arch/arm64/kvm/stacktrace.c

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * KVM nVHE hypervisor stack tracing support.
 *
 * The unwinder implementation depends on the nVHE mode:
 *
 *   1) Non-protected nVHE mode - the host can directly access the
 *      HYP stack pages and unwind the HYP stack in EL1. This saves having
 *      to allocate shared buffers for the host to read the unwinded
 *      stacktrace.
 *
 *   2) pKVM (protected nVHE) mode - the host cannot directly access
 *      the HYP memory. The stack is unwinded in EL2 and dumped to a shared
 *      buffer where the host can read and print the stacktrace.
 *
 * Copyright (C) 2022 Google LLC
 */

#include <linux/kvm.h>
#include <linux/kvm_host.h>

#include <asm/kvm_mmu.h>
#include <asm/stacktrace/nvhe.h>

static struct stack_info stackinfo_get_overflow(void)
{
	struct kvm_nvhe_stacktrace_info *stacktrace_info
				= this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
	unsigned long low = (unsigned long)stacktrace_info->overflow_stack_base;
	unsigned long high = low + OVERFLOW_STACK_SIZE;

	return (struct stack_info) {
		.low = low,
		.high = high,
	};
}

static struct stack_info stackinfo_get_overflow_kern_va(void)
{
	unsigned long low = (unsigned long)this_cpu_ptr_nvhe_sym(overflow_stack);
	unsigned long high = low + OVERFLOW_STACK_SIZE;

	return (struct stack_info) {
		.low = low,
		.high = high,
	};
}

static struct stack_info stackinfo_get_hyp(void)
{
	struct kvm_nvhe_stacktrace_info *stacktrace_info
				= this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
	unsigned long low = (unsigned long)stacktrace_info->stack_base;
	unsigned long high = low + NVHE_STACK_SIZE;

	return (struct stack_info) {
		.low = low,
		.high = high,
	};
}

static struct stack_info stackinfo_get_hyp_kern_va(void)
{
	unsigned long low = (unsigned long)*this_cpu_ptr(&kvm_arm_hyp_stack_base);
	unsigned long high = low + NVHE_STACK_SIZE;

	return (struct stack_info) {
		.low = low,
		.high = high,
	};
}

/*
 * kvm_nvhe_stack_kern_va - Convert KVM nVHE HYP stack addresses to a kernel VAs
 *
 * The nVHE hypervisor stack is mapped in the flexible 'private' VA range, to
 * allow for guard pages below the stack. Consequently, the fixed offset address
 * translation macros won't work here.
 *
 * The kernel VA is calculated as an offset from the kernel VA of the hypervisor
 * stack base.
 *
 * Returns true on success and updates @addr to its corresponding kernel VA;
 * otherwise returns false.
 */
static bool kvm_nvhe_stack_kern_va(unsigned long *addr, unsigned long size)
{
	struct stack_info stack_hyp, stack_kern;

	stack_hyp = stackinfo_get_hyp();
	stack_kern = stackinfo_get_hyp_kern_va();
	if (stackinfo_on_stack(&stack_hyp, *addr, size))
		goto found;

	stack_hyp = stackinfo_get_overflow();
	stack_kern = stackinfo_get_overflow_kern_va();
	if (stackinfo_on_stack(&stack_hyp, *addr, size))
		goto found;

	return false;

found:
	*addr = *addr - stack_hyp.low + stack_kern.low;
	return true;
}

/*
 * Convert a KVN nVHE HYP frame record address to a kernel VA
 */
static bool kvm_nvhe_stack_kern_record_va(unsigned long *addr)
{
	return kvm_nvhe_stack_kern_va(addr, 16);
}

static int unwind_next(struct unwind_state *state)
{
	/*
	 * The FP is in the hypervisor VA space. Convert it to the kernel VA
	 * space so it can be unwound by the regular unwind functions.
	 */
	if (!kvm_nvhe_stack_kern_record_va(&state->fp))
		return -EINVAL;

	return unwind_next_frame_record(state);
}

static void unwind(struct unwind_state *state,
		   stack_trace_consume_fn consume_entry, void *cookie)
{
	while (1) {
		int ret;

		if (!consume_entry(cookie, state->pc))
			break;
		ret = unwind_next(state);
		if (ret < 0)
			break;
	}
}

