sdei.c

  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
 37DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
 38DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
 39
 40DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
 41DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
 42
 43#ifdef CONFIG_SHADOW_CALL_STACK
 44DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr);
 45DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr);
 46#endif
 47
 48DEFINE_PER_CPU(struct sdei_registered_event *, sdei_active_normal_event);
 49DEFINE_PER_CPU(struct sdei_registered_event *, sdei_active_critical_event);
 50
 51static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
 52{
 53	unsigned long *p;
 54
 55	p = per_cpu(*ptr, cpu);
 56	if (p) {
 57		per_cpu(*ptr, cpu) = NULL;
 58		vfree(p);
 59	}
 60}
 61
 62static void free_sdei_stacks(void)
 63{
 64	int cpu;
 65
 66	for_each_possible_cpu(cpu) {
 67		_free_sdei_stack(&sdei_stack_normal_ptr, cpu);
 68		_free_sdei_stack(&sdei_stack_critical_ptr, cpu);
 69	}
 70}
 71
 72static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
 73{
 74	unsigned long *p;
 75
 76	p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
 77	if (!p)
 78		return -ENOMEM;
 79	per_cpu(*ptr, cpu) = p;
 80
 81	return 0;
 82}
 83
 84static int init_sdei_stacks(void)
 85{
 86	int cpu;
 87	int err = 0;
 88
 89	for_each_possible_cpu(cpu) {
 90		err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
 91		if (err)
 92			break;
 93		err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
 94		if (err)
 95			break;
 96	}
 97
 98	if (err)
 99		free_sdei_stacks();
100
101	return err;
102}
103
104static void _free_sdei_scs(unsigned long * __percpu *ptr, int cpu)
105{
106	void *s;
107
108	s = per_cpu(*ptr, cpu);
109	if (s) {
110		per_cpu(*ptr, cpu) = NULL;
111		scs_free(s);
112	}
113}
114
115static void free_sdei_scs(void)
116{
117	int cpu;
118
119	for_each_possible_cpu(cpu) {
120		_free_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
121		_free_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
122	}
123}
124
125static int _init_sdei_scs(unsigned long * __percpu *ptr, int cpu)
126{
127	void *s;
128
129	s = scs_alloc(cpu_to_node(cpu));
130	if (!s)
131		return -ENOMEM;
132	per_cpu(*ptr, cpu) = s;
133
134	return 0;
135}
136
137static int init_sdei_scs(void)
138{
139	int cpu;
140	int err = 0;
141
142	if (!scs_is_enabled())
143		return 0;
144
145	for_each_possible_cpu(cpu) {
146		err = _init_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
147		if (err)
148			break;
149		err = _init_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
150		if (err)
151			break;
152	}
153
154	if (err)
155		free_sdei_scs();
156
157	return err;
158}
159
160unsigned long sdei_arch_get_entry_point(int conduit)
161{
162	/*
163	 * SDEI works between adjacent exception levels. If we booted at EL1 we
164	 * assume a hypervisor is marshalling events. If we booted at EL2 and
165	 * dropped to EL1 because we don't support VHE, then we can't support
166	 * SDEI.
167	 */
168	if (is_hyp_nvhe()) {
169		pr_err("Not supported on this hardware/boot configuration\n");
170		goto out_err;
171	}
172
173	if (init_sdei_stacks())
174		goto out_err;
175
176	if (init_sdei_scs())
177		goto out_err_free_stacks;
178
179	sdei_exit_mode = (conduit == SMCCC_CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
180
181#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
182	if (arm64_kernel_unmapped_at_el0()) {
183		unsigned long offset;
184
185		offset = (unsigned long)__sdei_asm_entry_trampoline -
186			 (unsigned long)__entry_tramp_text_start;
187		return TRAMP_VALIAS + offset;
188	} else
189#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
190		return (unsigned long)__sdei_asm_handler;
191
192out_err_free_stacks:
193	free_sdei_stacks();
194out_err:
195	return 0;
196}
197
198/*
199 * do_sdei_event() returns one of:
200 *  SDEI_EV_HANDLED -  success, return to the interrupted context.
201 *  SDEI_EV_FAILED  -  failure, return this error code to firmware.
202 *  virtual-address -  success, return to this address.
203 */
204unsigned long __kprobes do_sdei_event(struct pt_regs *regs,
205				      struct sdei_registered_event *arg)
206{
207	u32 mode;
208	int i, err = 0;
209	int clobbered_registers = 4;
210	u64 elr = read_sysreg(elr_el1);
211	u32 kernel_mode = read_sysreg(CurrentEL) | 1;	/* +SPSel */
212	unsigned long vbar = read_sysreg(vbar_el1);
213
214	if (arm64_kernel_unmapped_at_el0())
215		clobbered_registers++;
216
217	/* Retrieve the missing registers values */
218	for (i = 0; i < clobbered_registers; i++) {
219		/* from within the handler, this call always succeeds */
220		sdei_api_event_context(i, &regs->regs[i]);
221	}
222
223	err = sdei_event_handler(regs, arg);
224	if (err)
225		return SDEI_EV_FAILED;
226
227	if (elr != read_sysreg(elr_el1)) {
228		/*
229		 * We took a synchronous exception from the SDEI handler.
230		 * This could deadlock, and if you interrupt KVM it will
231		 * hyp-panic instead.
232		 */
233		pr_warn("unsafe: exception during handler\n");
234	}
235
236	mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
237
238	/*
239	 * If we interrupted the kernel with interrupts masked, we always go
240	 * back to wherever we came from.
241	 */
242	if (mode == kernel_mode && regs_irqs_disabled(regs))
243		return SDEI_EV_HANDLED;
244
245	/*
246	 * Otherwise, we pretend this was an IRQ. This lets user space tasks
247	 * receive signals before we return to them, and KVM to invoke it's
248	 * world switch to do the same.
249	 *
250	 * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
251	 * address'.
252	 */
253	if (mode == kernel_mode)
254		return vbar + 0x280;
255	else if (mode & PSR_MODE32_BIT)
256		return vbar + 0x680;
257
258	return vbar + 0x480;
259}