1 /* SPDX-License-Identifier: GPL-2.0 */
2 #include <linux/jump_label.h>
3 #include <asm/unwind_hints.h>
4 #include <asm/cpufeatures.h>
5 #include <asm/page_types.h>
6 #include <asm/percpu.h>
7 #include <asm/asm-offsets.h>
8 #include <asm/processor-flags.h>
9 #include <asm/ptrace-abi.h>
10 #include <asm/msr.h>
11 #include <asm/nospec-branch.h>
12
13 /*
14
15 x86 function call convention, 64-bit:
16 -------------------------------------
17 arguments | callee-saved | extra caller-saved | return
18 [callee-clobbered] | | [callee-clobbered] |
19 ---------------------------------------------------------------------------
20 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**]
21
22 ( rsp is obviously invariant across normal function calls. (gcc can 'merge'
23 functions when it sees tail-call optimization possibilities) rflags is
24 clobbered. Leftover arguments are passed over the stack frame.)
25
26 [*] In the frame-pointers case rbp is fixed to the stack frame.
27
28 [**] for struct return values wider than 64 bits the return convention is a
29 bit more complex: up to 128 bits width we return small structures
30 straight in rax, rdx. For structures larger than that (3 words or
31 larger) the caller puts a pointer to an on-stack return struct
32 [allocated in the caller's stack frame] into the first argument - i.e.
33 into rdi. All other arguments shift up by one in this case.
34 Fortunately this case is rare in the kernel.
35
36 For 32-bit we have the following conventions - kernel is built with
37 -mregparm=3 and -freg-struct-return:
38
39 x86 function calling convention, 32-bit:
40 ----------------------------------------
41 arguments | callee-saved | extra caller-saved | return
42 [callee-clobbered] | | [callee-clobbered] |
43 -------------------------------------------------------------------------
44 eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**]
45
46 ( here too esp is obviously invariant across normal function calls. eflags
47 is clobbered. Leftover arguments are passed over the stack frame. )
48
49 [*] In the frame-pointers case ebp is fixed to the stack frame.
50
51 [**] We build with -freg-struct-return, which on 32-bit means similar
52 semantics as on 64-bit: edx can be used for a second return value
53 (i.e. covering integer and structure sizes up to 64 bits) - after that
54 it gets more complex and more expensive: 3-word or larger struct returns
55 get done in the caller's frame and the pointer to the return struct goes
56 into regparm0, i.e. eax - the other arguments shift up and the
57 function's register parameters degenerate to regparm=2 in essence.
58
59 */
60
61 #ifdef CONFIG_X86_64
62
63 /*
64 * 64-bit system call stack frame layout defines and helpers,
65 * for assembly code:
66 */
67
68 .macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 unwind_hint=1
69 .if \save_ret
70 pushq %rsi /* pt_regs->si */
71 movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */
72 movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */
73 .else
74 pushq %rdi /* pt_regs->di */
75 pushq %rsi /* pt_regs->si */
76 .endif
77 pushq \rdx /* pt_regs->dx */
78 pushq \rcx /* pt_regs->cx */
79 pushq \rax /* pt_regs->ax */
80 pushq %r8 /* pt_regs->r8 */
81 pushq %r9 /* pt_regs->r9 */
82 pushq %r10 /* pt_regs->r10 */
83 pushq %r11 /* pt_regs->r11 */
84 pushq %rbx /* pt_regs->rbx */
85 pushq %rbp /* pt_regs->rbp */
86 pushq %r12 /* pt_regs->r12 */
87 pushq %r13 /* pt_regs->r13 */
88 pushq %r14 /* pt_regs->r14 */
89 pushq %r15 /* pt_regs->r15 */
90
91 .if \unwind_hint
92 UNWIND_HINT_REGS
93 .endif
94
95 .if \save_ret
96 pushq %rsi /* return address on top of stack */
97 .endif
98 .endm
99
100 .macro CLEAR_REGS clear_bp=1
101 /*
102 * Sanitize registers of values that a speculation attack might
103 * otherwise want to exploit. The lower registers are likely clobbered
104 * well before they could be put to use in a speculative execution
105 * gadget.
