tile/kernel/stack.c

/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/pfn.h>
#include <linux/kallsyms.h>
#include <linux/stacktrace.h>
#include <linux/uaccess.h>
#include <linux/mmzone.h>
#include <linux/dcache.h>
#include <linux/fs.h>
#include <linux/hardirq.h>
#include <linux/string.h>
#include <asm/backtrace.h>
#include <asm/page.h>
#include <asm/ucontext.h>
#include <asm/switch_to.h>
#include <asm/sigframe.h>
#include <asm/stack.h>
#include <asm/vdso.h>
#include <arch/abi.h>
#include <arch/interrupts.h>

#define KBT_ONGOING	0  /* Backtrace still ongoing */
#define KBT_DONE	1  /* Backtrace cleanly completed */
#define KBT_RUNNING	2  /* Can't run backtrace on a running task */
#define KBT_LOOP	3  /* Backtrace entered a loop */

/* Is address on the specified kernel stack? */
static int in_kernel_stack(struct KBacktraceIterator *kbt, unsigned long sp)
{
	ulong kstack_base = (ulong) kbt->task->stack;
	if (kstack_base == 0)  /* corrupt task pointer; just follow stack... */
		return sp >= PAGE_OFFSET && sp < (unsigned long)high_memory;
	return sp >= kstack_base && sp < kstack_base + THREAD_SIZE;
}

/* Callback for backtracer; basically a glorified memcpy */
static bool read_memory_func(void *result, unsigned long address,
			     unsigned int size, void *vkbt)
{
	int retval;
	struct KBacktraceIterator *kbt = (struct KBacktraceIterator *)vkbt;

	if (address == 0)
		return 0;
	if (__kernel_text_address(address)) {
		/* OK to read kernel code. */
	} else if (address >= PAGE_OFFSET) {
		/* We only tolerate kernel-space reads of this task's stack */
		if (!in_kernel_stack(kbt, address))
			return 0;
	} else if (!kbt->is_current) {
		return 0;	/* can't read from other user address spaces */
	}
	pagefault_disable();
	retval = __copy_from_user_inatomic(result,
					   (void __user __force *)address,
					   size);
	pagefault_enable();
	return (retval == 0);
}

/* Return a pt_regs pointer for a valid fault handler frame */
static struct pt_regs *valid_fault_handler(struct KBacktraceIterator* kbt)
{
	const char *fault = NULL;  /* happy compiler */
	char fault_buf[64];
	unsigned long sp = kbt->it.sp;
	struct pt_regs *p;

	if (sp % sizeof(long) != 0)
		return NULL;
	if (!in_kernel_stack(kbt, sp))
		return NULL;
	if (!in_kernel_stack(kbt, sp + C_ABI_SAVE_AREA_SIZE + PTREGS_SIZE-1))
		return NULL;
	p = (struct pt_regs *)(sp + C_ABI_SAVE_AREA_SIZE);
	if (p->faultnum == INT_SWINT_1 || p->faultnum == INT_SWINT_1_SIGRETURN)
		fault = "syscall";
	else {
		if (kbt->verbose) {     /* else we aren't going to use it */
			snprintf(fault_buf, sizeof(fault_buf),
				 "interrupt %ld", p->faultnum);
			fault = fault_buf;
		}
	}
	if (EX1_PL(p->ex1) == KERNEL_PL &&
	    __kernel_text_address(p->pc) &&
	    in_kernel_stack(kbt, p->sp) &&
	    p->sp >= sp) {
		if (kbt->verbose)
			pr_err("  <%s while in kernel mode>\n", fault);
	} else if (user_mode(p) &&
		   p->sp < PAGE_OFFSET && p->sp != 0) {
		if (kbt->verbose)
			pr_err("  <%s while in user mode>\n", fault);
	} else {
		if (kbt->verbose && (p->pc != 0 || p->sp != 0 || p->ex1 != 0))
			pr_err("  (odd fault: pc %#lx, sp %#lx, ex1 %#lx?)\n",
			       p->pc, p->sp, p->ex1);
		return NULL;
	}
	if (kbt->profile && ((1ULL << p->faultnum) & QUEUED_INTERRUPTS) != 0)
		return NULL;
	return p;
}

