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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * common.c - C code for kernel entry and exit
4 * Copyright (c) 2015 Andrew Lutomirski
5 *
6 * Based on asm and ptrace code by many authors. The code here originated
7 * in ptrace.c and signal.c.
8 */
9
10#include <linux/kernel.h>
11#include <linux/sched.h>
12#include <linux/sched/task_stack.h>
13#include <linux/entry-common.h>
14#include <linux/mm.h>
15#include <linux/smp.h>
16#include <linux/errno.h>
17#include <linux/ptrace.h>
18#include <linux/export.h>
19#include <linux/nospec.h>
20#include <linux/syscalls.h>
21#include <linux/uaccess.h>
22
23#ifdef CONFIG_XEN_PV
24#include <xen/xen-ops.h>
25#include <xen/events.h>
26#endif
27
28#include <asm/desc.h>
29#include <asm/traps.h>
30#include <asm/vdso.h>
31#include <asm/cpufeature.h>
32#include <asm/fpu/api.h>
33#include <asm/nospec-branch.h>
34#include <asm/io_bitmap.h>
35#include <asm/syscall.h>
36#include <asm/irq_stack.h>
37
38#ifdef CONFIG_X86_64
39__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
40{
41 nr = syscall_enter_from_user_mode(regs, nr);
42
43 instrumentation_begin();
44 if (likely(nr < NR_syscalls)) {
45 nr = array_index_nospec(nr, NR_syscalls);
46 regs->ax = sys_call_table[nr](regs);
47#ifdef CONFIG_X86_X32_ABI
48 } else if (likely((nr & __X32_SYSCALL_BIT) &&
49 (nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
50 nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
51 X32_NR_syscalls);
52 regs->ax = x32_sys_call_table[nr](regs);
53#endif
54 }
55 instrumentation_end();
56 syscall_exit_to_user_mode(regs);
57}
58#endif
59
60#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
61static __always_inline unsigned int syscall_32_enter(struct pt_regs *regs)
62{
63 if (IS_ENABLED(CONFIG_IA32_EMULATION))
64 current_thread_info()->status |= TS_COMPAT;
65
66 return (unsigned int)regs->orig_ax;
67}
68
69/*
70 * Invoke a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL.
71 */
72static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs,
73 unsigned int nr)
74{
75 if (likely(nr < IA32_NR_syscalls)) {
76 instrumentation_begin();
77 nr = array_index_nospec(nr, IA32_NR_syscalls);
78 regs->ax = ia32_sys_call_table[nr](regs);
79 instrumentation_end();
80 }
81}
82
83/* Handles int $0x80 */
84__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
85{
86 unsigned int nr = syscall_32_enter(regs);
87
88 /*
89 * Subtlety here: if ptrace pokes something larger than 2^32-1 into
90 * orig_ax, the unsigned int return value truncates it. This may
91 * or may not be necessary, but it matches the old asm behavior.
92 */
93 nr = (unsigned int)syscall_enter_from_user_mode(regs, nr);
94
95 do_syscall_32_irqs_on(regs, nr);
96 syscall_exit_to_user_mode(regs);
97}
98
99static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
100{
101 unsigned int nr = syscall_32_enter(regs);
102 int res;
103
104 /*
105 * This cannot use syscall_enter_from_user_mode() as it has to
106 * fetch EBP before invoking any of the syscall entry work
107 * functions.
108 */
109 syscall_enter_from_user_mode_prepare(regs);
110
111 instrumentation_begin();
112 /* Fetch EBP from where the vDSO stashed it. */
113 if (IS_ENABLED(CONFIG_X86_64)) {
114 /*
115 * Micro-optimization: the pointer we're following is
116 * explicitly 32 bits, so it can't be out of range.
117 */
118 res = __get_user(*(u32 *)®s->bp,
119 (u32 __user __force *)(unsigned long)(u32)regs->sp);
120 } else {
121 res = get_user(*(u32 *)®s->bp,
122 (u32 __user __force *)(unsigned long)(u32)regs->sp);
123 }
124 instrumentation_end();
125
126 if (res) {
127 /* User code screwed up. */
128 regs->ax = -EFAULT;
129 syscall_exit_to_user_mode(regs);
130 return false;
131 }
132
133 /* The case truncates any ptrace induced syscall nr > 2^32 -1 */
134 nr = (unsigned int)syscall_enter_from_user_mode_work(regs, nr);
135
136 /* Now this is just like a normal syscall. */
137 do_syscall_32_irqs_on(regs, nr);
138 syscall_exit_to_user_mode(regs);
139 return true;
140}
141
142/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
143__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
144{
145 /*
146 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
147 * convention. Adjust regs so it looks like we entered using int80.
