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