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>
6 #include <xen/xen.h>
7
8 #include <asm/fpu/api.h>
9 #include <asm/fred.h>
10 #include <asm/sev.h>
11 #include <asm/traps.h>
12 #include <asm/kdebug.h>
13 #include <asm/insn-eval.h>
14 #include <asm/sgx.h>
15
16 static inline unsigned long *pt_regs_nr(struct pt_regs *regs, int nr)
17 {
18 int reg_offset = pt_regs_offset(regs, nr);
19 static unsigned long __dummy;
20
21 if (WARN_ON_ONCE(reg_offset < 0))
22 return &__dummy;
23
24 return (unsigned long *)((unsigned long)regs + reg_offset);
25 }
26
27 static inline unsigned long
28 ex_fixup_addr(const struct exception_table_entry *x)
29 {
30 return (unsigned long)&x->fixup + x->fixup;
31 }
32
33 static bool ex_handler_default(const struct exception_table_entry *e,
34 struct pt_regs *regs)
35 {
36 if (e->data & EX_FLAG_CLEAR_AX)
37 regs->ax = 0;
38 if (e->data & EX_FLAG_CLEAR_DX)
39 regs->dx = 0;
40
41 regs->ip = ex_fixup_addr(e);
42 return true;
43 }
44
45 /*
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.
48 *
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.
52 *
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.
56 */
57 static bool ex_handler_zeropad(const struct exception_table_entry *e,
58 struct pt_regs *regs,
59 unsigned long fault_addr)
60 {
61 struct insn insn;
62 const unsigned long mask = sizeof(long) - 1;
63 unsigned long offset, addr, next_ip, len;
64 unsigned long *reg;
65
66 next_ip = ex_fixup_addr(e);
67 len = next_ip - regs->ip;
68 if (len > MAX_INSN_SIZE)
69 return false;
70
71 if (insn_decode(&insn, (void *) regs->ip, len, INSN_MODE_KERN))
72 return false;
73 if (insn.length != len)
74 return false;
75
76 if (insn.opcode.bytes[0] != 0x8b)
77 return false;
78 if (insn.opnd_bytes != sizeof(long))
79 return false;
80
81 addr = (unsigned long) insn_get_addr_ref(&insn, regs);
82 if (addr == ~0ul)
83 return false;
84
85 offset = addr & mask;
86 addr = addr & ~mask;
87 if (fault_addr != addr + sizeof(long))
88 return false;
89
90 reg = insn_get_modrm_reg_ptr(&insn, regs);
91 if (!reg)
92 return false;
93
94 *reg = *(unsigned long *)addr >> (offset * 8);
95 return ex_handler_default(e, regs);
96 }
97
98 static bool ex_handler_fault(const struct exception_table_entry *fixup,
99 struct pt_regs *regs, int trapnr)
100 {
101 regs->ax = trapnr;
102 return ex_handler_default(fixup, regs);
103 }
104
105 static bool ex_handler_sgx(const struct exception_table_entry *fixup,
106 struct pt_regs *regs, int trapnr)
107 {
108 regs->ax = trapnr | SGX_ENCLS_FAULT_FLAG;
109 return ex_handler_default(fixup, regs);
110 }
111
112 /*
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.
121 */
122 static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
123 struct pt_regs *regs)
124 {
125 regs->ip = ex_fixup_addr(fixup);
126
127 WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
128 (void *)instruction_pointer(regs));
129
130 fpu_reset_from_exception_fixup();
131 return true;
132 }
133
134 /*
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.
138 *
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.
