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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
36For 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
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 UNWIND_HINT_REGS
91
92 .if \save_ret
93 pushq %rsi /* return address on top of stack */
94 .endif
95.endm
96
97.macro CLEAR_REGS
98 /*
99 * Sanitize registers of values that a speculation attack might
100 * otherwise want to exploit. The lower registers are likely clobbered
101 * well before they could be put to use in a speculative execution
102 * gadget.
103 */
104 xorl %esi, %esi /* nospec si */
105 xorl %edx, %edx /* nospec dx */
106 xorl %ecx, %ecx /* nospec cx */
107 xorl %r8d, %r8d /* nospec r8 */
108 xorl %r9d, %r9d /* nospec r9 */
109 xorl %r10d, %r10d /* nospec r10 */
110 xorl %r11d, %r11d /* nospec r11 */
111 xorl %ebx, %ebx /* nospec rbx */
112 xorl %ebp, %ebp /* nospec rbp */
113 xorl %r12d, %r12d /* nospec r12 */
114 xorl %r13d, %r13d /* nospec r13 */
115 xorl %r14d, %r14d /* nospec r14 */
116 xorl %r15d, %r15d /* nospec r15 */
117
118.endm
119
120.macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0
121 PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret
122 CLEAR_REGS
123.endm
124
125.macro POP_REGS pop_rdi=1
126 popq %r15
127 popq %r14
128 popq %r13
129 popq %r12
130 popq %rbp
131 popq %rbx
132 popq %r11
133 popq %r10
134 popq %r9
135 popq %r8
136 popq %rax
137 popq %rcx
138 popq %rdx
139 popq %rsi
140 .if \pop_rdi
141 popq %rdi
142 .endif
143.endm
144
145#ifdef CONFIG_PAGE_TABLE_ISOLATION
146
147/*
148 * PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two
149 * halves:
150 */
151#define PTI_USER_PGTABLE_BIT PAGE_SHIFT
152#define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT)
153#define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT
154#define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT)
155#define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK)
156
157.macro SET_NOFLUSH_BIT reg:req
158 bts $X86_CR3_PCID_NOFLUSH_BIT, \reg
159.endm
160
161.macro ADJUST_KERNEL_CR3 reg:req
162 ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID
163 /* Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */
164 andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg
165.endm
166
167.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
168 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
169 mov %cr3, \scratch_reg
170 ADJUST_KERNEL_CR3 \scratch_reg
171 mov \scratch_reg, %cr3
172.Lend_\@:
173.endm
174
175#define THIS_CPU_user_pcid_flush_mask \
176 PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask
177
178.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
179 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
180 mov %cr3, \scratch_reg
181
182 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
183
184 /*
185 * Test if the ASID needs a flush.
186 */
187 movq \scratch_reg, \scratch_reg2
188 andq $(0x7FF), \scratch_reg /* mask ASID */
189 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
190 jnc .Lnoflush_\@
191
192 /* Flush needed, clear the bit */
193 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
194 movq \scratch_reg2, \scratch_reg
195 jmp .Lwrcr3_pcid_\@
196
197.Lnoflush_\@:
198 movq \scratch_reg2, \scratch_reg
199 SET_NOFLUSH_BIT \scratch_reg
200
201.Lwrcr3_pcid_\@:
202 /* Flip the ASID to the user version */
203 orq $(PTI_USER_PCID_MASK), \scratch_reg
204
205.Lwrcr3_\@:
206 /* Flip the PGD to the user version */
207 orq $(PTI_USER_PGTABLE_MASK), \scratch_reg
208 mov \scratch_reg, %cr3
209.Lend_\@:
210.endm
211
212.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
213 pushq %rax
214 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax
215 popq %rax
216.endm
217
218.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
219 ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI
220 movq %cr3, \scratch_reg
221 movq \scratch_reg, \save_reg
222 /*
223 * Test the user pagetable bit. If set, then the user page tables
224 * are active. If clear CR3 already has the kernel page table
225 * active.
226 */
227 bt $PTI_USER_PGTABLE_BIT, \scratch_reg
228 jnc .Ldone_\@
229
230 ADJUST_KERNEL_CR3 \scratch_reg
231 movq \scratch_reg, %cr3
232
233.Ldone_\@:
234.endm
235
236.macro RESTORE_CR3 scratch_reg:req save_reg:req
237 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
238
239 ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
240
241 /*
242 * KERNEL pages can always resume with NOFLUSH as we do
243 * explicit flushes.
244 */
245 bt $PTI_USER_PGTABLE_BIT, \save_reg
246 jnc .Lnoflush_\@
247
248 /*
249 * Check if there's a pending flush for the user ASID we're
250 * about to set.
