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// SPDX-License-Identifier: GPL-2.0-only
/*
* Stack tracing support
*
* Copyright (C) 2012 ARM Ltd.
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <asm/irq.h>
#include <asm/pointer_auth.h>
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>
/*
* AArch64 PCS assigns the frame pointer to x29.
*
* A simple function prologue looks like this:
* sub sp, sp, #0x10
* stp x29, x30, [sp]
* mov x29, sp
*
* A simple function epilogue looks like this:
* mov sp, x29
* ldp x29, x30, [sp]
* add sp, sp, #0x10
*/
static notrace void start_backtrace(struct stackframe *frame, unsigned long fp,
unsigned long pc)
{
frame->fp = fp;
frame->pc = pc;
#ifdef CONFIG_KRETPROBES
frame->kr_cur = NULL;
#endif
/*
* Prime the first unwind.
*
* In unwind_frame() we'll check that the FP points to a valid stack,
* which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
* treated as a transition to whichever stack that happens to be. The
* prev_fp value won't be used, but we set it to 0 such that it is
* definitely not an accessible stack address.
*/
bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
frame->prev_fp = 0;
frame->prev_type = STACK_TYPE_UNKNOWN;
}
NOKPROBE_SYMBOL(start_backtrace);
/*
* Unwind from one frame record (A) to the next frame record (B).
*
* We terminate early if the location of B indicates a malformed chain of frame
* records (e.g. a cycle), determined based on the location and fp value of A
* and the location (but not the fp value) of B.
*/
static int notrace unwind_frame(struct task_struct *tsk,
struct stackframe *frame)
{
unsigned long fp = frame->fp;
struct stack_info info;
if (!tsk)
tsk = current;
/* Final frame; nothing to unwind */
if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
return -ENOENT;
if (fp & 0x7)
return -EINVAL;
if (!on_accessible_stack(tsk, fp, 16, &info))
return -EINVAL;
if (test_bit(info.type, frame->stacks_done))
return -EINVAL;
/*
* As stacks grow downward, any valid record on the same stack must be
* at a strictly higher address than the prior record.
*
* Stacks can nest in several valid orders, e.g.
*
* TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
* TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
*
* ... but the nesting itself is strict. Once we transition from one
* stack to another, it's never valid to unwind back to that first
* stack.
*/
if (info.type == frame->prev_type) {
if (fp <= frame->prev_fp)
return -EINVAL;
} else {
set_bit(frame->prev_type, frame->stacks_done);
}
/*
* Record this frame record's values and location. The prev_fp and
* prev_type are only meaningful to the next unwind_frame() invocation.
*/
frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
frame->prev_fp = fp;
frame->prev_type = info.type;
frame->pc = ptrauth_strip_insn_pac(frame->pc);
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
if (tsk->ret_stack &&
(frame->pc == (unsigned long)return_to_handler)) {
unsigned long orig_pc;
/*
* This is a case where function graph tracer has
* modified a return address (LR) in a stack frame
* to hook a function return.
* So replace it to an original value.
*/
orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc,
(void *)frame->fp);
if (WARN_ON_ONCE(frame->pc == orig_pc))
return -EINVAL;
frame->pc = orig_pc;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#ifdef CONFIG_KRETPROBES
if (is_kretprobe_trampoline(frame->pc))
frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
#endif
return 0;
}
NOKPROBE_SYMBOL(unwind_frame);
static void notrace walk_stackframe(struct task_struct *tsk,
struct stackframe *frame,
bool (*fn)(void *, unsigned long), void *data)
{
while (1) {
int ret;
if (!fn(data, frame->pc))
break;
ret = unwind_frame(tsk, frame);
if (ret < 0)
break;
}
}
NOKPROBE_SYMBOL(walk_stackframe);
static bool dump_backtrace_entry(void *arg, unsigned long where)
{
char *loglvl = arg;
printk("%s %pSb\n", loglvl, (void *)where);
return true;
}
void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
const char *loglvl)
{
pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
if (regs && user_mode(regs))
return;
if (!tsk)
tsk = current;
if (!try_get_task_stack(tsk))
return;
printk("%sCall trace:\n", loglvl);
arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs);
put_task_stack(tsk);
}
void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
{
dump_backtrace(NULL, tsk, loglvl);
barrier();
}
noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
void *cookie, struct task_struct *task,
struct pt_regs *regs)
{
struct stackframe frame;
if (regs)
start_backtrace(&frame, regs->regs[29], regs->pc);
else if (task == current)
start_backtrace(&frame,
(unsigned long)__builtin_frame_address(1),
(unsigned long)__builtin_return_address(0));
else
start_backtrace(&frame, thread_saved_fp(task),
thread_saved_pc(task));
walk_stackframe(task, &frame, consume_entry, cookie);
}
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