142 */
143 static bool gp_fault_address_ok(unsigned long fault_address)
144 {
145 #ifdef CONFIG_X86_64
146 /* Is it in the "user space" part of the non-canonical space? */
147 if (valid_user_address(fault_address))
148 return true;
149
150 /* .. or just above it? */
151 fault_address -= PAGE_SIZE;
152 if (valid_user_address(fault_address))
153 return true;
154 #endif
155 return false;
156 }
157
158 static bool ex_handler_uaccess(const struct exception_table_entry *fixup,
159 struct pt_regs *regs, int trapnr,
160 unsigned long fault_address)
161 {
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);
165 }
166
167 static bool ex_handler_msr(const struct exception_table_entry *fixup,
168 struct pt_regs *regs, bool wrmsr, bool safe, int reg)
169 {
170 if (__ONCE_LITE_IF(!safe && wrmsr)) {
171 pr_warn("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",
172 (unsigned int)regs->cx, (unsigned int)regs->dx,
173 (unsigned int)regs->ax, regs->ip, (void *)regs->ip);
174 show_stack_regs(regs);
175 }
176
177 if (__ONCE_LITE_IF(!safe && !wrmsr)) {
178 pr_warn("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",
179 (unsigned int)regs->cx, regs->ip, (void *)regs->ip);
180 show_stack_regs(regs);
181 }
182
183 if (!wrmsr) {
184 /* Pretend that the read succeeded and returned 0. */
185 regs->ax = 0;
186 regs->dx = 0;
187 }
188
189 if (safe)
190 *pt_regs_nr(regs, reg) = -EIO;
191
192 return ex_handler_default(fixup, regs);
193 }
194
195 static bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
196 struct pt_regs *regs)
197 {
198 if (static_cpu_has(X86_BUG_NULL_SEG))
199 asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
200 asm volatile ("mov %0, %%fs" : : "rm" (0));
201 return ex_handler_default(fixup, regs);
202 }
203
204 static bool ex_handler_imm_reg(const struct exception_table_entry *fixup,
205 struct pt_regs *regs, int reg, int imm)
206 {
207 *pt_regs_nr(regs, reg) = (long)imm;
208 return ex_handler_default(fixup, regs);
209 }
210
211 static bool ex_handler_ucopy_len(const struct exception_table_entry *fixup,
212 struct pt_regs *regs, int trapnr,
213 unsigned long fault_address,
214 int reg, int imm)
215 {
216 regs->cx = imm * regs->cx + *pt_regs_nr(regs, reg);
217 return ex_handler_uaccess(fixup, regs, trapnr, fault_address);
218 }
219
220 #ifdef CONFIG_X86_FRED
221 static bool ex_handler_eretu(const struct exception_table_entry *fixup,
222 struct pt_regs *regs, unsigned long error_code)
223 {
224 struct pt_regs *uregs = (struct pt_regs *)(regs->sp - offsetof(struct pt_regs, orig_ax));
225 unsigned short ss = uregs->ss;
226 unsigned short cs = uregs->cs;
227
228 /*
229 * Move the NMI bit from the invalid stack frame, which caused ERETU
230 * to fault, to the fault handler's stack frame, thus to unblock NMI
231 * with the fault handler's ERETS instruction ASAP if NMI is blocked.
232 */
233 regs->fred_ss.nmi = uregs->fred_ss.nmi;
234
235 /*
236 * Sync event information to uregs, i.e., the ERETU return frame, but
237 * is it safe to write to the ERETU return frame which is just above
238 * current event stack frame?
239 *
240 * The RSP used by FRED to push a stack frame is not the value in %rsp,
241 * it is calculated from %rsp with the following 2 steps:
242 * 1) RSP = %rsp - (IA32_FRED_CONFIG & 0x1c0) // Reserve N*64 bytes
243 * 2) RSP = RSP & ~0x3f // Align to a 64-byte cache line
244 * when an event delivery doesn't trigger a stack level change.
245 *
246 * Here is an example with N*64 (N=1) bytes reserved:
247 *
248 * 64-byte cache line ==> ______________
249 * |___Reserved___|
250 * |__Event_data__|
251 * |_____SS_______|
252 * |_____RSP______|
253 * |_____FLAGS____|
254 * |_____CS_______|
255 * |_____IP_______|
256 * 64-byte cache line ==> |__Error_code__| <== ERETU return frame
257 * |______________|
258 * |______________|
259 * |______________|
260 * |______________|
261 * |______________|
262 * |______________|
263 * |______________|
264 * 64-byte cache line ==> |______________| <== RSP after step 1) and 2)
265 * |___Reserved___|
266 * |__Event_data__|
267 * |_____SS_______|
268 * |_____RSP______|
269 * |_____FLAGS____|
270 * |_____CS_______|
271 * |_____IP_______|
272 * 64-byte cache line ==> |__Error_code__| <== ERETS return frame
273 *
274 * Thus a new FRED stack frame will always be pushed below a previous
275 * FRED stack frame ((N*64) bytes may be reserved between), and it is
276 * safe to write to a previous FRED stack frame as they never overlap.
