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1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Compatibility mode system call entry point for x86-64.
4 *
5 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
6 */
7#include "calling.h"
8#include <asm/asm-offsets.h>
9#include <asm/current.h>
10#include <asm/errno.h>
11#include <asm/ia32_unistd.h>
12#include <asm/thread_info.h>
13#include <asm/segment.h>
14#include <asm/irqflags.h>
15#include <asm/asm.h>
16#include <asm/smap.h>
17#include <linux/linkage.h>
18#include <linux/err.h>
19
20 .section .entry.text, "ax"
21
22/*
23 * 32-bit SYSENTER entry.
24 *
25 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
26 * on 64-bit kernels running on Intel CPUs.
27 *
28 * The SYSENTER instruction, in principle, should *only* occur in the
29 * vDSO. In practice, a small number of Android devices were shipped
30 * with a copy of Bionic that inlined a SYSENTER instruction. This
31 * never happened in any of Google's Bionic versions -- it only happened
32 * in a narrow range of Intel-provided versions.
33 *
34 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
35 * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
36 * SYSENTER does not save anything on the stack,
37 * and does not save old RIP (!!!), RSP, or RFLAGS.
38 *
39 * Arguments:
40 * eax system call number
41 * ebx arg1
42 * ecx arg2
43 * edx arg3
44 * esi arg4
45 * edi arg5
46 * ebp user stack
47 * 0(%ebp) arg6
48 */
49ENTRY(entry_SYSENTER_compat)
50 /* Interrupts are off on entry. */
51 SWAPGS
52
53 /* We are about to clobber %rsp anyway, clobbering here is OK */
54 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
55
56 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
57
58 /*
59 * User tracing code (ptrace or signal handlers) might assume that
60 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
61 * syscall. Just in case the high bits are nonzero, zero-extend
62 * the syscall number. (This could almost certainly be deleted
63 * with no ill effects.)
64 */
65 movl %eax, %eax
66
67 /* Construct struct pt_regs on stack */
68 pushq $__USER32_DS /* pt_regs->ss */
69 pushq %rbp /* pt_regs->sp (stashed in bp) */
70
71 /*
72 * Push flags. This is nasty. First, interrupts are currently
73 * off, but we need pt_regs->flags to have IF set. Second, even
74 * if TF was set when SYSENTER started, it's clear by now. We fix
75 * that later using TIF_SINGLESTEP.
76 */
77 pushfq /* pt_regs->flags (except IF = 0) */
78 orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
79 pushq $__USER32_CS /* pt_regs->cs */
80 pushq $0 /* pt_regs->ip = 0 (placeholder) */
81 pushq %rax /* pt_regs->orig_ax */
82 pushq %rdi /* pt_regs->di */
83 pushq %rsi /* pt_regs->si */
84 pushq %rdx /* pt_regs->dx */
85 pushq %rcx /* pt_regs->cx */
86 pushq $-ENOSYS /* pt_regs->ax */
87 pushq $0 /* pt_regs->r8 = 0 */
88 xorl %r8d, %r8d /* nospec r8 */
89 pushq $0 /* pt_regs->r9 = 0 */
90 xorl %r9d, %r9d /* nospec r9 */
91 pushq $0 /* pt_regs->r10 = 0 */
92 xorl %r10d, %r10d /* nospec r10 */
93 pushq $0 /* pt_regs->r11 = 0 */
94 xorl %r11d, %r11d /* nospec r11 */
95 pushq %rbx /* pt_regs->rbx */
96 xorl %ebx, %ebx /* nospec rbx */
97 pushq %rbp /* pt_regs->rbp (will be overwritten) */
98 xorl %ebp, %ebp /* nospec rbp */
99 pushq $0 /* pt_regs->r12 = 0 */
100 xorl %r12d, %r12d /* nospec r12 */
101 pushq $0 /* pt_regs->r13 = 0 */
102 xorl %r13d, %r13d /* nospec r13 */
103 pushq $0 /* pt_regs->r14 = 0 */
104 xorl %r14d, %r14d /* nospec r14 */
105 pushq $0 /* pt_regs->r15 = 0 */
106 xorl %r15d, %r15d /* nospec r15 */
107 cld
108
109 /*
110 * SYSENTER doesn't filter flags, so we need to clear NT and AC
111 * ourselves. To save a few cycles, we can check whether
112 * either was set instead of doing an unconditional popfq.