148 */
149 unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
150 vdso_image_32.sym_int80_landing_pad;
151
152 /*
153 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
154 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
155 * Fix it up.
156 */
157 regs->ip = landing_pad;
158
159 /* Invoke the syscall. If it failed, keep it simple: use IRET. */
160 if (!__do_fast_syscall_32(regs))
161 return 0;
162
163#ifdef CONFIG_X86_64
164 /*
165 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
166 * SYSRETL is available on all 64-bit CPUs, so we don't need to
167 * bother with SYSEXIT.
168 *
169 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
170 * because the ECX fixup above will ensure that this is essentially
171 * never the case.
172 */
173 return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
174 regs->ip == landing_pad &&
175 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
176#else
177 /*
178 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
179 *
180 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
181 * because the ECX fixup above will ensure that this is essentially
182 * never the case.
183 *
184 * We don't allow syscalls at all from VM86 mode, but we still
185 * need to check VM, because we might be returning from sys_vm86.
186 */
187 return static_cpu_has(X86_FEATURE_SEP) &&
188 regs->cs == __USER_CS && regs->ss == __USER_DS &&
189 regs->ip == landing_pad &&
190 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
191#endif
192}
193
194/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
195__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
196{
197 /* SYSENTER loses RSP, but the vDSO saved it in RBP. */
198 regs->sp = regs->bp;
199
200 /* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
201 regs->flags |= X86_EFLAGS_IF;
202
203 return do_fast_syscall_32(regs);
204}
205#endif
206
207SYSCALL_DEFINE0(ni_syscall)
208{
209 return -ENOSYS;
210}
211
212noinstr bool idtentry_enter_nmi(struct pt_regs *regs)
213{
214 bool irq_state = lockdep_hardirqs_enabled();
215
216 __nmi_enter();
217 lockdep_hardirqs_off(CALLER_ADDR0);
218 lockdep_hardirq_enter();
219 rcu_nmi_enter();
220
221 instrumentation_begin();
222 trace_hardirqs_off_finish();
223 ftrace_nmi_enter();
224 instrumentation_end();
225
226 return irq_state;
227}
228
229noinstr void idtentry_exit_nmi(struct pt_regs *regs, bool restore)
230{
231 instrumentation_begin();
232 ftrace_nmi_exit();
233 if (restore) {
234 trace_hardirqs_on_prepare();
235 lockdep_hardirqs_on_prepare(CALLER_ADDR0);
236 }
237 instrumentation_end();
238
239 rcu_nmi_exit();
240 lockdep_hardirq_exit();
241 if (restore)
242 lockdep_hardirqs_on(CALLER_ADDR0);
243 __nmi_exit();
244}
245
246#ifdef CONFIG_XEN_PV
247#ifndef CONFIG_PREEMPTION
248/*
249 * Some hypercalls issued by the toolstack can take many 10s of
250 * seconds. Allow tasks running hypercalls via the privcmd driver to
251 * be voluntarily preempted even if full kernel preemption is
252 * disabled.
253 *
254 * Such preemptible hypercalls are bracketed by
255 * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
256 * calls.
257 */
258DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
259EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
260
261/*
262 * In case of scheduling the flag must be cleared and restored after
263 * returning from schedule as the task might move to a different CPU.