/* Is the iterator pointing to a sigreturn trampoline? */
static int is_sigreturn(struct KBacktraceIterator *kbt)
{
	return kbt->task->mm &&
		(kbt->it.pc == ((ulong)kbt->task->mm->context.vdso_base +
				(ulong)&__vdso_rt_sigreturn));
}

/* Return a pt_regs pointer for a valid signal handler frame */
static struct pt_regs *valid_sigframe(struct KBacktraceIterator* kbt,
				      struct rt_sigframe* kframe)
{
	BacktraceIterator *b = &kbt->it;

	if (is_sigreturn(kbt) && b->sp < PAGE_OFFSET &&
	    b->sp % sizeof(long) == 0) {
		int retval;
		pagefault_disable();
		retval = __copy_from_user_inatomic(
			kframe, (void __user __force *)b->sp,
			sizeof(*kframe));
		pagefault_enable();
		if (retval != 0 ||
		    (unsigned int)(kframe->info.si_signo) >= _NSIG)
			return NULL;
		if (kbt->verbose) {
			pr_err("  <received signal %d>\n",
			       kframe->info.si_signo);
		}
		return (struct pt_regs *)&kframe->uc.uc_mcontext;
	}
	return NULL;
}

static int KBacktraceIterator_restart(struct KBacktraceIterator *kbt)
{
	struct pt_regs *p;
	struct rt_sigframe kframe;

	p = valid_fault_handler(kbt);
	if (p == NULL)
		p = valid_sigframe(kbt, &kframe);
	if (p == NULL)
		return 0;
	backtrace_init(&kbt->it, read_memory_func, kbt,
		       p->pc, p->lr, p->sp, p->regs[52]);
	kbt->new_context = 1;
	return 1;
}

/* Find a frame that isn't a sigreturn, if there is one. */
static int KBacktraceIterator_next_item_inclusive(
	struct KBacktraceIterator *kbt)
{
	for (;;) {
		do {
			if (!is_sigreturn(kbt))
				return KBT_ONGOING;
		} while (backtrace_next(&kbt->it));

		if (!KBacktraceIterator_restart(kbt))
			return KBT_DONE;
	}
}

/*
 * If the current sp is on a page different than what we recorded
 * as the top-of-kernel-stack last time we context switched, we have
 * probably blown the stack, and nothing is going to work out well.
 * If we can at least get out a warning, that may help the debug,
 * though we probably won't be able to backtrace into the code that
 * actually did the recursive damage.
 */
static void validate_stack(struct pt_regs *regs)
{
	int cpu = raw_smp_processor_id();
	unsigned long ksp0 = get_current_ksp0();
	unsigned long ksp0_base = ksp0 & -THREAD_SIZE;
	unsigned long sp = stack_pointer;

	if (EX1_PL(regs->ex1) == KERNEL_PL && regs->sp >= ksp0) {
		pr_err("WARNING: cpu %d: kernel stack %#lx..%#lx underrun!\n"
		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
		       cpu, ksp0_base, ksp0, sp, regs->sp, regs->pc, regs->lr);
	}

	else if (sp < ksp0_base + sizeof(struct thread_info)) {
		pr_err("WARNING: cpu %d: kernel stack %#lx..%#lx overrun!\n"
		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
		       cpu, ksp0_base, ksp0, sp, regs->sp, regs->pc, regs->lr);
	}
}

void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
			     struct task_struct *t, struct pt_regs *regs)
{
	unsigned long pc, lr, sp, r52;
	int is_current;

	/*
	 * Set up callback information.  We grab the kernel stack base
	 * so we will allow reads of that address range.
	 */
	is_current = (t == NULL || t == current);
	kbt->is_current = is_current;
	if (is_current)
		t = validate_current();
	kbt->task = t;
	kbt->verbose = 0;   /* override in caller if desired */
	kbt->profile = 0;   /* override in caller if desired */
	kbt->end = KBT_ONGOING;
	kbt->new_context = 1;
	if (is_current)
		validate_stack(regs);

	if (regs == NULL) {
		if (is_current || t->state == TASK_RUNNING) {
			/* Can't do this; we need registers */
			kbt->end = KBT_RUNNING;
			return;
		}
		pc = get_switch_to_pc();
		lr = t->thread.pc;
		sp = t->thread.ksp;
		r52 = 0;
	} else {
		pc = regs->pc;
		lr = regs->lr;
		sp = regs->sp;
		r52 = regs->regs[52];
	}

	backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
}
EXPORT_SYMBOL(KBacktraceIterator_init);