106 */
107 xorl %esi, %esi /* nospec si */
108 xorl %edx, %edx /* nospec dx */
109 xorl %ecx, %ecx /* nospec cx */
110 xorl %r8d, %r8d /* nospec r8 */
111 xorl %r9d, %r9d /* nospec r9 */
112 xorl %r10d, %r10d /* nospec r10 */
113 xorl %r11d, %r11d /* nospec r11 */
114 xorl %ebx, %ebx /* nospec rbx */
115 .if \clear_bp
116 xorl %ebp, %ebp /* nospec rbp */
117 .endif
118 xorl %r12d, %r12d /* nospec r12 */
119 xorl %r13d, %r13d /* nospec r13 */
120 xorl %r14d, %r14d /* nospec r14 */
121 xorl %r15d, %r15d /* nospec r15 */
122
123 .endm
124
125 .macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 clear_bp=1 unwind_hint=1
126 PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret unwind_hint=\unwind_hint
127 CLEAR_REGS clear_bp=\clear_bp
128 .endm
129
130 .macro POP_REGS pop_rdi=1
131 popq %r15
132 popq %r14
133 popq %r13
134 popq %r12
135 popq %rbp
136 popq %rbx
137 popq %r11
138 popq %r10
139 popq %r9
140 popq %r8
141 popq %rax
142 popq %rcx
143 popq %rdx
144 popq %rsi
145 .if \pop_rdi
146 popq %rdi
147 .endif
148 .endm
149
150 #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION
151
152 /*
153 * MITIGATION_PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two
154 * halves:
155 */
156 #define PTI_USER_PGTABLE_BIT PAGE_SHIFT
157 #define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT)
158 #define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT
159 #define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT)
160 #define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK)
161
162 .macro SET_NOFLUSH_BIT reg:req
163 bts $X86_CR3_PCID_NOFLUSH_BIT, \reg
164 .endm
165
166 .macro ADJUST_KERNEL_CR3 reg:req
167 ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID
168 /* Clear PCID and "MITIGATION_PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */
169 andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg
170 .endm
171
172 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
173 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
174 mov %cr3, \scratch_reg
175 ADJUST_KERNEL_CR3 \scratch_reg
176 mov \scratch_reg, %cr3
177 .Lend_\@:
178 .endm
179
180 #define THIS_CPU_user_pcid_flush_mask \
181 PER_CPU_VAR(cpu_tlbstate + TLB_STATE_user_pcid_flush_mask)
182
183 .macro SWITCH_TO_USER_CR3 scratch_reg:req scratch_reg2:req
184 mov %cr3, \scratch_reg
185
186 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
187
188 /*
189 * Test if the ASID needs a flush.
190 */
191 movq \scratch_reg, \scratch_reg2
192 andq $(0x7FF), \scratch_reg /* mask ASID */
193 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
194 jnc .Lnoflush_\@
195
196 /* Flush needed, clear the bit */
197 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
198 movq \scratch_reg2, \scratch_reg
199 jmp .Lwrcr3_pcid_\@
200
201 .Lnoflush_\@:
202 movq \scratch_reg2, \scratch_reg
203 SET_NOFLUSH_BIT \scratch_reg
204
205 .Lwrcr3_pcid_\@:
206 /* Flip the ASID to the user version */
207 orq $(PTI_USER_PCID_MASK), \scratch_reg
208
209 .Lwrcr3_\@:
210 /* Flip the PGD to the user version */
211 orq $(PTI_USER_PGTABLE_MASK), \scratch_reg
212 mov \scratch_reg, %cr3
213 .endm
214
215 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
216 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
217 SWITCH_TO_USER_CR3 \scratch_reg \scratch_reg2
218 .Lend_\@:
219 .endm
220
221 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
222 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
223 pushq %rax
224 SWITCH_TO_USER_CR3 scratch_reg=\scratch_reg scratch_reg2=%rax
225 popq %rax
226 .Lend_\@:
227 .endm
228
229 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
230 ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI
231 movq %cr3, \scratch_reg
232 movq \scratch_reg, \save_reg
233 /*
234 * Test the user pagetable bit. If set, then the user page tables
235 * are active. If clear CR3 already has the kernel page table
236 * active.