/*
 * kvm_nvhe_dump_backtrace_entry - Symbolize and print an nVHE backtrace entry
 *
 * @arg    : the hypervisor offset, used for address translation
 * @where  : the program counter corresponding to the stack frame
 */
static bool kvm_nvhe_dump_backtrace_entry(void *arg, unsigned long where)
{
	unsigned long va_mask = GENMASK_ULL(__hyp_va_bits - 1, 0);
	unsigned long hyp_offset = (unsigned long)arg;

	/* Mask tags and convert to kern addr */
	where = (where & va_mask) + hyp_offset;
	kvm_err(" [<%016lx>] %pB\n", where, (void *)(where + kaslr_offset()));

	return true;
}

static void kvm_nvhe_dump_backtrace_start(void)
{
	kvm_err("nVHE call trace:\n");
}

static void kvm_nvhe_dump_backtrace_end(void)
{
	kvm_err("---[ end nVHE call trace ]---\n");
}

/*
 * hyp_dump_backtrace - Dump the non-protected nVHE backtrace.
 *
 * @hyp_offset: hypervisor offset, used for address translation.
 *
 * The host can directly access HYP stack pages in non-protected
 * mode, so the unwinding is done directly from EL1. This removes
 * the need for shared buffers between host and hypervisor for
 * the stacktrace.
 */
static void hyp_dump_backtrace(unsigned long hyp_offset)
{
	struct kvm_nvhe_stacktrace_info *stacktrace_info;
	struct stack_info stacks[] = {
		stackinfo_get_overflow_kern_va(),
		stackinfo_get_hyp_kern_va(),
	};
	struct unwind_state state = {
		.stacks = stacks,
		.nr_stacks = ARRAY_SIZE(stacks),
	};

	stacktrace_info = this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);

	kvm_nvhe_unwind_init(&state, stacktrace_info->fp, stacktrace_info->pc);

	kvm_nvhe_dump_backtrace_start();
	unwind(&state, kvm_nvhe_dump_backtrace_entry, (void *)hyp_offset);
	kvm_nvhe_dump_backtrace_end();
}

#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)],
			 pkvm_stacktrace);

/*
 * pkvm_dump_backtrace - Dump the protected nVHE HYP backtrace.
 *
 * @hyp_offset: hypervisor offset, used for address translation.
 *
 * Dumping of the pKVM HYP backtrace is done by reading the
 * stack addresses from the shared stacktrace buffer, since the
 * host cannot directly access hypervisor memory in protected
 * mode.
 */
static void pkvm_dump_backtrace(unsigned long hyp_offset)
{
	unsigned long *stacktrace
		= (unsigned long *) this_cpu_ptr_nvhe_sym(pkvm_stacktrace);
	int i;

	kvm_nvhe_dump_backtrace_start();
	/* The saved stacktrace is terminated by a null entry */
	for (i = 0;
	     i < ARRAY_SIZE(kvm_nvhe_sym(pkvm_stacktrace)) && stacktrace[i];
	     i++)
		kvm_nvhe_dump_backtrace_entry((void *)hyp_offset, stacktrace[i]);
	kvm_nvhe_dump_backtrace_end();
}
#else	/* !CONFIG_PROTECTED_NVHE_STACKTRACE */
static void pkvm_dump_backtrace(unsigned long hyp_offset)
{
	kvm_err("Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE\n");
}
#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */

/*
 * kvm_nvhe_dump_backtrace - Dump KVM nVHE hypervisor backtrace.
 *
 * @hyp_offset: hypervisor offset, used for address translation.
 */
void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
{
	if (is_protected_kvm_enabled())
		pkvm_dump_backtrace(hyp_offset);
	else
		hyp_dump_backtrace(hyp_offset);
}