251 */
252 movq \save_reg, \scratch_reg
253 andq $(0x7FF), \scratch_reg
254 bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
255 jnc .Lnoflush_\@
256
257 btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
258 jmp .Lwrcr3_\@
259
260.Lnoflush_\@:
261 SET_NOFLUSH_BIT \save_reg
262
263.Lwrcr3_\@:
264 /*
265 * The CR3 write could be avoided when not changing its value,
266 * but would require a CR3 read *and* a scratch register.
267 */
268 movq \save_reg, %cr3
269.Lend_\@:
270.endm
271
272#else /* CONFIG_PAGE_TABLE_ISOLATION=n: */
273
274.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
275.endm
276.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
277.endm
278.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
279.endm
280.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
281.endm
282.macro RESTORE_CR3 scratch_reg:req save_reg:req
283.endm
284
285#endif
286
287/*
288 * IBRS kernel mitigation for Spectre_v2.
289 *
290 * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
291 * the regs it uses (AX, CX, DX). Must be called before the first RET
292 * instruction (NOTE! UNTRAIN_RET includes a RET instruction)
293 *
294 * The optional argument is used to save/restore the current value,
295 * which is used on the paranoid paths.
296 *
297 * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
298 */
299.macro IBRS_ENTER save_reg
300#ifdef CONFIG_CPU_IBRS_ENTRY
301 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
302 movl $MSR_IA32_SPEC_CTRL, %ecx
303
304.ifnb \save_reg
305 rdmsr
306 shl $32, %rdx
307 or %rdx, %rax
308 mov %rax, \save_reg
309 test $SPEC_CTRL_IBRS, %eax
310 jz .Ldo_wrmsr_\@
311 lfence
312 jmp .Lend_\@
313.Ldo_wrmsr_\@:
314.endif
315
316 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
317 movl %edx, %eax
318 shr $32, %rdx
319 wrmsr
320.Lend_\@:
321#endif
322.endm
323
324/*
325 * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
326 * regs. Must be called after the last RET.
327 */
328.macro IBRS_EXIT save_reg
329#ifdef CONFIG_CPU_IBRS_ENTRY
330 ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
331 movl $MSR_IA32_SPEC_CTRL, %ecx
332
333.ifnb \save_reg
334 mov \save_reg, %rdx
335.else
336 movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
337 andl $(~SPEC_CTRL_IBRS), %edx
338.endif
339
340 movl %edx, %eax
341 shr $32, %rdx
342 wrmsr
343.Lend_\@:
344#endif
345.endm
346
347/*
348 * Mitigate Spectre v1 for conditional swapgs code paths.
349 *
350 * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to
351 * prevent a speculative swapgs when coming from kernel space.
352 *
353 * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path,
354 * to prevent the swapgs from getting speculatively skipped when coming from
355 * user space.
356 */
357.macro FENCE_SWAPGS_USER_ENTRY
358 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER
359.endm
360.macro FENCE_SWAPGS_KERNEL_ENTRY
361 ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL
362.endm
363
364.macro STACKLEAK_ERASE_NOCLOBBER
365#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
366 PUSH_AND_CLEAR_REGS
367 call stackleak_erase
368 POP_REGS
369#endif
370.endm
371
372.macro SAVE_AND_SET_GSBASE scratch_reg:req save_reg:req
373 rdgsbase \save_reg
374 GET_PERCPU_BASE \scratch_reg
375 wrgsbase \scratch_reg
376.endm
377
378#else /* CONFIG_X86_64 */
379# undef UNWIND_HINT_IRET_REGS
380# define UNWIND_HINT_IRET_REGS
381#endif /* !CONFIG_X86_64 */
382
383.macro STACKLEAK_ERASE
384#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
385 call stackleak_erase
386#endif
387.endm
388
389#ifdef CONFIG_SMP
390
391/*
392 * CPU/node NR is loaded from the limit (size) field of a special segment
393 * descriptor entry in GDT.
394 */
395.macro LOAD_CPU_AND_NODE_SEG_LIMIT reg:req
396 movq $__CPUNODE_SEG, \reg
397 lsl \reg, \reg
398.endm
399
400/*
401 * Fetch the per-CPU GSBASE value for this processor and put it in @reg.
402 * We normally use %gs for accessing per-CPU data, but we are setting up
403 * %gs here and obviously can not use %gs itself to access per-CPU data.
404 *
405 * Do not use RDPID, because KVM loads guest's TSC_AUX on vm-entry and
406 * may not restore the host's value until the CPU returns to userspace.
407 * Thus the kernel would consume a guest's TSC_AUX if an NMI arrives
408 * while running KVM's run loop.
409 */
410.macro GET_PERCPU_BASE reg:req
411 LOAD_CPU_AND_NODE_SEG_LIMIT \reg
412 andq $VDSO_CPUNODE_MASK, \reg
413 movq __per_cpu_offset(, \reg, 8), \reg
414.endm
415
416#else
417
418.macro GET_PERCPU_BASE reg:req
419 movq pcpu_unit_offsets(%rip), \reg
420.endm
421
422#endif /* CONFIG_SMP */