237 */
238 bt $PTI_USER_PGTABLE_BIT, \scratch_reg
239 jnc .Ldone_\@
240
241 ADJUST_KERNEL_CR3 \scratch_reg
242 movq \scratch_reg, %cr3
243
244 .Ldone_\@:
245 .endm
246
247 /* Restore CR3 from a kernel context. May restore a user CR3 value. */
248 .macro PARANOID_RESTORE_CR3 scratch_reg:req save_reg:req
249 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
250
251 /*
252 * If CR3 contained the kernel page tables at the paranoid exception
253 * entry, then there is nothing to restore as CR3 is not modified while
254 * handling the exception.
255 */
256 bt $PTI_USER_PGTABLE_BIT, \save_reg
257 jnc .Lend_\@
258
259 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
260
261 /*
262 * Check if there's a pending flush for the user ASID we're
263 * about to set.
264 */
265 movq \save_reg, \scratch_reg
266 andq $(0x7FF), \scratch_reg
267 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
268 jc .Lwrcr3_\@
269
270 SET_NOFLUSH_BIT \save_reg
271
272 .Lwrcr3_\@:
273 movq \save_reg, %cr3
274 .Lend_\@:
275 .endm
276
277 #else /* CONFIG_MITIGATION_PAGE_TABLE_ISOLATION=n: */
278
279 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
280 .endm
281 .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
282 .endm
283 .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
284 .endm
285 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
286 .endm
287 .macro PARANOID_RESTORE_CR3 scratch_reg:req save_reg:req
288 .endm
289
290 #endif
291
292 /*
293 * IBRS kernel mitigation for Spectre_v2.
294 *
295 * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
296 * the regs it uses (AX, CX, DX). Must be called before the first RET
297 * instruction (NOTE! UNTRAIN_RET includes a RET instruction)
298 *
299 * The optional argument is used to save/restore the current value,
300 * which is used on the paranoid paths.
301 *
302 * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
303 */
304 .macro IBRS_ENTER save_reg
305 #ifdef CONFIG_MITIGATION_IBRS_ENTRY
306 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
307 movl $MSR_IA32_SPEC_CTRL, %ecx
308
309 .ifnb \save_reg
310 rdmsr
311 shl $32, %rdx
312 or %rdx, %rax
313 mov %rax, \save_reg
314 test $SPEC_CTRL_IBRS, %eax
315 jz .Ldo_wrmsr_\@
316 lfence
317 jmp .Lend_\@
318 .Ldo_wrmsr_\@:
319 .endif
320
321 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
322 movl %edx, %eax
323 shr $32, %rdx
324 wrmsr
325 .Lend_\@:
326 #endif
327 .endm
328
329 /*
330 * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
331 * regs. Must be called after the last RET.
332 */
333 .macro IBRS_EXIT save_reg
334 #ifdef CONFIG_MITIGATION_IBRS_ENTRY
335 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
336 movl $MSR_IA32_SPEC_CTRL, %ecx
337
338 .ifnb \save_reg
339 mov \save_reg, %rdx
340 .else
341 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
342 andl $(~SPEC_CTRL_IBRS), %edx
343 .endif
344
345 movl %edx, %eax
346 shr $32, %rdx
347 wrmsr
348 .Lend_\@:
349 #endif
350 .endm
351
352 /*
353 * Mitigate Spectre v1 for conditional swapgs code paths.
354 *
355 * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to
356 * prevent a speculative swapgs when coming from kernel space.
357 *
358 * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path,
359 * to prevent the swapgs from getting speculatively skipped when coming from
360 * user space.