113 * This needs to happen before enabling interrupts so that
114 * we don't get preempted with NT set.
115 *
116 * If TF is set, we will single-step all the way to here -- do_debug
117 * will ignore all the traps. (Yes, this is slow, but so is
118 * single-stepping in general. This allows us to avoid having
119 * a more complicated code to handle the case where a user program
120 * forces us to single-step through the SYSENTER entry code.)
121 *
122 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
123 * out-of-line as an optimization: NT is unlikely to be set in the
124 * majority of the cases and instead of polluting the I$ unnecessarily,
125 * we're keeping that code behind a branch which will predict as
126 * not-taken and therefore its instructions won't be fetched.
127 */
128 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
129 jnz .Lsysenter_fix_flags
130.Lsysenter_flags_fixed:
131
132 /*
133 * User mode is traced as though IRQs are on, and SYSENTER
134 * turned them off.
135 */
136 TRACE_IRQS_OFF
137
138 movq %rsp, %rdi
139 call do_fast_syscall_32
140 /* XEN PV guests always use IRET path */
141 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
142 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
143 jmp sysret32_from_system_call
144
145.Lsysenter_fix_flags:
146 pushq $X86_EFLAGS_FIXED
147 popfq
148 jmp .Lsysenter_flags_fixed
149GLOBAL(__end_entry_SYSENTER_compat)
150ENDPROC(entry_SYSENTER_compat)
151
152/*
153 * 32-bit SYSCALL entry.
154 *
155 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
156 * on 64-bit kernels running on AMD CPUs.
157 *
158 * The SYSCALL instruction, in principle, should *only* occur in the
159 * vDSO. In practice, it appears that this really is the case.
160 * As evidence:
161 *
162 * - The calling convention for SYSCALL has changed several times without
163 * anyone noticing.
164 *
165 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
166 * user task that did SYSCALL without immediately reloading SS
167 * would randomly crash.
168 *
169 * - Most programmers do not directly target AMD CPUs, and the 32-bit
170 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD
171 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
172 * because the SYSCALL instruction in legacy/native 32-bit mode (as
173 * opposed to compat mode) is sufficiently poorly designed as to be
174 * essentially unusable.
175 *
176 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
177 * RFLAGS to R11, then loads new SS, CS, and RIP from previously
178 * programmed MSRs. RFLAGS gets masked by a value from another MSR
179 * (so CLD and CLAC are not needed). SYSCALL does not save anything on
180 * the stack and does not change RSP.
