// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
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*
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*/
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#include <linux/sched/task_stack.h>
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#include <linux/stacktrace.h>
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#include <linux/security.h>
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#include <linux/kallsyms.h>
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#include <linux/seq_file.h>
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#include <linux/spinlock.h>
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#include <linux/uaccess.h>
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#include <linux/ftrace.h>
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#include <linux/module.h>
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#include <linux/sysctl.h>
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#include <linux/init.h>
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#include <asm/setup.h>
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#include "trace.h"
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#define STACK_TRACE_ENTRIES 500
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static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES];
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static unsigned stack_trace_index[STACK_TRACE_ENTRIES];
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static unsigned int stack_trace_nr_entries;
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static unsigned long stack_trace_max_size;
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static arch_spinlock_t stack_trace_max_lock =
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(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
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DEFINE_PER_CPU(int, disable_stack_tracer);
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static DEFINE_MUTEX(stack_sysctl_mutex);
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int stack_tracer_enabled;
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static void print_max_stack(void)
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{
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long i;
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int size;
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pr_emerg(" Depth Size Location (%d entries)\n"
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" ----- ---- --------\n",
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stack_trace_nr_entries);
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for (i = 0; i < stack_trace_nr_entries; i++) {
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if (i + 1 == stack_trace_nr_entries)
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size = stack_trace_index[i];
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else
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size = stack_trace_index[i] - stack_trace_index[i+1];
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pr_emerg("%3ld) %8d %5d %pS\n", i, stack_trace_index[i],
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size, (void *)stack_dump_trace[i]);
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}
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}
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/*
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* The stack tracer looks for a maximum stack at each call from a function. It
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* registers a callback from ftrace, and in that callback it examines the stack
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* size. It determines the stack size from the variable passed in, which is the
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* address of a local variable in the stack_trace_call() callback function.
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* The stack size is calculated by the address of the local variable to the top
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* of the current stack. If that size is smaller than the currently saved max
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* stack size, nothing more is done.
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*
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* If the size of the stack is greater than the maximum recorded size, then the
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* following algorithm takes place.
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*
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* For architectures (like x86) that store the function's return address before
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* saving the function's local variables, the stack will look something like
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* this:
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*
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* [ top of stack ]
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* 0: sys call entry frame
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* 10: return addr to entry code
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* 11: start of sys_foo frame
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* 20: return addr to sys_foo
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* 21: start of kernel_func_bar frame
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* 30: return addr to kernel_func_bar
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* 31: [ do trace stack here ]
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*
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* The save_stack_trace() is called returning all the functions it finds in the
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* current stack. Which would be (from the bottom of the stack to the top):
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*
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* return addr to kernel_func_bar
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* return addr to sys_foo
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* return addr to entry code
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*
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* Now to figure out how much each of these functions' local variable size is,
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* a search of the stack is made to find these values. When a match is made, it
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* is added to the stack_dump_trace[] array. The offset into the stack is saved
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* in the stack_trace_index[] array. The above example would show:
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*
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* stack_dump_trace[] | stack_trace_index[]
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* ------------------ + -------------------
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* return addr to kernel_func_bar | 30
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* return addr to sys_foo | 20
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* return addr to entry | 10
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*
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* The print_max_stack() function above, uses these values to print the size of
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* each function's portion of the stack.
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*
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* for (i = 0; i < nr_entries; i++) {
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* size = i == nr_entries - 1 ? stack_trace_index[i] :
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* stack_trace_index[i] - stack_trace_index[i+1]
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* print "%d %d %d %s\n", i, stack_trace_index[i], size, stack_dump_trace[i]);
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* }
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*
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* The above shows
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*
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* depth size location
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* ----- ---- --------
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* 0 30 10 kernel_func_bar
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* 1 20 10 sys_foo
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* 2 10 10 entry code
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*
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* Now for architectures that might save the return address after the functions
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* local variables (saving the link register before calling nested functions),
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* this will cause the stack to look a little different:
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*
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* [ top of stack ]
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* 0: sys call entry frame
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* 10: start of sys_foo_frame
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* 19: return addr to entry code << lr saved before calling kernel_func_bar
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* 20: start of kernel_func_bar frame
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* 29: return addr to sys_foo_frame << lr saved before calling next function
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* 30: [ do trace stack here ]
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*
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* Although the functions returned by save_stack_trace() may be the same, the
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* placement in the stack will be different. Using the same algorithm as above
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* would yield:
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*
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* stack_dump_trace[] | stack_trace_index[]
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* ------------------ + -------------------
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* return addr to kernel_func_bar | 30
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* return addr to sys_foo | 29
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* return addr to entry | 19
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*
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* Where the mapping is off by one:
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*
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* kernel_func_bar stack frame size is 29 - 19 not 30 - 29!