int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
{
	return kbt->end != KBT_ONGOING;
}
EXPORT_SYMBOL(KBacktraceIterator_end);

void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
{
	unsigned long old_pc = kbt->it.pc, old_sp = kbt->it.sp;
	kbt->new_context = 0;
	if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
		kbt->end = KBT_DONE;
		return;
	}
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
	if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
		/* Trapped in a loop; give up. */
		kbt->end = KBT_LOOP;
	}
}
EXPORT_SYMBOL(KBacktraceIterator_next);

static void describe_addr(struct KBacktraceIterator *kbt,
			  unsigned long address,
			  int have_mmap_sem, char *buf, size_t bufsize)
{
	struct vm_area_struct *vma;
	size_t namelen, remaining;
	unsigned long size, offset, adjust;
	char *p, *modname;
	const char *name;
	int rc;

	/*
	 * Look one byte back for every caller frame (i.e. those that
	 * aren't a new context) so we look up symbol data for the
	 * call itself, not the following instruction, which may be on
	 * a different line (or in a different function).
	 */
	adjust = !kbt->new_context;
	address -= adjust;

	if (address >= PAGE_OFFSET) {
		/* Handle kernel symbols. */
		BUG_ON(bufsize < KSYM_NAME_LEN);
		name = kallsyms_lookup(address, &size, &offset,
				       &modname, buf);
		if (name == NULL) {
			buf[0] = '\0';
			return;
		}
		namelen = strlen(buf);
		remaining = (bufsize - 1) - namelen;
		p = buf + namelen;
		rc = snprintf(p, remaining, "+%#lx/%#lx ",
			      offset + adjust, size);
		if (modname && rc < remaining)
			snprintf(p + rc, remaining - rc, "[%s] ", modname);
		buf[bufsize-1] = '\0';
		return;
	}

	/* If we don't have the mmap_sem, we can't show any more info. */
	buf[0] = '\0';
	if (!have_mmap_sem)
		return;

	/* Find vma info. */
	vma = find_vma(kbt->task->mm, address);
	if (vma == NULL || address < vma->vm_start) {
		snprintf(buf, bufsize, "[unmapped address] ");
		return;
	}

	if (vma->vm_file) {
		p = file_path(vma->vm_file, buf, bufsize);
		if (IS_ERR(p))
			p = "?";
		name = kbasename(p);
	} else {
		name = "anon";
	}

	/* Generate a string description of the vma info. */
	namelen = strlen(name);
	remaining = (bufsize - 1) - namelen;
	memmove(buf, name, namelen);
	snprintf(buf + namelen, remaining, "[%lx+%lx] ",
		 vma->vm_start, vma->vm_end - vma->vm_start);
}

/*
 * Avoid possible crash recursion during backtrace.  If it happens, it
 * makes it easy to lose the actual root cause of the failure, so we
 * put a simple guard on all the backtrace loops.
 */
static bool start_backtrace(void)
{
	if (current_thread_info()->in_backtrace) {
		pr_err("Backtrace requested while in backtrace!\n");
		return false;
	}
	current_thread_info()->in_backtrace = true;
	return true;
}

static void end_backtrace(void)
{
	current_thread_info()->in_backtrace = false;
}

/*
 * This method wraps the backtracer's more generic support.
 * It is only invoked from the architecture-specific code; show_stack()
 * and dump_stack() are architecture-independent entry points.
 */
void tile_show_stack(struct KBacktraceIterator *kbt)
{
	int i;
	int have_mmap_sem = 0;

	if (!start_backtrace())
		return;
	kbt->verbose = 1;
	i = 0;
	for (; !KBacktraceIterator_end(kbt); KBacktraceIterator_next(kbt)) {
		char namebuf[KSYM_NAME_LEN+100];
		unsigned long address = kbt->it.pc;