181 *
182 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
183 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
184 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
185 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
186 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
187 *
188 * Arguments:
189 * eax system call number
190 * ecx return address
191 * ebx arg1
192 * ebp arg2 (note: not saved in the stack frame, should not be touched)
193 * edx arg3
194 * esi arg4
195 * edi arg5
196 * esp user stack
197 * 0(%esp) arg6
198 */
199ENTRY(entry_SYSCALL_compat)
200 /* Interrupts are off on entry. */
201 swapgs
202
203 /* Stash user ESP */
204 movl %esp, %r8d
205
206 /* Use %rsp as scratch reg. User ESP is stashed in r8 */
207 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
208
209 /* Switch to the kernel stack */
210 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
211
212 /* Construct struct pt_regs on stack */
213 pushq $__USER32_DS /* pt_regs->ss */
214 pushq %r8 /* pt_regs->sp */
215 pushq %r11 /* pt_regs->flags */
216 pushq $__USER32_CS /* pt_regs->cs */
217 pushq %rcx /* pt_regs->ip */
218GLOBAL(entry_SYSCALL_compat_after_hwframe)
219 movl %eax, %eax /* discard orig_ax high bits */
220 pushq %rax /* pt_regs->orig_ax */
221 pushq %rdi /* pt_regs->di */
222 pushq %rsi /* pt_regs->si */
223 xorl %esi, %esi /* nospec si */
224 pushq %rdx /* pt_regs->dx */
225 xorl %edx, %edx /* nospec dx */
226 pushq %rbp /* pt_regs->cx (stashed in bp) */
227 xorl %ecx, %ecx /* nospec cx */
228 pushq $-ENOSYS /* pt_regs->ax */
229 pushq $0 /* pt_regs->r8 = 0 */
230 xorl %r8d, %r8d /* nospec r8 */
231 pushq $0 /* pt_regs->r9 = 0 */
232 xorl %r9d, %r9d /* nospec r9 */
233 pushq $0 /* pt_regs->r10 = 0 */
234 xorl %r10d, %r10d /* nospec r10 */
235 pushq $0 /* pt_regs->r11 = 0 */
236 xorl %r11d, %r11d /* nospec r11 */
237 pushq %rbx /* pt_regs->rbx */
238 xorl %ebx, %ebx /* nospec rbx */
239 pushq %rbp /* pt_regs->rbp (will be overwritten) */
240 xorl %ebp, %ebp /* nospec rbp */
241 pushq $0 /* pt_regs->r12 = 0 */
242 xorl %r12d, %r12d /* nospec r12 */
243 pushq $0 /* pt_regs->r13 = 0 */
244 xorl %r13d, %r13d /* nospec r13 */
245 pushq $0 /* pt_regs->r14 = 0 */
246 xorl %r14d, %r14d /* nospec r14 */
247 pushq $0 /* pt_regs->r15 = 0 */
248 xorl %r15d, %r15d /* nospec r15 */
249
250 /*
251 * User mode is traced as though IRQs are on, and SYSENTER
252 * turned them off.
253 */
254 TRACE_IRQS_OFF
255
256 movq %rsp, %rdi
257 call do_fast_syscall_32
258 /* XEN PV guests always use IRET path */
259 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
260 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
261
262 /* Opportunistic SYSRET */
263sysret32_from_system_call:
264 /*
265 * We are not going to return to userspace from the trampoline
266 * stack. So let's erase the thread stack right now.
267 */
268 STACKLEAK_ERASE
269 TRACE_IRQS_ON /* User mode traces as IRQs on. */
270 movq RBX(%rsp), %rbx /* pt_regs->rbx */
271 movq RBP(%rsp), %rbp /* pt_regs->rbp */
272 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
273 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
274 addq $RAX, %rsp /* Skip r8-r15 */
275 popq %rax /* pt_regs->rax */
276 popq %rdx /* Skip pt_regs->cx */
277 popq %rdx /* pt_regs->dx */
278 popq %rsi /* pt_regs->si */
279 popq %rdi /* pt_regs->di */
280
281 /*
282 * USERGS_SYSRET32 does:
283 * GSBASE = user's GS base
284 * EIP = ECX
285 * RFLAGS = R11
286 * CS = __USER32_CS
287 * SS = __USER_DS
288 *
289 * ECX will not match pt_regs->cx, but we're returning to a vDSO
290 * trampoline that will fix up RCX, so this is okay.
291 *
292 * R12-R15 are callee-saved, so they contain whatever was in them
293 * when the system call started, which is already known to user
294 * code. We zero R8-R10 to avoid info leaks.
295 */
296 movq RSP-ORIG_RAX(%rsp), %rsp
297
298 /*
299 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
300 * on the process stack which is not mapped to userspace and
301 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3
302 * switch until after after the last reference to the process
303 * stack.
304 *
305 * %r8/%r9 are zeroed before the sysret, thus safe to clobber.
306 */
307 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
308
309 xorl %r8d, %r8d
310 xorl %r9d, %r9d
311 xorl %r10d, %r10d
312 swapgs
313 sysretl
314END(entry_SYSCALL_compat)
315
316/*
317 * 32-bit legacy system call entry.