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*
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* To fix this, if the architecture sets ARCH_RET_ADDR_AFTER_LOCAL_VARS the
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* values in stack_trace_index[] are shifted by one to and the number of
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* stack trace entries is decremented by one.
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*
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* stack_dump_trace[] | stack_trace_index[]
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* ------------------ + -------------------
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* return addr to kernel_func_bar | 29
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* return addr to sys_foo | 19
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*
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* Although the entry function is not displayed, the first function (sys_foo)
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* will still include the stack size of it.
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*/
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static void check_stack(unsigned long ip, unsigned long *stack)
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{
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unsigned long this_size, flags; unsigned long *p, *top, *start;
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static int tracer_frame;
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int frame_size = READ_ONCE(tracer_frame);
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int i, x;
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this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
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this_size = THREAD_SIZE - this_size;
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/* Remove the frame of the tracer */
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this_size -= frame_size;
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if (this_size <= stack_trace_max_size)
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return;
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/* we do not handle interrupt stacks yet */
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if (!object_is_on_stack(stack))
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return;
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/* Can't do this from NMI context (can cause deadlocks) */
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if (in_nmi())
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return;
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local_irq_save(flags);
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arch_spin_lock(&stack_trace_max_lock);
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/* In case another CPU set the tracer_frame on us */
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if (unlikely(!frame_size))
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this_size -= tracer_frame;
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/* a race could have already updated it */
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if (this_size <= stack_trace_max_size)
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goto out;
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stack_trace_max_size = this_size;
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stack_trace_nr_entries = stack_trace_save(stack_dump_trace,
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ARRAY_SIZE(stack_dump_trace) - 1,
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0);
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/* Skip over the overhead of the stack tracer itself */
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for (i = 0; i < stack_trace_nr_entries; i++) {
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if (stack_dump_trace[i] == ip)
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break;
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}
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/*
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* Some archs may not have the passed in ip in the dump.
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* If that happens, we need to show everything.
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*/
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if (i == stack_trace_nr_entries)
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i = 0;
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/*
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* Now find where in the stack these are.
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*/
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x = 0;
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start = stack;
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top = (unsigned long *)
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(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
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/*
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* Loop through all the entries. One of the entries may
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* for some reason be missed on the stack, so we may
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* have to account for them. If they are all there, this
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* loop will only happen once. This code only takes place
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* on a new max, so it is far from a fast path.
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*/
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while (i < stack_trace_nr_entries) {
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int found = 0;
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stack_trace_index[x] = this_size;
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p = start;
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for (; p < top && i < stack_trace_nr_entries; p++) {
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/*
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* The READ_ONCE_NOCHECK is used to let KASAN know that
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* this is not a stack-out-of-bounds error.
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*/
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if ((READ_ONCE_NOCHECK(*p)) == stack_dump_trace[i]) {
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stack_dump_trace[x] = stack_dump_trace[i++];
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this_size = stack_trace_index[x++] =
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(top - p) * sizeof(unsigned long);
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found = 1;
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/* Start the search from here */
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start = p + 1;
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/*
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* We do not want to show the overhead
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* of the stack tracer stack in the
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* max stack. If we haven't figured
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* out what that is, then figure it out
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* now.
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*/
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if (unlikely(!tracer_frame)) {
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tracer_frame = (p - stack) *
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sizeof(unsigned long);
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stack_trace_max_size -= tracer_frame;
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}
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}
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}
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if (!found)
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i++;
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}
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#ifdef ARCH_FTRACE_SHIFT_STACK_TRACER
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/*
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* Some archs will store the link register before calling
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* nested functions. This means the saved return address
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* comes after the local storage, and we need to shift
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* for that.
