stacktrace.c

// SPDX-License-Identifier: GPL-2.0

/*
 * Stack trace utility functions etc.
 *
 * Copyright 2008 Christoph Hellwig, IBM Corp.
 * Copyright 2018 SUSE Linux GmbH
 * Copyright 2018 Nick Piggin, Michael Ellerman, IBM Corp.
 */

#include <linux/delay.h>
#include <linux/export.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/nmi.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <linux/ftrace.h>
#include <asm/kprobes.h>

#include <asm/paca.h>

void __no_sanitize_address arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
					   struct task_struct *task, struct pt_regs *regs)
{
	unsigned long sp;

	if (regs && !consume_entry(cookie, regs->nip))
		return;

	if (regs)
		sp = regs->gpr[1];
	else if (task == current)
		sp = current_stack_frame();
	else
		sp = task->thread.ksp;

	for (;;) {
		unsigned long *stack = (unsigned long *) sp;
		unsigned long newsp, ip;

		if (!validate_sp(sp, task, STACK_FRAME_OVERHEAD))
			return;

		newsp = stack[0];
		ip = stack[STACK_FRAME_LR_SAVE];

		if (!consume_entry(cookie, ip))
			return;

		sp = newsp;
	}
}

/*
 * This function returns an error if it detects any unreliable features of the
 * stack.  Otherwise it guarantees that the stack trace is reliable.
 *
 * If the task is not 'current', the caller *must* ensure the task is inactive.
 */
int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
						   void *cookie, struct task_struct *task)
{
	unsigned long sp;
	unsigned long newsp;
	unsigned long stack_page = (unsigned long)task_stack_page(task);
	unsigned long stack_end;
	int graph_idx = 0;
	bool firstframe;

	stack_end = stack_page + THREAD_SIZE;
	if (!is_idle_task(task)) {
		/*
		 * For user tasks, this is the SP value loaded on
		 * kernel entry, see "PACAKSAVE(r13)" in _switch() and
		 * system_call_common()/EXCEPTION_PROLOG_COMMON().
		 *
		 * Likewise for non-swapper kernel threads,
		 * this also happens to be the top of the stack
		 * as setup by copy_thread().
		 *
		 * Note that stack backlinks are not properly setup by
		 * copy_thread() and thus, a forked task() will have
		 * an unreliable stack trace until it's been
		 * _switch()'ed to for the first time.
		 */
		stack_end -= STACK_FRAME_OVERHEAD + sizeof(struct pt_regs);
	} else {
		/*
		 * idle tasks have a custom stack layout,
		 * c.f. cpu_idle_thread_init().
		 */
		stack_end -= STACK_FRAME_OVERHEAD;
	}

	if (task == current)
		sp = current_stack_frame();
	else
		sp = task->thread.ksp;

	if (sp < stack_page + sizeof(struct thread_struct) ||
	    sp > stack_end - STACK_FRAME_MIN_SIZE) {
		return -EINVAL;
	}

	for (firstframe = true; sp != stack_end;
	     firstframe = false, sp = newsp) {
		unsigned long *stack = (unsigned long *) sp;
		unsigned long ip;

		/* sanity check: ABI requires SP to be aligned 16 bytes. */
		if (sp & 0xF)
			return -EINVAL;

		newsp = stack[0];
		/* Stack grows downwards; unwinder may only go up. */
		if (newsp <= sp)
			return -EINVAL;

		if (newsp != stack_end &&
		    newsp > stack_end - STACK_FRAME_MIN_SIZE) {
			return -EINVAL; /* invalid backlink, too far up. */
		}

		/*
		 * We can only trust the bottom frame's backlink, the
		 * rest of the frame may be uninitialized, continue to
		 * the next.
		 */
		if (firstframe)
			continue;

		/* Mark stacktraces with exception frames as unreliable. */
		if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
		    stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
			return -EINVAL;
		}

		/* Examine the saved LR: it must point into kernel code. */
		ip = stack[STACK_FRAME_LR_SAVE];
		if (!__kernel_text_address(ip))
			return -EINVAL;

		/*
		 * FIXME: IMHO these tests do not belong in
		 * arch-dependent code, they are generic.
		 */
		ip = ftrace_graph_ret_addr(task, &graph_idx, ip, stack);
#ifdef CONFIG_KPROBES
		/*
		 * Mark stacktraces with kretprobed functions on them
		 * as unreliable.
		 */
		if (ip == (unsigned long)kretprobe_trampoline)
			return -EINVAL;
#endif

		if (!consume_entry(cookie, ip))
			return -EINVAL;
	}
	return 0;
}

#if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)
static void handle_backtrace_ipi(struct pt_regs *regs)
{
	nmi_cpu_backtrace(regs);
}

static void raise_backtrace_ipi(cpumask_t *mask)
{
	struct paca_struct *p;
	unsigned int cpu;
	u64 delay_us;

	for_each_cpu(cpu, mask) {
		if (cpu == smp_processor_id()) {
			handle_backtrace_ipi(NULL);
			continue;
		}

		delay_us = 5 * USEC_PER_SEC;

		if (smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, delay_us)) {
			// Now wait up to 5s for the other CPU to do its backtrace
			while (cpumask_test_cpu(cpu, mask) && delay_us) {
				udelay(1);
				delay_us--;
			}

			// Other CPU cleared itself from the mask
			if (delay_us)
				continue;
		}

		p = paca_ptrs[cpu];

		cpumask_clear_cpu(cpu, mask);

		pr_warn("CPU %d didn't respond to backtrace IPI, inspecting paca.\n", cpu);
		if (!virt_addr_valid(p)) {
			pr_warn("paca pointer appears corrupt? (%px)\n", p);
			continue;
		}

		pr_warn("irq_soft_mask: 0x%02x in_mce: %d in_nmi: %d",
			p->irq_soft_mask, p->in_mce, p->in_nmi);

		if (virt_addr_valid(p->__current))
			pr_cont(" current: %d (%s)\n", p->__current->pid,
				p->__current->comm);
		else
			pr_cont(" current pointer corrupt? (%px)\n", p->__current);

		pr_warn("Back trace of paca->saved_r1 (0x%016llx) (possibly stale):\n", p->saved_r1);
		show_stack(p->__current, (unsigned long *)p->saved_r1, KERN_WARNING);
	}
}

void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
{
	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
}
#endif /* defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) */