318 *
319 * 32-bit x86 Linux system calls traditionally used the INT $0x80
320 * instruction. INT $0x80 lands here.
321 *
322 * This entry point can be used by 32-bit and 64-bit programs to perform
323 * 32-bit system calls. Instances of INT $0x80 can be found inline in
324 * various programs and libraries. It is also used by the vDSO's
325 * __kernel_vsyscall fallback for hardware that doesn't support a faster
326 * entry method. Restarted 32-bit system calls also fall back to INT
327 * $0x80 regardless of what instruction was originally used to do the
328 * system call.
329 *
330 * This is considered a slow path. It is not used by most libc
331 * implementations on modern hardware except during process startup.
332 *
333 * Arguments:
334 * eax system call number
335 * ebx arg1
336 * ecx arg2
337 * edx arg3
338 * esi arg4
339 * edi arg5
340 * ebp arg6
341 */
342ENTRY(entry_INT80_compat)
343 /*
344 * Interrupts are off on entry.
345 */
346 ASM_CLAC /* Do this early to minimize exposure */
347 SWAPGS
348
349 /*
350 * User tracing code (ptrace or signal handlers) might assume that
351 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
352 * syscall. Just in case the high bits are nonzero, zero-extend
353 * the syscall number. (This could almost certainly be deleted
354 * with no ill effects.)
355 */
356 movl %eax, %eax
357
358 /* switch to thread stack expects orig_ax and rdi to be pushed */
359 pushq %rax /* pt_regs->orig_ax */
360 pushq %rdi /* pt_regs->di */
361
362 /* Need to switch before accessing the thread stack. */
363 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
364 /* In the Xen PV case we already run on the thread stack. */
365 ALTERNATIVE "movq %rsp, %rdi", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
366 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
367
368 pushq 6*8(%rdi) /* regs->ss */
369 pushq 5*8(%rdi) /* regs->rsp */
370 pushq 4*8(%rdi) /* regs->eflags */
371 pushq 3*8(%rdi) /* regs->cs */
372 pushq 2*8(%rdi) /* regs->ip */
373 pushq 1*8(%rdi) /* regs->orig_ax */
374 pushq (%rdi) /* pt_regs->di */
375.Lint80_keep_stack:
376
377 pushq %rsi /* pt_regs->si */
378 xorl %esi, %esi /* nospec si */
379 pushq %rdx /* pt_regs->dx */
380 xorl %edx, %edx /* nospec dx */
381 pushq %rcx /* pt_regs->cx */
382 xorl %ecx, %ecx /* nospec cx */
383 pushq $-ENOSYS /* pt_regs->ax */
384 pushq %r8 /* pt_regs->r8 */
385 xorl %r8d, %r8d /* nospec r8 */
386 pushq %r9 /* pt_regs->r9 */
387 xorl %r9d, %r9d /* nospec r9 */
388 pushq %r10 /* pt_regs->r10*/
389 xorl %r10d, %r10d /* nospec r10 */
390 pushq %r11 /* pt_regs->r11 */
391 xorl %r11d, %r11d /* nospec r11 */
392 pushq %rbx /* pt_regs->rbx */
393 xorl %ebx, %ebx /* nospec rbx */
394 pushq %rbp /* pt_regs->rbp */
395 xorl %ebp, %ebp /* nospec rbp */
396 pushq %r12 /* pt_regs->r12 */
397 xorl %r12d, %r12d /* nospec r12 */
398 pushq %r13 /* pt_regs->r13 */
399 xorl %r13d, %r13d /* nospec r13 */
400 pushq %r14 /* pt_regs->r14 */
401 xorl %r14d, %r14d /* nospec r14 */
402 pushq %r15 /* pt_regs->r15 */
403 xorl %r15d, %r15d /* nospec r15 */
404 cld
405
406 /*
407 * User mode is traced as though IRQs are on, and the interrupt
408 * gate turned them off.