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*/
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if (x > 1) {
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memmove(&stack_trace_index[0], &stack_trace_index[1],
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sizeof(stack_trace_index[0]) * (x - 1));
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x--;
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}
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#endif
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stack_trace_nr_entries = x;
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if (task_stack_end_corrupted(current)) {
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print_max_stack();
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BUG();
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}
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out:
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arch_spin_unlock(&stack_trace_max_lock);
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local_irq_restore(flags);
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}
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/* Some archs may not define MCOUNT_INSN_SIZE */
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#ifndef MCOUNT_INSN_SIZE
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# define MCOUNT_INSN_SIZE 0
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#endif
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static void
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stack_trace_call(unsigned long ip, unsigned long parent_ip,
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struct ftrace_ops *op, struct pt_regs *pt_regs)
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{
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unsigned long stack;
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preempt_disable_notrace();
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/* no atomic needed, we only modify this variable by this cpu */
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__this_cpu_inc(disable_stack_tracer);
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if (__this_cpu_read(disable_stack_tracer) != 1)
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goto out;
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/* If rcu is not watching, then save stack trace can fail */
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if (!rcu_is_watching())
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goto out;
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ip += MCOUNT_INSN_SIZE;
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check_stack(ip, &stack);
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out:
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__this_cpu_dec(disable_stack_tracer);
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/* prevent recursion in schedule */
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preempt_enable_notrace();
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}
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static struct ftrace_ops trace_ops __read_mostly =
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{
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.func = stack_trace_call,
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.flags = FTRACE_OPS_FL_RECURSION_SAFE,
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};
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static ssize_t
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stack_max_size_read(struct file *filp, char __user *ubuf,
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size_t count, loff_t *ppos)
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{
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unsigned long *ptr = filp->private_data;
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char buf[64];
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int r;
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r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
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if (r > sizeof(buf))
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r = sizeof(buf);
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return simple_read_from_buffer(ubuf, count, ppos, buf, r);
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}
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static ssize_t
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stack_max_size_write(struct file *filp, const char __user *ubuf,
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size_t count, loff_t *ppos)
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{
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long *ptr = filp->private_data;
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unsigned long val, flags;
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int ret;
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ret = kstrtoul_from_user(ubuf, count, 10, &val);
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if (ret)
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return ret;
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local_irq_save(flags);
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/*
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* In case we trace inside arch_spin_lock() or after (NMI),
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* we will cause circular lock, so we also need to increase
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* the percpu disable_stack_tracer here.
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*/
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__this_cpu_inc(disable_stack_tracer);
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arch_spin_lock(&stack_trace_max_lock);
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*ptr = val;
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arch_spin_unlock(&stack_trace_max_lock);
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__this_cpu_dec(disable_stack_tracer);
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local_irq_restore(flags);
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return count;
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}
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static const struct file_operations stack_max_size_fops = {
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.open = tracing_open_generic,
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.read = stack_max_size_read,
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.write = stack_max_size_write,
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.llseek = default_llseek,
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};
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static void *
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__next(struct seq_file *m, loff_t *pos)
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{
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long n = *pos - 1;
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if (n >= stack_trace_nr_entries)
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return NULL;
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m->private = (void *)n;
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return &m->private;
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}
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static void *
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t_next(struct seq_file *m, void *v, loff_t *pos)
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{
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(*pos)++;
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return __next(m, pos);
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}
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static void *t_start(struct seq_file *m, loff_t *pos)
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{
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local_irq_disable();
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__this_cpu_inc(disable_stack_tracer);
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arch_spin_lock(&stack_trace_max_lock);
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if (*pos == 0)
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return SEQ_START_TOKEN;