361 */
362 .macro FENCE_SWAPGS_USER_ENTRY
363 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER
364 .endm
365 .macro FENCE_SWAPGS_KERNEL_ENTRY
366 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL
367 .endm
368
369 .macro STACKLEAK_ERASE_NOCLOBBER
370 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
371 PUSH_AND_CLEAR_REGS
372 call stackleak_erase
373 POP_REGS
374 #endif
375 .endm
376
377 .macro SAVE_AND_SET_GSBASE scratch_reg:req save_reg:req
378 rdgsbase \save_reg
379 GET_PERCPU_BASE \scratch_reg
380 wrgsbase \scratch_reg
381 .endm
382
383 #else /* CONFIG_X86_64 */
384 # undef UNWIND_HINT_IRET_REGS
385 # define UNWIND_HINT_IRET_REGS
386 #endif /* !CONFIG_X86_64 */
387
388 .macro STACKLEAK_ERASE
389 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
390 call stackleak_erase
391 #endif
392 .endm
393
394 #ifdef CONFIG_SMP
395
396 /*
397 * CPU/node NR is loaded from the limit (size) field of a special segment
398 * descriptor entry in GDT.
399 */
400 .macro LOAD_CPU_AND_NODE_SEG_LIMIT reg:req
401 movq $__CPUNODE_SEG, \reg
402 lsl \reg, \reg
403 .endm
404
405 /*
406 * Fetch the per-CPU GSBASE value for this processor and put it in @reg.
407 * We normally use %gs for accessing per-CPU data, but we are setting up
408 * %gs here and obviously can not use %gs itself to access per-CPU data.
409 *
410 * Do not use RDPID, because KVM loads guest's TSC_AUX on vm-entry and
411 * may not restore the host's value until the CPU returns to userspace.
412 * Thus the kernel would consume a guest's TSC_AUX if an NMI arrives
413 * while running KVM's run loop.
414 */
415 .macro GET_PERCPU_BASE reg:req
416 LOAD_CPU_AND_NODE_SEG_LIMIT \reg
417 andq $VDSO_CPUNODE_MASK, \reg
418 movq __per_cpu_offset(, \reg, 8), \reg
419 .endm
420
421 #else
422
423 .macro GET_PERCPU_BASE reg:req
424 movq pcpu_unit_offsets(%rip), \reg
425 .endm
426
427 #endif /* CONFIG_SMP */
428
429 #ifdef CONFIG_X86_64
430
431 /* rdi: arg1 ... normal C conventions. rax is saved/restored. */
432 .macro THUNK name, func
433 SYM_FUNC_START(\name)
434 pushq %rbp
435 movq %rsp, %rbp
436
437 pushq %rdi
438 pushq %rsi
439 pushq %rdx
440 pushq %rcx
441 pushq %rax
442 pushq %r8
443 pushq %r9
444 pushq %r10
445 pushq %r11
446
447 call \func
448
449 popq %r11
450 popq %r10
451 popq %r9
452 popq %r8
453 popq %rax
454 popq %rcx
455 popq %rdx
456 popq %rsi
457 popq %rdi
458 popq %rbp
459 RET
460 SYM_FUNC_END(\name)
461 _ASM_NOKPROBE(\name)
462 .endm
463
464 #else /* CONFIG_X86_32 */
465
466 /* put return address in eax (arg1) */
467 .macro THUNK name, func, put_ret_addr_in_eax=0
468 SYM_CODE_START_NOALIGN(\name)
469 pushl %eax
470 pushl %ecx
471 pushl %edx
472
473 .if \put_ret_addr_in_eax
474 /* Place EIP in the arg1 */
475 movl 3*4(%esp), %eax
476 .endif
477
478 call \func
479 popl %edx
480 popl %ecx
481 popl %eax
482 RET
483 _ASM_NOKPROBE(\name)
484 SYM_CODE_END(\name)
485 .endm
486
487 #endif
488
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