277 */
278 fred_info(uregs)->edata = fred_event_data(regs);
279 uregs->ssx = regs->ssx;
280 uregs->fred_ss.ss = ss;
281 /* The NMI bit was moved away above */
282 uregs->fred_ss.nmi = 0;
283 uregs->csx = regs->csx;
284 uregs->fred_cs.sl = 0;
285 uregs->fred_cs.wfe = 0;
286 uregs->cs = cs;
287 uregs->orig_ax = error_code;
288
289 return ex_handler_default(fixup, regs);
290 }
291 #endif
292
293 int ex_get_fixup_type(unsigned long ip)
294 {
295 const struct exception_table_entry *e = search_exception_tables(ip);
296
297 return e ? FIELD_GET(EX_DATA_TYPE_MASK, e->data) : EX_TYPE_NONE;
298 }
299
300 int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
301 unsigned long fault_addr)
302 {
303 const struct exception_table_entry *e;
304 int type, reg, imm;
305
306 #ifdef CONFIG_PNPBIOS
307 if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
308 extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
309 extern u32 pnp_bios_is_utter_crap;
310 pnp_bios_is_utter_crap = 1;
311 printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
312 __asm__ volatile(
313 "movl %0, %%esp\n\t"
314 "jmp *%1\n\t"
315 : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
316 panic("do_trap: can't hit this");
317 }
318 #endif
319
320 e = search_exception_tables(regs->ip);
321 if (!e)
322 return 0;
323
324 type = FIELD_GET(EX_DATA_TYPE_MASK, e->data);
325 reg = FIELD_GET(EX_DATA_REG_MASK, e->data);
326 imm = FIELD_GET(EX_DATA_IMM_MASK, e->data);
327
328 switch (type) {
329 case EX_TYPE_DEFAULT:
330 case EX_TYPE_DEFAULT_MCE_SAFE:
331 return ex_handler_default(e, regs);
332 case EX_TYPE_FAULT:
333 case EX_TYPE_FAULT_MCE_SAFE:
334 return ex_handler_fault(e, regs, trapnr);
335 case EX_TYPE_UACCESS:
336 return ex_handler_uaccess(e, regs, trapnr, fault_addr);
337 case EX_TYPE_CLEAR_FS:
338 return ex_handler_clear_fs(e, regs);
339 case EX_TYPE_FPU_RESTORE:
340 return ex_handler_fprestore(e, regs);
341 case EX_TYPE_BPF:
342 return ex_handler_bpf(e, regs);
343 case EX_TYPE_WRMSR:
344 return ex_handler_msr(e, regs, true, false, reg);
345 case EX_TYPE_RDMSR:
346 return ex_handler_msr(e, regs, false, false, reg);
347 case EX_TYPE_WRMSR_SAFE:
348 return ex_handler_msr(e, regs, true, true, reg);
349 case EX_TYPE_RDMSR_SAFE:
350 return ex_handler_msr(e, regs, false, true, reg);
351 case EX_TYPE_WRMSR_IN_MCE:
352 ex_handler_msr_mce(regs, true);
353 break;
354 case EX_TYPE_RDMSR_IN_MCE:
355 ex_handler_msr_mce(regs, false);
356 break;
357 case EX_TYPE_POP_REG:
358 regs->sp += sizeof(long);
359 fallthrough;
360 case EX_TYPE_IMM_REG:
361 return ex_handler_imm_reg(e, regs, reg, imm);
362 case EX_TYPE_FAULT_SGX:
363 return ex_handler_sgx(e, regs, trapnr);
364 case EX_TYPE_UCOPY_LEN:
365 return ex_handler_ucopy_len(e, regs, trapnr, fault_addr, reg, imm);
366 case EX_TYPE_ZEROPAD:
367 return ex_handler_zeropad(e, regs, fault_addr);
368 #ifdef CONFIG_X86_FRED
369 case EX_TYPE_ERETU:
370 return ex_handler_eretu(e, regs, error_code);
371 #endif
372 }
373 BUG();
374 }
375
376 extern unsigned int early_recursion_flag;
377
378 /* Restricted version used during very early boot */
379 void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
380 {
381 /* Ignore early NMIs. */
382 if (trapnr == X86_TRAP_NMI)
383 return;
384
385 if (early_recursion_flag > 2)
386 goto halt_loop;
387
388 /*
389 * Old CPUs leave the high bits of CS on the stack
390 * undefined. I'm not sure which CPUs do this, but at least
391 * the 486 DX works this way.
392 * Xen pv domains are not using the default __KERNEL_CS.
393 */
394 if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
395 goto fail;
396
397 /*
398 * The full exception fixup machinery is available as soon as
399 * the early IDT is loaded. This means that it is the
400 * responsibility of extable users to either function correctly
401 * when handlers are invoked early or to simply avoid causing
402 * exceptions before they're ready to handle them.
403 *
404 * This is better than filtering which handlers can be used,
405 * because refusing to call a handler here is guaranteed to
406 * result in a hard-to-debug panic.
407 *
408 * Keep in mind that not all vectors actually get here. Early
409 * page faults, for example, are special.
410 */
411 if (fixup_exception(regs, trapnr, regs->orig_ax, 0))
412 return;
413
414 if (trapnr == X86_TRAP_UD) {
415 if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
416 /* Skip the ud2. */
417 regs->ip += LEN_UD2;
418 return;
419 }
420
421 /*
422 * If this was a BUG and report_bug returns or if this
423 * was just a normal #UD, we want to continue onward and
424 * crash.
425 */
426 }
427
428 fail:
429 early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
430 (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
431 regs->orig_ax, read_cr2());
432
433 show_regs(regs);
434
435 halt_loop:
436 while (true)
437 halt();
438 }
439
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