		/*
		 * Try to acquire the mmap_sem as we pass into userspace.
		 * If we're in an interrupt context, don't even try, since
		 * it's not safe to call e.g. d_path() from an interrupt,
		 * since it uses spin locks without disabling interrupts.
		 * Note we test "kbt->task == current", not "kbt->is_current",
		 * since we're checking that "current" will work in d_path().
		 */
		if (kbt->task == current && address < PAGE_OFFSET &&
		    !have_mmap_sem && kbt->task->mm && !in_interrupt()) {
			have_mmap_sem =
				down_read_trylock(&kbt->task->mm->mmap_sem);
		}

		describe_addr(kbt, address, have_mmap_sem,
			      namebuf, sizeof(namebuf));

		pr_err("  frame %d: 0x%lx %s(sp 0x%lx)\n",
		       i++, address, namebuf, (unsigned long)(kbt->it.sp));

		if (i >= 100) {
			pr_err("Stack dump truncated (%d frames)\n", i);
			break;
		}
	}
	if (kbt->end == KBT_LOOP)
		pr_err("Stack dump stopped; next frame identical to this one\n");
	if (have_mmap_sem)
		up_read(&kbt->task->mm->mmap_sem);
	end_backtrace();
}
EXPORT_SYMBOL(tile_show_stack);

static struct pt_regs *regs_to_pt_regs(struct pt_regs *regs,
				       ulong pc, ulong lr, ulong sp, ulong r52)
{
	memset(regs, 0, sizeof(struct pt_regs));
	regs->pc = pc;
	regs->lr = lr;
	regs->sp = sp;
	regs->regs[52] = r52;
	return regs;
}

/* Deprecated function currently only used by kernel_double_fault(). */
void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
{
	struct KBacktraceIterator kbt;
	struct pt_regs regs;

	regs_to_pt_regs(&regs, pc, lr, sp, r52);
	KBacktraceIterator_init(&kbt, NULL, &regs);
	tile_show_stack(&kbt);
}

/* This is called from KBacktraceIterator_init_current() */
void _KBacktraceIterator_init_current(struct KBacktraceIterator *kbt, ulong pc,
				      ulong lr, ulong sp, ulong r52)
{
	struct pt_regs regs;
	KBacktraceIterator_init(kbt, NULL,
				regs_to_pt_regs(&regs, pc, lr, sp, r52));
}

/*
 * Called from sched_show_task() with task != NULL, or dump_stack()
 * with task == NULL.  The esp argument is always NULL.
 */
void show_stack(struct task_struct *task, unsigned long *esp)
{
	struct KBacktraceIterator kbt;
	if (task == NULL || task == current) {
		KBacktraceIterator_init_current(&kbt);
		KBacktraceIterator_next(&kbt);  /* don't show first frame */
	} else {
		KBacktraceIterator_init(&kbt, task, NULL);
	}
	tile_show_stack(&kbt);
}

#ifdef CONFIG_STACKTRACE

/* Support generic Linux stack API too */

static void save_stack_trace_common(struct task_struct *task,
				    struct pt_regs *regs,
				    bool user,
				    struct stack_trace *trace)
{
	struct KBacktraceIterator kbt;
	int skip = trace->skip;
	int i = 0;

	if (!start_backtrace())
		goto done;
	if (regs != NULL) {
		KBacktraceIterator_init(&kbt, NULL, regs);
	} else if (task == NULL || task == current) {
		KBacktraceIterator_init_current(&kbt);
		skip++;  /* don't show KBacktraceIterator_init_current */
	} else {
		KBacktraceIterator_init(&kbt, task, NULL);
	}
	for (; !KBacktraceIterator_end(&kbt); KBacktraceIterator_next(&kbt)) {
		if (skip) {
			--skip;
			continue;
		}
		if (i >= trace->max_entries ||
		    (!user && kbt.it.pc < PAGE_OFFSET))
			break;
		trace->entries[i++] = kbt.it.pc;
	}
	end_backtrace();
done:
	if (i < trace->max_entries)
		trace->entries[i++] = ULONG_MAX;
	trace->nr_entries = i;
}

void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
{
	save_stack_trace_common(task, NULL, false, trace);
}
EXPORT_SYMBOL(save_stack_trace_tsk);

void save_stack_trace(struct stack_trace *trace)
{
	save_stack_trace_common(NULL, NULL, false, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace);

void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
{
	save_stack_trace_common(NULL, regs, false, trace);
}

void save_stack_trace_user(struct stack_trace *trace)
{
	/* Trace user stack if we are not a kernel thread. */
	if (current->mm)
		save_stack_trace_common(NULL, task_pt_regs(current),
					true, trace);
	else if (trace->nr_entries < trace->max_entries)
		trace->entries[trace->nr_entries++] = ULONG_MAX;
}
#endif

/* In entry.S */
EXPORT_SYMBOL(KBacktraceIterator_init_current);