264 */
265static __always_inline bool get_and_clear_inhcall(void)
266{
267 bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);
268
269 __this_cpu_write(xen_in_preemptible_hcall, false);
270 return inhcall;
271}
272
273static __always_inline void restore_inhcall(bool inhcall)
274{
275 __this_cpu_write(xen_in_preemptible_hcall, inhcall);
276}
277#else
278static __always_inline bool get_and_clear_inhcall(void) { return false; }
279static __always_inline void restore_inhcall(bool inhcall) { }
280#endif
281
282static void __xen_pv_evtchn_do_upcall(void)
283{
284 irq_enter_rcu();
285 inc_irq_stat(irq_hv_callback_count);
286
287 xen_hvm_evtchn_do_upcall();
288
289 irq_exit_rcu();
290}
291
292__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
293{
294 struct pt_regs *old_regs;
295 bool inhcall;
296 irqentry_state_t state;
297
298 state = irqentry_enter(regs);
299 old_regs = set_irq_regs(regs);
300
301 instrumentation_begin();
302 run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
303 instrumentation_begin();
304
305 set_irq_regs(old_regs);
306
307 inhcall = get_and_clear_inhcall();
308 if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
309 instrumentation_begin();
310 irqentry_exit_cond_resched();
311 instrumentation_end();
312 restore_inhcall(inhcall);
313 } else {
314 irqentry_exit(regs, state);
315 }
316}
317#endif /* CONFIG_XEN_PV */
1/*
2 * common.c - C code for kernel entry and exit
3 * Copyright (c) 2015 Andrew Lutomirski
4 * GPL v2
5 *
6 * Based on asm and ptrace code by many authors. The code here originated
7 * in ptrace.c and signal.c.
8 */
9
10#include <linux/kernel.h>
11#include <linux/sched.h>
12#include <linux/sched/task_stack.h>
13#include <linux/mm.h>
14#include <linux/smp.h>
15#include <linux/errno.h>
16#include <linux/ptrace.h>
17#include <linux/tracehook.h>
18#include <linux/audit.h>
19#include <linux/seccomp.h>
20#include <linux/signal.h>
21#include <linux/export.h>
22#include <linux/context_tracking.h>
23#include <linux/user-return-notifier.h>
24#include <linux/nospec.h>
25#include <linux/uprobes.h>
26#include <linux/livepatch.h>
27#include <linux/syscalls.h>
28
29#include <asm/desc.h>
30#include <asm/traps.h>
31#include <asm/vdso.h>
32#include <linux/uaccess.h>
33#include <asm/cpufeature.h>
34
35#define CREATE_TRACE_POINTS
36#include <trace/events/syscalls.h>
37
38#ifdef CONFIG_CONTEXT_TRACKING
39/* Called on entry from user mode with IRQs off. */
40__visible inline void enter_from_user_mode(void)
41{
42 CT_WARN_ON(ct_state() != CONTEXT_USER);
43 user_exit_irqoff();
44}
45#else
46static inline void enter_from_user_mode(void) {}
47#endif
48
49static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
50{
51#ifdef CONFIG_X86_64
52 if (arch == AUDIT_ARCH_X86_64) {
53 audit_syscall_entry(regs->orig_ax, regs->di,
54 regs->si, regs->dx, regs->r10);
55 } else
56#endif
57 {
58 audit_syscall_entry(regs->orig_ax, regs->bx,
59 regs->cx, regs->dx, regs->si);
60 }
61}
62
63/*
64 * Returns the syscall nr to run (which should match regs->orig_ax) or -1
65 * to skip the syscall.
66 */
67static long syscall_trace_enter(struct pt_regs *regs)
68{
69 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
70
71 struct thread_info *ti = current_thread_info();
72 unsigned long ret = 0;
73 bool emulated = false;
74 u32 work;
75
76 if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
77 BUG_ON(regs != task_pt_regs(current));
78
79 work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
80
81 if (unlikely(work & _TIF_SYSCALL_EMU))
82 emulated = true;
83
84 if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
85 tracehook_report_syscall_entry(regs))
86 return -1L;
87
88 if (emulated)
89 return -1L;
90
91#ifdef CONFIG_SECCOMP
92 /*
93 * Do seccomp after ptrace, to catch any tracer changes.
94 */
95 if (work & _TIF_SECCOMP) {
96 struct seccomp_data sd;
97
98 sd.arch = arch;
99 sd.nr = regs->orig_ax;
100 sd.instruction_pointer = regs->ip;
101#ifdef CONFIG_X86_64
102 if (arch == AUDIT_ARCH_X86_64) {
103 sd.args[0] = regs->di;
104 sd.args[1] = regs->si;
105 sd.args[2] = regs->dx;
106 sd.args[3] = regs->r10;
107 sd.args[4] = regs->r8;
108 sd.args[5] = regs->r9;
109 } else
110#endif
111 {
112 sd.args[0] = regs->bx;
113 sd.args[1] = regs->cx;
114 sd.args[2] = regs->dx;
115 sd.args[3] = regs->si;
116 sd.args[4] = regs->di;
117 sd.args[5] = regs->bp;
118 }
119
120 ret = __secure_computing(&sd);
121 if (ret == -1)
122 return ret;
123 }
124#endif
125
126 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
127 trace_sys_enter(regs, regs->orig_ax);
128
129 do_audit_syscall_entry(regs, arch);
130
131 return ret ?: regs->orig_ax;
132}
133
134#define EXIT_TO_USERMODE_LOOP_FLAGS \
135 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
136 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
137
138static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
139{
140 /*
141 * In order to return to user mode, we need to have IRQs off with
142 * none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags
143 * can be set at any time on preemptable kernels if we have IRQs on,
144 * so we need to loop. Disabling preemption wouldn't help: doing the
145 * work to clear some of the flags can sleep.
