sdei.c
// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2017 Arm Ltd.
#define pr_fmt(fmt) "sdei: " fmt
#include <linux/arm_sdei.h>
#include <linux/hardirq.h>
#include <linux/irqflags.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>
#include <asm/alternative.h>
#include <asm/kprobes.h>
#include <asm/mmu.h>
#include <asm/ptrace.h>
#include <asm/sections.h>
#include <asm/stacktrace.h>
#include <asm/sysreg.h>
#include <asm/vmap_stack.h>
unsigned long sdei_exit_mode;
/*
* VMAP'd stacks checking for stack overflow on exception using sp as a scratch
* register, meaning SDEI has to switch to its own stack. We need two stacks as
* a critical event may interrupt a normal event that has just taken a
* synchronous exception, and is using sp as scratch register. For a critical
* event interrupting a normal event, we can't reliably tell if we were on the
* sdei stack.
* For now, we allocate stacks when the driver is probed.
*/
DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
#ifdef CONFIG_VMAP_STACK
DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
#endif
static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
{
unsigned long *p;
p = per_cpu(*ptr, cpu);
if (p) {
per_cpu(*ptr, cpu) = NULL;
vfree(p);
}
}
static void free_sdei_stacks(void)
{
int cpu;
for_each_possible_cpu(cpu) {
_free_sdei_stack(&sdei_stack_normal_ptr, cpu);
_free_sdei_stack(&sdei_stack_critical_ptr, cpu);
}
}
static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
{
unsigned long *p;
p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
if (!p)
return -ENOMEM;
per_cpu(*ptr, cpu) = p;
return 0;
}
static int init_sdei_stacks(void)
{
int cpu;
int err = 0;
for_each_possible_cpu(cpu) {
err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
if (err)
break;
err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
if (err)
break;
}
if (err)
free_sdei_stacks();
return err;
}
static bool on_sdei_normal_stack(unsigned long sp, struct stack_info *info)
{
unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr);
unsigned long high = low + SDEI_STACK_SIZE;
if (sp < low || sp >= high)
return false;
if (info) {
info->low = low;
info->high = high;
info->type = STACK_TYPE_SDEI_NORMAL;
}
return true;
}
static bool on_sdei_critical_stack(unsigned long sp, struct stack_info *info)
{
unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr);
unsigned long high = low + SDEI_STACK_SIZE;
if (sp < low || sp >= high)
return false;
if (info) {
info->low = low;
info->high = high;
info->type = STACK_TYPE_SDEI_CRITICAL;
}
return true;
}
bool _on_sdei_stack(unsigned long sp, struct stack_info *info)
{
if (!IS_ENABLED(CONFIG_VMAP_STACK))
return false;
if (on_sdei_critical_stack(sp, info))
return true;
if (on_sdei_normal_stack(sp, info))
return true;
return false;
}
unsigned long sdei_arch_get_entry_point(int conduit)
{
/*
* SDEI works between adjacent exception levels. If we booted at EL1 we
* assume a hypervisor is marshalling events. If we booted at EL2 and
* dropped to EL1 because we don't support VHE, then we can't support
* SDEI.
*/
if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) {
pr_err("Not supported on this hardware/boot configuration\n");
return 0;
}
if (IS_ENABLED(CONFIG_VMAP_STACK)) {
if (init_sdei_stacks())
return 0;
}
sdei_exit_mode = (conduit == CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
if (arm64_kernel_unmapped_at_el0()) {
unsigned long offset;
offset = (unsigned long)__sdei_asm_entry_trampoline -
(unsigned long)__entry_tramp_text_start;
return TRAMP_VALIAS + offset;
} else
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
return (unsigned long)__sdei_asm_handler;
}
/*
* __sdei_handler() returns one of:
* SDEI_EV_HANDLED - success, return to the interrupted context.
* SDEI_EV_FAILED - failure, return this error code to firmare.
* virtual-address - success, return to this address.
*/
static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
struct sdei_registered_event *arg)
{
u32 mode;
int i, err = 0;
int clobbered_registers = 4;
u64 elr = read_sysreg(elr_el1);
u32 kernel_mode = read_sysreg(CurrentEL) | 1; /* +SPSel */
unsigned long vbar = read_sysreg(vbar_el1);
if (arm64_kernel_unmapped_at_el0())
clobbered_registers++;
/* Retrieve the missing registers values */
for (i = 0; i < clobbered_registers; i++) {
/* from within the handler, this call always succeeds */
sdei_api_event_context(i, ®s->regs[i]);
}
/*
* We didn't take an exception to get here, set PAN. UAO will be cleared
* by sdei_event_handler()s set_fs(USER_DS) call.
*/
__uaccess_enable_hw_pan();
err = sdei_event_handler(regs, arg);
if (err)
return SDEI_EV_FAILED;
if (elr != read_sysreg(elr_el1)) {
/*
* We took a synchronous exception from the SDEI handler.
* This could deadlock, and if you interrupt KVM it will
* hyp-panic instead.
*/
pr_warn("unsafe: exception during handler\n");
}
mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);
/*
* If we interrupted the kernel with interrupts masked, we always go
* back to wherever we came from.
*/
if (mode == kernel_mode && !interrupts_enabled(regs))
return SDEI_EV_HANDLED;
/*
* Otherwise, we pretend this was an IRQ. This lets user space tasks
* receive signals before we return to them, and KVM to invoke it's
* world switch to do the same.
*
* See DDI0487B.a Table D1-7 'Vector offsets from vector table base
* address'.
*/
if (mode == kernel_mode)
return vbar + 0x280;
else if (mode & PSR_MODE32_BIT)
return vbar + 0x680;
return vbar + 0x480;
}
asmlinkage __kprobes notrace unsigned long
__sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
{
unsigned long ret;
bool do_nmi_exit = false;
/*
* nmi_enter() deals with printk() re-entrance and use of RCU when
* RCU believed this CPU was idle. Because critical events can
* interrupt normal events, we may already be in_nmi().
*/
if (!in_nmi()) {
nmi_enter();
do_nmi_exit = true;
}
ret = _sdei_handler(regs, arg);
if (do_nmi_exit)
nmi_exit();
return ret;
}