409 */
410 TRACE_IRQS_OFF
411
412 movq %rsp, %rdi
413 call do_int80_syscall_32
414.Lsyscall_32_done:
415
416 /* Go back to user mode. */
417 TRACE_IRQS_ON
418 jmp swapgs_restore_regs_and_return_to_usermode
419END(entry_INT80_compat)
1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Compatibility mode system call entry point for x86-64.
4 *
5 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
6 */
7#include "calling.h"
8#include <asm/asm-offsets.h>
9#include <asm/current.h>
10#include <asm/errno.h>
11#include <asm/ia32_unistd.h>
12#include <asm/thread_info.h>
13#include <asm/segment.h>
14#include <asm/irqflags.h>
15#include <asm/asm.h>
16#include <asm/smap.h>
17#include <linux/linkage.h>
18#include <linux/err.h>
19
20 .section .entry.text, "ax"
21
22/*
23 * 32-bit SYSENTER entry.
24 *
25 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
26 * on 64-bit kernels running on Intel CPUs.
27 *
28 * The SYSENTER instruction, in principle, should *only* occur in the
29 * vDSO. In practice, a small number of Android devices were shipped
30 * with a copy of Bionic that inlined a SYSENTER instruction. This
31 * never happened in any of Google's Bionic versions -- it only happened
32 * in a narrow range of Intel-provided versions.
33 *
34 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
35 * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
36 * SYSENTER does not save anything on the stack,
37 * and does not save old RIP (!!!), RSP, or RFLAGS.
38 *
39 * Arguments:
40 * eax system call number
41 * ebx arg1
42 * ecx arg2
43 * edx arg3
44 * esi arg4
45 * edi arg5
46 * ebp user stack
47 * 0(%ebp) arg6
48 */
49SYM_CODE_START(entry_SYSENTER_compat)
50 UNWIND_HINT_EMPTY
51 /* Interrupts are off on entry. */
52 SWAPGS
53
54 pushq %rax
55 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
56 popq %rax
57
58 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
59
60 /* Construct struct pt_regs on stack */
61 pushq $__USER32_DS /* pt_regs->ss */
62 pushq $0 /* pt_regs->sp = 0 (placeholder) */
63
64 /*
65 * Push flags. This is nasty. First, interrupts are currently
66 * off, but we need pt_regs->flags to have IF set. Second, if TS
67 * was set in usermode, it's still set, and we're singlestepping
68 * through this code. do_SYSENTER_32() will fix up IF.
69 */
70 pushfq /* pt_regs->flags (except IF = 0) */
71 pushq $__USER32_CS /* pt_regs->cs */
72 pushq $0 /* pt_regs->ip = 0 (placeholder) */
73SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
74
75 /*
76 * User tracing code (ptrace or signal handlers) might assume that
77 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
78 * syscall. Just in case the high bits are nonzero, zero-extend
79 * the syscall number. (This could almost certainly be deleted
80 * with no ill effects.)
81 */
82 movl %eax, %eax
83
84 pushq %rax /* pt_regs->orig_ax */
85 pushq %rdi /* pt_regs->di */
86 pushq %rsi /* pt_regs->si */
87 pushq %rdx /* pt_regs->dx */
88 pushq %rcx /* pt_regs->cx */
89 pushq $-ENOSYS /* pt_regs->ax */
90 pushq $0 /* pt_regs->r8 = 0 */
91 xorl %r8d, %r8d /* nospec r8 */
92 pushq $0 /* pt_regs->r9 = 0 */
93 xorl %r9d, %r9d /* nospec r9 */
94 pushq $0 /* pt_regs->r10 = 0 */
95 xorl %r10d, %r10d /* nospec r10 */
96 pushq $0 /* pt_regs->r11 = 0 */
97 xorl %r11d, %r11d /* nospec r11 */
98 pushq %rbx /* pt_regs->rbx */
99 xorl %ebx, %ebx /* nospec rbx */
100 pushq %rbp /* pt_regs->rbp (will be overwritten) */
101 xorl %ebp, %ebp /* nospec rbp */
102 pushq $0 /* pt_regs->r12 = 0 */
103 xorl %r12d, %r12d /* nospec r12 */
104 pushq $0 /* pt_regs->r13 = 0 */
105 xorl %r13d, %r13d /* nospec r13 */
106 pushq $0 /* pt_regs->r14 = 0 */
107 xorl %r14d, %r14d /* nospec r14 */
108 pushq $0 /* pt_regs->r15 = 0 */
109 xorl %r15d, %r15d /* nospec r15 */
110
111 UNWIND_HINT_REGS
112
113 cld
114
115 /*
116 * SYSENTER doesn't filter flags, so we need to clear NT and AC
117 * ourselves. To save a few cycles, we can check whether
118 * either was set instead of doing an unconditional popfq.