146 */
147 while (true) {
148 /* We have work to do. */
149 local_irq_enable();
150
151 if (cached_flags & _TIF_NEED_RESCHED)
152 schedule();
153
154 if (cached_flags & _TIF_UPROBE)
155 uprobe_notify_resume(regs);
156
157 if (cached_flags & _TIF_PATCH_PENDING)
158 klp_update_patch_state(current);
159
160 /* deal with pending signal delivery */
161 if (cached_flags & _TIF_SIGPENDING)
162 do_signal(regs);
163
164 if (cached_flags & _TIF_NOTIFY_RESUME) {
165 clear_thread_flag(TIF_NOTIFY_RESUME);
166 tracehook_notify_resume(regs);
167 }
168
169 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
170 fire_user_return_notifiers();
171
172 /* Disable IRQs and retry */
173 local_irq_disable();
174
175 cached_flags = READ_ONCE(current_thread_info()->flags);
176
177 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
178 break;
179 }
180}
181
182/* Called with IRQs disabled. */
183__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
184{
185 struct thread_info *ti = current_thread_info();
186 u32 cached_flags;
187
188 addr_limit_user_check();
189
190 lockdep_assert_irqs_disabled();
191 lockdep_sys_exit();
192
193 cached_flags = READ_ONCE(ti->flags);
194
195 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
196 exit_to_usermode_loop(regs, cached_flags);
197
198#ifdef CONFIG_COMPAT
199 /*
200 * Compat syscalls set TS_COMPAT. Make sure we clear it before
201 * returning to user mode. We need to clear it *after* signal
202 * handling, because syscall restart has a fixup for compat
203 * syscalls. The fixup is exercised by the ptrace_syscall_32
204 * selftest.
205 *
206 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
207 * special case only applies after poking regs and before the
208 * very next return to user mode.
209 */
210 ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
211#endif
212
213 user_enter_irqoff();
214}
215
216#define SYSCALL_EXIT_WORK_FLAGS \
217 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
218 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
219
220static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
221{
222 bool step;
223
224 audit_syscall_exit(regs);
225
226 if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
227 trace_sys_exit(regs, regs->ax);
228
229 /*
230 * If TIF_SYSCALL_EMU is set, we only get here because of
231 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
232 * We already reported this syscall instruction in
233 * syscall_trace_enter().
234 */
235 step = unlikely(
236 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
237 == _TIF_SINGLESTEP);
238 if (step || cached_flags & _TIF_SYSCALL_TRACE)
239 tracehook_report_syscall_exit(regs, step);
240}
241
242/*
243 * Called with IRQs on and fully valid regs. Returns with IRQs off in a
244 * state such that we can immediately switch to user mode.
245 */
246__visible inline void syscall_return_slowpath(struct pt_regs *regs)
247{
248 struct thread_info *ti = current_thread_info();
249 u32 cached_flags = READ_ONCE(ti->flags);
250
251 CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
252
253 if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
254 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
255 local_irq_enable();
256
257 /*
258 * First do one-time work. If these work items are enabled, we
259 * want to run them exactly once per syscall exit with IRQs on.
260 */
261 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
262 syscall_slow_exit_work(regs, cached_flags);
263
264 local_irq_disable();
265 prepare_exit_to_usermode(regs);
266}
267
268#ifdef CONFIG_X86_64
269__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
270{
271 struct thread_info *ti;
272
273 enter_from_user_mode();
274 local_irq_enable();
275 ti = current_thread_info();
276 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
277 nr = syscall_trace_enter(regs);
278
279 /*
280 * NB: Native and x32 syscalls are dispatched from the same
281 * table. The only functional difference is the x32 bit in
282 * regs->orig_ax, which changes the behavior of some syscalls.
