1// SPDX-License-Identifier: GPL-2.0
  2// Copyright (C) 2017 Arm Ltd.
  3#define pr_fmt(fmt) "sdei: " fmt
  4
  5#include <linux/arm-smccc.h>
  6#include <linux/arm_sdei.h>
  7#include <linux/hardirq.h>
  8#include <linux/irqflags.h>
  9#include <linux/sched/task_stack.h>
 10#include <linux/scs.h>
 11#include <linux/uaccess.h>
 12
 13#include <asm/alternative.h>
 14#include <asm/exception.h>
 15#include <asm/kprobes.h>
 16#include <asm/mmu.h>
 17#include <asm/ptrace.h>
 18#include <asm/sections.h>
 19#include <asm/stacktrace.h>
 20#include <asm/sysreg.h>
 21#include <asm/vmap_stack.h>
 22
 23unsigned long sdei_exit_mode;
 24
 25/*
 26 * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
 27 * register, meaning SDEI has to switch to its own stack. We need two stacks as
 28 * a critical event may interrupt a normal event that has just taken a
 29 * synchronous exception, and is using sp as scratch register. For a critical
 30 * event interrupting a normal event, we can't reliably tell if we were on the
 31 * sdei stack.
 32 * For now, we allocate stacks when the driver is probed.
 33 */
 34DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
 35DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
 36
 37#ifdef CONFIG_VMAP_STACK
 38DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
 39DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
 40#endif
 41
 42DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
 43DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
 44
 45#ifdef CONFIG_SHADOW_CALL_STACK
 46DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
 47DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
 48#endif
 49
 50DEFINE_PER_CPU(struct sdei_registered_event *, sdei_active_normal_event);
 51DEFINE_PER_CPU(struct sdei_registered_event *, sdei_active_critical_event);
 52
 53static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
 54{
 55	unsigned long *p;
 56
 57	p = per_cpu(*ptr, cpu);
 58	if (p) {
 59		per_cpu(*ptr, cpu) = NULL;
 60		vfree(p);
 61	}
 62}
 63
 64static void free_sdei_stacks(void)
 65{
 66	int cpu;
 67
 68	if (!IS_ENABLED(CONFIG_VMAP_STACK))
 69		return;
 70
 71	for_each_possible_cpu(cpu) {
 72		_free_sdei_stack(&sdei_stack_normal_ptr, cpu);
 73		_free_sdei_stack(&sdei_stack_critical_ptr, cpu);
 74	}
 75}
 76
 77static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
 78{
 79	unsigned long *p;
 80
 81	p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
 82	if (!p)
 83		return -ENOMEM;
 84	per_cpu(*ptr, cpu) = p;
 85
 86	return 0;
 87}
 88
 89static int init_sdei_stacks(void)
 90{
 91	int cpu;
 92	int err = 0;
 93
 94	if (!IS_ENABLED(CONFIG_VMAP_STACK))
 95		return 0;
 96
 97	for_each_possible_cpu(cpu) {
 98		err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
 99		if (err)
100			break;
101		err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
102		if (err)
103			break;
104	}
105
106	if (err)
107		free_sdei_stacks();
108
109	return err;
110}
111
112static void _free_sdei_scs(unsigned long * __percpu *ptr, int cpu)
113{
114	void *s;
115
116	s = per_cpu(*ptr, cpu);
117	if (s) {
118		per_cpu(*ptr, cpu) = NULL;
119		scs_free(s);
120	}
121}
122
123static void free_sdei_scs(void)
124{
125	int cpu;
126
127	for_each_possible_cpu(cpu) {
128		_free_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
129		_free_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
130	}
131}
132
133static int _init_sdei_scs(unsigned long * __percpu *ptr, int cpu)
134{
135	void *s;
136
137	s = scs_alloc(cpu_to_node(cpu));
138	if (!s)
139		return -ENOMEM;
140	per_cpu(*ptr, cpu) = s;
141
142	return 0;
143}
144
145static int init_sdei_scs(void)
146{
147	int cpu;
148	int err = 0;
149
150	if (!scs_is_enabled())
151		return 0;
152
153	for_each_possible_cpu(cpu) {
154		err = _init_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
155		if (err)
156			break;
157		err = _init_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
158		if (err)
159			break;
160	}
161
162	if (err)
163		free_sdei_scs();
164
165	return err;
166}
167
168unsigned long sdei_arch_get_entry_point(int conduit)
169{
170	/*
171	 * SDEI works between adjacent exception levels. If we booted at EL1 we
172	 * assume a hypervisor is marshalling events. If we booted at EL2 and
173	 * dropped to EL1 because we don't support VHE, then we can't support
174	 * SDEI.
175	 */
176	if (is_hyp_nvhe()) {
177		pr_err("Not supported on this hardware/boot configuration\n");
178		goto out_err;
179	}
180
181	if (init_sdei_stacks())
182		goto out_err;
183
184	if (init_sdei_scs())
185		goto out_err_free_stacks;
186
187	sdei_exit_mode = (conduit == SMCCC_CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
188
189#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
190	if (arm64_kernel_unmapped_at_el0()) {
191		unsigned long offset;
192
193		offset = (unsigned long)__sdei_asm_entry_trampoline -
194			 (unsigned long)__entry_tramp_text_start;
195		return TRAMP_VALIAS + offset;
196	} else
197#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
198		return (unsigned long)__sdei_asm_handler;
199
200out_err_free_stacks:
201	free_sdei_stacks();
202out_err:
203	return 0;
204}
205
206/*
207 * do_sdei_event() returns one of:
208 *  SDEI_EV_HANDLED -  success, return to the interrupted context.
209 *  SDEI_EV_FAILED  -  failure, return this error code to firmare.
210 *  virtual-address -  success, return to this address.
211 */
212unsigned long __kprobes do_sdei_event(struct pt_regs *regs,
213				      struct sdei_registered_event *arg)
214{
215	u32 mode;
216	int i, err = 0;
217	int clobbered_registers = 4;
218	u64 elr = read_sysreg(elr_el1);
219	u32 kernel_mode = read_sysreg(CurrentEL) | 1;	/* +SPSel */
220	unsigned long vbar = read_sysreg(vbar_el1);
221
222	if (arm64_kernel_unmapped_at_el0())
223		clobbered_registers++;
224
225	/* Retrieve the missing registers values */
226	for (i = 0; i < clobbered_registers; i++) {
227		/* from within the handler, this call always succeeds */
228		sdei_api_event_context(i, &regs->regs[i]);
229	}
230
231	err = sdei_event_handler(regs, arg);
232	if (err)
233		return SDEI_EV_FAILED;
234
235	if (elr != read_sysreg(elr_el1)) {
236		/*
237		 * We took a synchronous exception from the SDEI handler.
238		 * This could deadlock, and if you interrupt KVM it will
239		 * hyp-panic instead.
240		 */
241		pr_warn("unsafe: exception during handler\n");
242	}
243
244	mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
245
246	/*
247	 * If we interrupted the kernel with interrupts masked, we always go
248	 * back to wherever we came from.
249	 */
250	if (mode == kernel_mode && !interrupts_enabled(regs))
251		return SDEI_EV_HANDLED;
252
253	/*
254	 * Otherwise, we pretend this was an IRQ. This lets user space tasks
255	 * receive signals before we return to them, and KVM to invoke it's
256	 * world switch to do the same.
257	 *
258	 * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
259	 * address'.
260	 */
261	if (mode == kernel_mode)
262		return vbar + 0x280;
263	else if (mode & PSR_MODE32_BIT)
264		return vbar + 0x680;
265
266	return vbar + 0x480;
267}