119 * This needs to happen before enabling interrupts so that
120 * we don't get preempted with NT set.
121 *
122 * If TF is set, we will single-step all the way to here -- do_debug
123 * will ignore all the traps. (Yes, this is slow, but so is
124 * single-stepping in general. This allows us to avoid having
125 * a more complicated code to handle the case where a user program
126 * forces us to single-step through the SYSENTER entry code.)
127 *
128 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
129 * out-of-line as an optimization: NT is unlikely to be set in the
130 * majority of the cases and instead of polluting the I$ unnecessarily,
131 * we're keeping that code behind a branch which will predict as
132 * not-taken and therefore its instructions won't be fetched.
133 */
134 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
135 jnz .Lsysenter_fix_flags
136.Lsysenter_flags_fixed:
137
138 movq %rsp, %rdi
139 call do_SYSENTER_32
140 /* XEN PV guests always use IRET path */
141 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
142 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
143 jmp sysret32_from_system_call
144
145.Lsysenter_fix_flags:
146 pushq $X86_EFLAGS_FIXED
147 popfq
148 jmp .Lsysenter_flags_fixed
149SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
150SYM_CODE_END(entry_SYSENTER_compat)
151
152/*
153 * 32-bit SYSCALL entry.
154 *
155 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
156 * on 64-bit kernels running on AMD CPUs.
157 *
158 * The SYSCALL instruction, in principle, should *only* occur in the
159 * vDSO. In practice, it appears that this really is the case.
160 * As evidence:
161 *
162 * - The calling convention for SYSCALL has changed several times without
163 * anyone noticing.
164 *
165 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
166 * user task that did SYSCALL without immediately reloading SS
167 * would randomly crash.
168 *
169 * - Most programmers do not directly target AMD CPUs, and the 32-bit
170 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD
171 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
172 * because the SYSCALL instruction in legacy/native 32-bit mode (as
173 * opposed to compat mode) is sufficiently poorly designed as to be
174 * essentially unusable.
175 *
176 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
177 * RFLAGS to R11, then loads new SS, CS, and RIP from previously
178 * programmed MSRs. RFLAGS gets masked by a value from another MSR
179 * (so CLD and CLAC are not needed). SYSCALL does not save anything on
180 * the stack and does not change RSP.
