xref: /openbmc/linux/arch/x86/entry/common.c (revision d58f75de)
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 	add_random_kstack_offset();
42 	nr = syscall_enter_from_user_mode(regs, nr);
43 
44 	instrumentation_begin();
45 	if (likely(nr < NR_syscalls)) {
46 		nr = array_index_nospec(nr, NR_syscalls);
47 		regs->ax = sys_call_table[nr](regs);
48 #ifdef CONFIG_X86_X32_ABI
49 	} else if (likely((nr & __X32_SYSCALL_BIT) &&
50 			  (nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
51 		nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
52 					X32_NR_syscalls);
53 		regs->ax = x32_sys_call_table[nr](regs);
54 #endif
55 	}
56 	instrumentation_end();
57 	syscall_exit_to_user_mode(regs);
58 }
59 #endif
60 
61 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
62 static __always_inline unsigned int syscall_32_enter(struct pt_regs *regs)
63 {
64 	if (IS_ENABLED(CONFIG_IA32_EMULATION))
65 		current_thread_info()->status |= TS_COMPAT;
66 
67 	return (unsigned int)regs->orig_ax;
68 }
69 
70 /*
71  * Invoke a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.
72  */
73 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs,
74 						  unsigned int nr)
75 {
76 	if (likely(nr < IA32_NR_syscalls)) {
77 		nr = array_index_nospec(nr, IA32_NR_syscalls);
78 		regs->ax = ia32_sys_call_table[nr](regs);
79 	}
80 }
81 
82 /* Handles int $0x80 */
83 __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
84 {
85 	unsigned int nr = syscall_32_enter(regs);
86 
87 	add_random_kstack_offset();
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 	instrumentation_begin();
95 
96 	do_syscall_32_irqs_on(regs, nr);
97 
98 	instrumentation_end();
99 	syscall_exit_to_user_mode(regs);
100 }
101 
102 static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
103 {
104 	unsigned int nr = syscall_32_enter(regs);
105 	int res;
106 
107 	add_random_kstack_offset();
108 	/*
109 	 * This cannot use syscall_enter_from_user_mode() as it has to
110 	 * fetch EBP before invoking any of the syscall entry work
111 	 * functions.
112 	 */
113 	syscall_enter_from_user_mode_prepare(regs);
114 
115 	instrumentation_begin();
116 	/* Fetch EBP from where the vDSO stashed it. */
117 	if (IS_ENABLED(CONFIG_X86_64)) {
118 		/*
119 		 * Micro-optimization: the pointer we're following is
120 		 * explicitly 32 bits, so it can't be out of range.
121 		 */
122 		res = __get_user(*(u32 *)&regs->bp,
123 			 (u32 __user __force *)(unsigned long)(u32)regs->sp);
124 	} else {
125 		res = get_user(*(u32 *)&regs->bp,
126 		       (u32 __user __force *)(unsigned long)(u32)regs->sp);
127 	}
128 
129 	if (res) {
130 		/* User code screwed up. */
131 		regs->ax = -EFAULT;
132 
133 		instrumentation_end();
134 		local_irq_disable();
135 		irqentry_exit_to_user_mode(regs);
136 		return false;
137 	}
138 
139 	/* The case truncates any ptrace induced syscall nr > 2^32 -1 */
140 	nr = (unsigned int)syscall_enter_from_user_mode_work(regs, nr);
141 
142 	/* Now this is just like a normal syscall. */
143 	do_syscall_32_irqs_on(regs, nr);
144 
145 	instrumentation_end();
146 	syscall_exit_to_user_mode(regs);
147 	return true;
148 }
149 
150 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
151 __visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
152 {
153 	/*
154 	 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
155 	 * convention.  Adjust regs so it looks like we entered using int80.
156 	 */
157 	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
158 					vdso_image_32.sym_int80_landing_pad;
159 
160 	/*
161 	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
162 	 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
163 	 * Fix it up.
164 	 */
165 	regs->ip = landing_pad;
166 
167 	/* Invoke the syscall. If it failed, keep it simple: use IRET. */
168 	if (!__do_fast_syscall_32(regs))
169 		return 0;
170 
171 #ifdef CONFIG_X86_64
172 	/*
173 	 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
174 	 * SYSRETL is available on all 64-bit CPUs, so we don't need to
175 	 * bother with SYSEXIT.
176 	 *
177 	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
178 	 * because the ECX fixup above will ensure that this is essentially
179 	 * never the case.
180 	 */
181 	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
182 		regs->ip == landing_pad &&
183 		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
184 #else
185 	/*
186 	 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
187 	 *
188 	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
189 	 * because the ECX fixup above will ensure that this is essentially
190 	 * never the case.
191 	 *
192 	 * We don't allow syscalls at all from VM86 mode, but we still
193 	 * need to check VM, because we might be returning from sys_vm86.
194 	 */
195 	return static_cpu_has(X86_FEATURE_SEP) &&
196 		regs->cs == __USER_CS && regs->ss == __USER_DS &&
197 		regs->ip == landing_pad &&
198 		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
199 #endif
200 }
201 
202 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
203 __visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
204 {
205 	/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
206 	regs->sp = regs->bp;
207 
208 	/* SYSENTER clobbers EFLAGS.IF.  Assume it was set in usermode. */
209 	regs->flags |= X86_EFLAGS_IF;
210 
211 	return do_fast_syscall_32(regs);
212 }
213 #endif
214 
215 SYSCALL_DEFINE0(ni_syscall)
216 {
217 	return -ENOSYS;
218 }
219 
220 #ifdef CONFIG_XEN_PV
221 #ifndef CONFIG_PREEMPTION
222 /*
223  * Some hypercalls issued by the toolstack can take many 10s of
224  * seconds. Allow tasks running hypercalls via the privcmd driver to
225  * be voluntarily preempted even if full kernel preemption is
226  * disabled.
227  *
228  * Such preemptible hypercalls are bracketed by
229  * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
230  * calls.
231  */
232 DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
233 EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
234 
235 /*
236  * In case of scheduling the flag must be cleared and restored after
237  * returning from schedule as the task might move to a different CPU.
238  */
239 static __always_inline bool get_and_clear_inhcall(void)
240 {
241 	bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);
242 
243 	__this_cpu_write(xen_in_preemptible_hcall, false);
244 	return inhcall;
245 }
246 
247 static __always_inline void restore_inhcall(bool inhcall)
248 {
249 	__this_cpu_write(xen_in_preemptible_hcall, inhcall);
250 }
251 #else
252 static __always_inline bool get_and_clear_inhcall(void) { return false; }
253 static __always_inline void restore_inhcall(bool inhcall) { }
254 #endif
255 
256 static void __xen_pv_evtchn_do_upcall(struct pt_regs *regs)
257 {
258 	struct pt_regs *old_regs = set_irq_regs(regs);
259 
260 	inc_irq_stat(irq_hv_callback_count);
261 
262 	xen_hvm_evtchn_do_upcall();
263 
264 	set_irq_regs(old_regs);
265 }
266 
267 __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
268 {
269 	irqentry_state_t state = irqentry_enter(regs);
270 	bool inhcall;
271 
272 	run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
273 
274 	inhcall = get_and_clear_inhcall();
275 	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
276 		instrumentation_begin();
277 		irqentry_exit_cond_resched();
278 		instrumentation_end();
279 		restore_inhcall(inhcall);
280 	} else {
281 		irqentry_exit(regs, state);
282 	}
283 }
284 #endif /* CONFIG_XEN_PV */
285