236 * Move the NMI bit from the invalid stack frame, which caused ERETU
237 * to fault, to the fault handler's stack frame, thus to unblock NMI
238 * with the fault handler's ERETS instruction ASAP if NMI is blocked.
240 regs->fred_ss.nmi = uregs->fred_ss.nmi;
243 * Sync event information to uregs, i.e., the ERETU return frame, but
244 * is it safe to write to the ERETU return frame which is just above
245 * current event stack frame?
247 * The RSP used by FRED to push a stack frame is not the value in %rsp,
248 * it is calculated from %rsp with the following 2 steps:
249 * 1) RSP = %rsp - (IA32_FRED_CONFIG & 0x1c0) // Reserve N*64 bytes
250 * 2) RSP = RSP & ~0x3f // Align to a 64-byte cache line
251 * when an event delivery doesn't trigger a stack level change.
253 * Here is an example with N*64 (N=1) bytes reserved:
255 * 64-byte cache line ==> ______________
263 * 64-byte cache line ==> |__Error_code__| <== ERETU return frame
271 * 64-byte cache line ==> |______________| <== RSP after step 1) and 2)
279 * 64-byte cache line ==> |__Error_code__| <== ERETS return frame
281 * Thus a new FRED stack frame will always be pushed below a previous
282 * FRED stack frame ((N*64) bytes may be reserved between), and it is
283 * safe to write to a previous FRED stack frame as they never overlap.
285 fred_info(uregs)->edata = fred_event_data(regs);
286 uregs->ssx = regs->ssx;
287 uregs->fred_ss.ss = ss;
288 /* The NMI bit was moved away above */
289 uregs->fred_ss.nmi = 0;
290 uregs->csx = regs->csx;
291 uregs->fred_cs.sl = 0;
292 uregs->fred_cs.wfe = 0;
294 uregs->orig_ax = error_code;
296 return ex_handler_default(fixup, regs);
300 int ex_get_fixup_type(unsigned long ip)
302 const struct exception_table_entry *e = search_exception_tables(ip);
304 return e ? FIELD_GET(EX_DATA_TYPE_MASK, e->data) : EX_TYPE_NONE;
307 int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
308 unsigned long fault_addr)
310 const struct exception_table_entry *e;
313 #ifdef CONFIG_PNPBIOS
314 if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
315 extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
316 extern u32 pnp_bios_is_utter_crap;
317 pnp_bios_is_utter_crap = 1;
318 printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
322 : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
323 panic("do_trap: can't hit this");
327 e = search_exception_tables(regs->ip);
331 type = FIELD_GET(EX_DATA_TYPE_MASK, e->data);
332 reg = FIELD_GET(EX_DATA_REG_MASK, e->data);
333 imm = FIELD_GET(EX_DATA_IMM_MASK, e->data);
336 case EX_TYPE_DEFAULT:
337 case EX_TYPE_DEFAULT_MCE_SAFE:
338 return ex_handler_default(e, regs);
340 case EX_TYPE_FAULT_MCE_SAFE:
341 return ex_handler_fault(e, regs, trapnr);
342 case EX_TYPE_UACCESS:
343 return ex_handler_uaccess(e, regs, trapnr, fault_addr);
345 return ex_handler_copy(e, regs, trapnr);
346 case EX_TYPE_CLEAR_FS:
347 return ex_handler_clear_fs(e, regs);
348 case EX_TYPE_FPU_RESTORE:
349 return ex_handler_fprestore(e, regs);
351 return ex_handler_bpf(e, regs);
353 return ex_handler_msr(e, regs, true, false, reg);
355 return ex_handler_msr(e, regs, false, false, reg);
356 case EX_TYPE_WRMSR_SAFE:
357 return ex_handler_msr(e, regs, true, true, reg);
358 case EX_TYPE_RDMSR_SAFE:
359 return ex_handler_msr(e, regs, false, true, reg);
360 case EX_TYPE_WRMSR_IN_MCE:
361 ex_handler_msr_mce(regs, true);
363 case EX_TYPE_RDMSR_IN_MCE:
364 ex_handler_msr_mce(regs, false);
366 case EX_TYPE_POP_REG:
367 regs->sp += sizeof(long);
369 case EX_TYPE_IMM_REG:
370 return ex_handler_imm_reg(e, regs, reg, imm);
371 case EX_TYPE_FAULT_SGX:
372 return ex_handler_sgx(e, regs, trapnr);
373 case EX_TYPE_UCOPY_LEN:
374 return ex_handler_ucopy_len(e, regs, trapnr, fault_addr, reg, imm);
375 case EX_TYPE_ZEROPAD:
376 return ex_handler_zeropad(e, regs, fault_addr);
377 #ifdef CONFIG_X86_FRED
379 return ex_handler_eretu(e, regs, error_code);
385 extern unsigned int early_recursion_flag;
387 /* Restricted version used during very early boot */
388 void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
390 /* Ignore early NMIs. */
391 if (trapnr == X86_TRAP_NMI)
394 if (early_recursion_flag > 2)
398 * Old CPUs leave the high bits of CS on the stack
399 * undefined. I'm not sure which CPUs do this, but at least
400 * the 486 DX works this way.
401 * Xen pv domains are not using the default __KERNEL_CS.
403 if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
407 * The full exception fixup machinery is available as soon as
408 * the early IDT is loaded. This means that it is the
409 * responsibility of extable users to either function correctly
410 * when handlers are invoked early or to simply avoid causing
411 * exceptions before they're ready to handle them.
413 * This is better than filtering which handlers can be used,
414 * because refusing to call a handler here is guaranteed to
415 * result in a hard-to-debug panic.
417 * Keep in mind that not all vectors actually get here. Early
418 * page faults, for example, are special.
420 if (fixup_exception(regs, trapnr, regs->orig_ax, 0))
423 if (trapnr == X86_TRAP_UD) {
424 if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
431 * If this was a BUG and report_bug returns or if this
432 * was just a normal #UD, we want to continue onward and
438 early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
439 (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
440 regs->orig_ax, read_cr2());