181 *
182 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
183 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
184 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
185 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
186 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
187 *
188 * Arguments:
189 * eax system call number
190 * ecx return address
191 * ebx arg1
192 * ebp arg2 (note: not saved in the stack frame, should not be touched)
193 * edx arg3
194 * esi arg4
195 * edi arg5
196 * esp user stack
197 * 0(%esp) arg6
198 */
199SYM_CODE_START(entry_SYSCALL_compat)
200 UNWIND_HINT_EMPTY
201 /* Interrupts are off on entry. */
202 swapgs
203
204 /* Stash user ESP */
205 movl %esp, %r8d
206
207 /* Use %rsp as scratch reg. User ESP is stashed in r8 */
208 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
209
210 /* Switch to the kernel stack */
211 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
212
213SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
214
215 /* Construct struct pt_regs on stack */
216 pushq $__USER32_DS /* pt_regs->ss */
217 pushq %r8 /* pt_regs->sp */
218 pushq %r11 /* pt_regs->flags */
219 pushq $__USER32_CS /* pt_regs->cs */
220 pushq %rcx /* pt_regs->ip */
221SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
222 movl %eax, %eax /* discard orig_ax high bits */
223 pushq %rax /* pt_regs->orig_ax */
224 pushq %rdi /* pt_regs->di */
225 pushq %rsi /* pt_regs->si */
226 xorl %esi, %esi /* nospec si */
227 pushq %rdx /* pt_regs->dx */
228 xorl %edx, %edx /* nospec dx */
229 pushq %rbp /* pt_regs->cx (stashed in bp) */
230 xorl %ecx, %ecx /* nospec cx */
231 pushq $-ENOSYS /* pt_regs->ax */
232 pushq $0 /* pt_regs->r8 = 0 */
233 xorl %r8d, %r8d /* nospec r8 */
234 pushq $0 /* pt_regs->r9 = 0 */
235 xorl %r9d, %r9d /* nospec r9 */
236 pushq $0 /* pt_regs->r10 = 0 */
237 xorl %r10d, %r10d /* nospec r10 */
238 pushq $0 /* pt_regs->r11 = 0 */
239 xorl %r11d, %r11d /* nospec r11 */
240 pushq %rbx /* pt_regs->rbx */
241 xorl %ebx, %ebx /* nospec rbx */
242 pushq %rbp /* pt_regs->rbp (will be overwritten) */
243 xorl %ebp, %ebp /* nospec rbp */
244 pushq $0 /* pt_regs->r12 = 0 */
245 xorl %r12d, %r12d /* nospec r12 */
246 pushq $0 /* pt_regs->r13 = 0 */
247 xorl %r13d, %r13d /* nospec r13 */
248 pushq $0 /* pt_regs->r14 = 0 */
249 xorl %r14d, %r14d /* nospec r14 */
250 pushq $0 /* pt_regs->r15 = 0 */
251 xorl %r15d, %r15d /* nospec r15 */
252
253 UNWIND_HINT_REGS
254
255 movq %rsp, %rdi
256 call do_fast_syscall_32
257 /* XEN PV guests always use IRET path */
258 ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
259 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
260
261 /* Opportunistic SYSRET */
262sysret32_from_system_call:
263 /*
264 * We are not going to return to userspace from the trampoline
265 * stack. So let's erase the thread stack right now.
266 */
267 STACKLEAK_ERASE
268
269 movq RBX(%rsp), %rbx /* pt_regs->rbx */
270 movq RBP(%rsp), %rbp /* pt_regs->rbp */
271 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
272 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
273 addq $RAX, %rsp /* Skip r8-r15 */
274 popq %rax /* pt_regs->rax */
275 popq %rdx /* Skip pt_regs->cx */
276 popq %rdx /* pt_regs->dx */
277 popq %rsi /* pt_regs->si */
278 popq %rdi /* pt_regs->di */
279
280 /*
281 * USERGS_SYSRET32 does:
282 * GSBASE = user's GS base
283 * EIP = ECX
284 * RFLAGS = R11
285 * CS = __USER32_CS
286 * SS = __USER_DS
287 *
288 * ECX will not match pt_regs->cx, but we're returning to a vDSO
289 * trampoline that will fix up RCX, so this is okay.
290 *
291 * R12-R15 are callee-saved, so they contain whatever was in them
292 * when the system call started, which is already known to user
293 * code. We zero R8-R10 to avoid info leaks.
294 */
295 movq RSP-ORIG_RAX(%rsp), %rsp
296
297 /*
298 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
299 * on the process stack which is not mapped to userspace and
300 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3
301 * switch until after after the last reference to the process
302 * stack.
303 *
304 * %r8/%r9 are zeroed before the sysret, thus safe to clobber.
305 */
306 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
307
308 xorl %r8d, %r8d
309 xorl %r9d, %r9d
310 xorl %r10d, %r10d
311 swapgs
312 sysretl
313SYM_CODE_END(entry_SYSCALL_compat)
314
315/*
316 * 32-bit legacy system call entry.
