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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>
/*
* A snapshot of a frame record or fp/lr register values, along with some
* accounting information necessary for robust unwinding.
*
* @fp: The fp value in the frame record (or the real fp)
* @pc: The lr value in the frame record (or the real lr)
*
* @stacks_done: Stacks which have been entirely unwound, for which it is no
* longer valid to unwind to.
*
* @prev_fp: The fp that pointed to this frame record, or a synthetic value
* of 0. This is used to ensure that within a stack, each
* subsequent frame record is at an increasing address.
* @prev_type: The type of stack this frame record was on, or a synthetic
* value of STACK_TYPE_UNKNOWN. This is used to detect a
* transition from one stack to another.
*
* @kr_cur: When KRETPROBES is selected, holds the kretprobe instance
* associated with the most recently encountered replacement lr
* value.
*/
struct unwind_state {
unsigned long fp;
unsigned long pc;
DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
unsigned long prev_fp;
enum stack_type prev_type;
#ifdef CONFIG_KRETPROBES
struct llist_node *kr_cur;
#endif
};
static notrace void unwind_init(struct unwind_state *state, unsigned long fp,
unsigned long pc)
{
state->fp = fp;
state->pc = pc;
#ifdef CONFIG_KRETPROBES
state->kr_cur = NULL;
#endif
/*
* Prime the first unwind.
*
* In unwind_next() 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(state->stacks_done, __NR_STACK_TYPES);
state->prev_fp = 0;
state->prev_type = STACK_TYPE_UNKNOWN;
}
NOKPROBE_SYMBOL(unwind_init);
/*
* 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_next(struct task_struct *tsk,
struct unwind_state *state)
{
unsigned long fp = state->fp;
struct stack_info info;
/* 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, state->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 == state->prev_type) {
if (fp <= state->prev_fp)
return -EINVAL;
} else {
set_bit(state->prev_type, state->stacks_done);
}
/*
* Record this frame record's values and location. The prev_fp and
* prev_type are only meaningful to the next unwind_next() invocation.
*/
state->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
state->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
state->prev_fp = fp;
state->prev_type = info.type;
state->pc = ptrauth_strip_insn_pac(state->pc);
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
if (tsk->ret_stack &&
(state->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, state->pc,
(void *)state->fp);
if (WARN_ON_ONCE(state->pc == orig_pc))
return -EINVAL;
state->pc = orig_pc;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#ifdef CONFIG_KRETPROBES
if (is_kretprobe_trampoline(state->pc))
state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur);
#endif
return 0;
}
NOKPROBE_SYMBOL(unwind_next);
static void notrace unwind(struct task_struct *tsk,
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(tsk, state);
if (ret < 0)
break;
}
}
NOKPROBE_SYMBOL(unwind);
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 unwind_state state;
if (regs)
unwind_init(&state, regs->regs[29], regs->pc);
else if (task == current)
unwind_init(&state,
(unsigned long)__builtin_frame_address(1),
(unsigned long)__builtin_return_address(0));
else
unwind_init(&state, thread_saved_fp(task),
thread_saved_pc(task));
unwind(task, &state, consume_entry, cookie);
}
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