283 */
284 nr &= __SYSCALL_MASK;
285 if (likely(nr < NR_syscalls)) {
286 nr = array_index_nospec(nr, NR_syscalls);
287 regs->ax = sys_call_table[nr](regs);
288 }
289
290 syscall_return_slowpath(regs);
291}
292#endif
293
294#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
295/*
296 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
297 * all entry and exit work and returns with IRQs off. This function is
298 * extremely hot in workloads that use it, and it's usually called from
299 * do_fast_syscall_32, so forcibly inline it to improve performance.
300 */
301static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
302{
303 struct thread_info *ti = current_thread_info();
304 unsigned int nr = (unsigned int)regs->orig_ax;
305
306#ifdef CONFIG_IA32_EMULATION
307 ti->status |= TS_COMPAT;
308#endif
309
310 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
311 /*
312 * Subtlety here: if ptrace pokes something larger than
313 * 2^32-1 into orig_ax, this truncates it. This may or
314 * may not be necessary, but it matches the old asm
315 * behavior.
316 */
317 nr = syscall_trace_enter(regs);
318 }
319
320 if (likely(nr < IA32_NR_syscalls)) {
321 nr = array_index_nospec(nr, IA32_NR_syscalls);
322#ifdef CONFIG_IA32_EMULATION
323 regs->ax = ia32_sys_call_table[nr](regs);
324#else
325 /*
326 * It's possible that a 32-bit syscall implementation
327 * takes a 64-bit parameter but nonetheless assumes that
328 * the high bits are zero. Make sure we zero-extend all
329 * of the args.
330 */
331 regs->ax = ia32_sys_call_table[nr](
332 (unsigned int)regs->bx, (unsigned int)regs->cx,
333 (unsigned int)regs->dx, (unsigned int)regs->si,
334 (unsigned int)regs->di, (unsigned int)regs->bp);
335#endif /* CONFIG_IA32_EMULATION */
336 }
337
338 syscall_return_slowpath(regs);
339}
340
341/* Handles int $0x80 */
342__visible void do_int80_syscall_32(struct pt_regs *regs)
343{
344 enter_from_user_mode();
345 local_irq_enable();
346 do_syscall_32_irqs_on(regs);
347}
348
349/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
350__visible long do_fast_syscall_32(struct pt_regs *regs)
351{
352 /*
353 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
354 * convention. Adjust regs so it looks like we entered using int80.
355 */
356
357 unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
358 vdso_image_32.sym_int80_landing_pad;
359
360 /*
361 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
362 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
363 * Fix it up.
364 */
365 regs->ip = landing_pad;
366
367 enter_from_user_mode();
368
369 local_irq_enable();
370
371 /* Fetch EBP from where the vDSO stashed it. */
372 if (
373#ifdef CONFIG_X86_64
374 /*
375 * Micro-optimization: the pointer we're following is explicitly
376 * 32 bits, so it can't be out of range.
377 */
378 __get_user(*(u32 *)®s->bp,
379 (u32 __user __force *)(unsigned long)(u32)regs->sp)
380#else
381 get_user(*(u32 *)®s->bp,
382 (u32 __user __force *)(unsigned long)(u32)regs->sp)
383#endif
384 ) {
385
386 /* User code screwed up. */
387 local_irq_disable();
388 regs->ax = -EFAULT;
389 prepare_exit_to_usermode(regs);
390 return 0; /* Keep it simple: use IRET. */
391 }
392
393 /* Now this is just like a normal syscall. */
394 do_syscall_32_irqs_on(regs);
395
396#ifdef CONFIG_X86_64
397 /*
398 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
399 * SYSRETL is available on all 64-bit CPUs, so we don't need to
400 * bother with SYSEXIT.
401 *
402 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
403 * because the ECX fixup above will ensure that this is essentially
404 * never the case.
405 */
406 return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
407 regs->ip == landing_pad &&
408 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
409#else
410 /*
411 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
412 *
413 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
414 * because the ECX fixup above will ensure that this is essentially
415 * never the case.
416 *
417 * We don't allow syscalls at all from VM86 mode, but we still
418 * need to check VM, because we might be returning from sys_vm86.
419 */
420 return static_cpu_has(X86_FEATURE_SEP) &&
421 regs->cs == __USER_CS && regs->ss == __USER_DS &&
422 regs->ip == landing_pad &&
423 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
424#endif
425}
426#endif