317 *
318 * 32-bit x86 Linux system calls traditionally used the INT $0x80
319 * instruction. INT $0x80 lands here.
320 *
321 * This entry point can be used by 32-bit and 64-bit programs to perform
322 * 32-bit system calls. Instances of INT $0x80 can be found inline in
323 * various programs and libraries. It is also used by the vDSO's
324 * __kernel_vsyscall fallback for hardware that doesn't support a faster
325 * entry method. Restarted 32-bit system calls also fall back to INT
326 * $0x80 regardless of what instruction was originally used to do the
327 * system call.
328 *
329 * This is considered a slow path. It is not used by most libc
330 * implementations on modern hardware except during process startup.
331 *
332 * Arguments:
333 * eax system call number
334 * ebx arg1
335 * ecx arg2
336 * edx arg3
337 * esi arg4
338 * edi arg5
339 * ebp arg6
340 */
341SYM_CODE_START(entry_INT80_compat)
342 UNWIND_HINT_EMPTY
343 /*
344 * Interrupts are off on entry.
345 */
346 ASM_CLAC /* Do this early to minimize exposure */
347 SWAPGS
348
349 /*
350 * User tracing code (ptrace or signal handlers) might assume that
351 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
352 * syscall. Just in case the high bits are nonzero, zero-extend
353 * the syscall number. (This could almost certainly be deleted
354 * with no ill effects.)
355 */
356 movl %eax, %eax
357
358 /* switch to thread stack expects orig_ax and rdi to be pushed */
359 pushq %rax /* pt_regs->orig_ax */
360 pushq %rdi /* pt_regs->di */
361
362 /* Need to switch before accessing the thread stack. */
363 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
364
365 /* In the Xen PV case we already run on the thread stack. */
366 ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
367
368 movq %rsp, %rdi
369 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
370
371 pushq 6*8(%rdi) /* regs->ss */
372 pushq 5*8(%rdi) /* regs->rsp */
373 pushq 4*8(%rdi) /* regs->eflags */
374 pushq 3*8(%rdi) /* regs->cs */
375 pushq 2*8(%rdi) /* regs->ip */
376 pushq 1*8(%rdi) /* regs->orig_ax */
377 pushq (%rdi) /* pt_regs->di */
378.Lint80_keep_stack:
379
380 pushq %rsi /* pt_regs->si */
381 xorl %esi, %esi /* nospec si */
382 pushq %rdx /* pt_regs->dx */
383 xorl %edx, %edx /* nospec dx */
384 pushq %rcx /* pt_regs->cx */
385 xorl %ecx, %ecx /* nospec cx */
386 pushq $-ENOSYS /* pt_regs->ax */
387 pushq %r8 /* pt_regs->r8 */
388 xorl %r8d, %r8d /* nospec r8 */
389 pushq %r9 /* pt_regs->r9 */
390 xorl %r9d, %r9d /* nospec r9 */
391 pushq %r10 /* pt_regs->r10*/
392 xorl %r10d, %r10d /* nospec r10 */
393 pushq %r11 /* pt_regs->r11 */
394 xorl %r11d, %r11d /* nospec r11 */
395 pushq %rbx /* pt_regs->rbx */
396 xorl %ebx, %ebx /* nospec rbx */
397 pushq %rbp /* pt_regs->rbp */
398 xorl %ebp, %ebp /* nospec rbp */
399 pushq %r12 /* pt_regs->r12 */
400 xorl %r12d, %r12d /* nospec r12 */
401 pushq %r13 /* pt_regs->r13 */
402 xorl %r13d, %r13d /* nospec r13 */
403 pushq %r14 /* pt_regs->r14 */
404 xorl %r14d, %r14d /* nospec r14 */
405 pushq %r15 /* pt_regs->r15 */
406 xorl %r15d, %r15d /* nospec r15 */
407
408 UNWIND_HINT_REGS
409
410 cld
411
412 movq %rsp, %rdi
413 call do_int80_syscall_32
414 jmp swapgs_restore_regs_and_return_to_usermode
415SYM_CODE_END(entry_INT80_compat)