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return __next(m, pos);
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}
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static void t_stop(struct seq_file *m, void *p)
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{
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arch_spin_unlock(&stack_trace_max_lock);
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__this_cpu_dec(disable_stack_tracer);
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local_irq_enable();
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}
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static void trace_lookup_stack(struct seq_file *m, long i)
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{
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unsigned long addr = stack_dump_trace[i];
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seq_printf(m, "%pS\n", (void *)addr);
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}
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static void print_disabled(struct seq_file *m)
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{
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seq_puts(m, "#\n"
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"# Stack tracer disabled\n"
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"#\n"
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"# To enable the stack tracer, either add 'stacktrace' to the\n"
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"# kernel command line\n"
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"# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
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"#\n");
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}
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static int t_show(struct seq_file *m, void *v)
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{
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long i;
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int size;
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if (v == SEQ_START_TOKEN) {
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seq_printf(m, " Depth Size Location"
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" (%d entries)\n"
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" ----- ---- --------\n",
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stack_trace_nr_entries);
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if (!stack_tracer_enabled && !stack_trace_max_size)
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print_disabled(m);
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return 0;
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}
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i = *(long *)v;
|
|
if (i >= stack_trace_nr_entries)
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return 0;
|
|
if (i + 1 == stack_trace_nr_entries)
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size = stack_trace_index[i];
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else
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size = stack_trace_index[i] - stack_trace_index[i+1];
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seq_printf(m, "%3ld) %8d %5d ", i, stack_trace_index[i], size);
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trace_lookup_stack(m, i);
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|
return 0;
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}
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static const struct seq_operations stack_trace_seq_ops = {
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.start = t_start,
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.next = t_next,
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.stop = t_stop,
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.show = t_show,
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};
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static int stack_trace_open(struct inode *inode, struct file *file)
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{
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int ret;
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|
ret = security_locked_down(LOCKDOWN_TRACEFS);
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if (ret)
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return ret;
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|
return seq_open(file, &stack_trace_seq_ops);
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}
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static const struct file_operations stack_trace_fops = {
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.open = stack_trace_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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#ifdef CONFIG_DYNAMIC_FTRACE
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static int
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stack_trace_filter_open(struct inode *inode, struct file *file)
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{
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struct ftrace_ops *ops = inode->i_private;
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/* Checks for tracefs lockdown */
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return ftrace_regex_open(ops, FTRACE_ITER_FILTER,
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inode, file);
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}
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|
static const struct file_operations stack_trace_filter_fops = {
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.open = stack_trace_filter_open,
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.read = seq_read,
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.write = ftrace_filter_write,
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.llseek = tracing_lseek,
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.release = ftrace_regex_release,
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};
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#endif /* CONFIG_DYNAMIC_FTRACE */
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int
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stack_trace_sysctl(struct ctl_table *table, int write, void *buffer,
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size_t *lenp, loff_t *ppos)
|
{
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int was_enabled;
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int ret;
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|
mutex_lock(&stack_sysctl_mutex);
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was_enabled = !!stack_tracer_enabled;
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|
ret = proc_dointvec(table, write, buffer, lenp, ppos);
|
|
if (ret || !write || (was_enabled == !!stack_tracer_enabled))
|
goto out;
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|
if (stack_tracer_enabled)
|
register_ftrace_function(&trace_ops);
|
else
|
unregister_ftrace_function(&trace_ops);
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out:
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mutex_unlock(&stack_sysctl_mutex);
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return ret;
|
}
|
|
static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
|
|
static __init int enable_stacktrace(char *str)
|
{
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int len;
|
|
if ((len = str_has_prefix(str, "_filter=")))
|
strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
|
|
stack_tracer_enabled = 1;
|
return 1;
|
}
|
__setup("stacktrace", enable_stacktrace);
|
|
static __init int stack_trace_init(void)
|
{
|
int ret;
|
|
ret = tracing_init_dentry();
|
if (ret)
|
return 0;
|
|
trace_create_file("stack_max_size", 0644, NULL,
|
&stack_trace_max_size, &stack_max_size_fops);
|
|
trace_create_file("stack_trace", 0444, NULL,
|
NULL, &stack_trace_fops);
|
|
#ifdef CONFIG_DYNAMIC_FTRACE
|
trace_create_file("stack_trace_filter", 0644, NULL,
|
&trace_ops, &stack_trace_filter_fops);
|
#endif
|
|
if (stack_trace_filter_buf[0])
|
ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);
|
|
if (stack_tracer_enabled)
|
register_ftrace_function(&trace_ops);
|
|
return 0;
|
}
|
|
device_initcall(stack_trace_init);
|
