// SPDX-License-Identifier: GPL-2.0-only
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/interrupt.h>
#include <asm/sections.h>
#include <asm/ptrace.h>
#include <asm/bitops.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>
#define FRAME_HEADER_SIZE (sizeof(long) * 2)
unsigned long unwind_get_return_address(struct unwind_state *state)
{
if (unwind_done(state))
return 0;
return __kernel_text_address(state->ip) ? state->ip : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
{
if (unwind_done(state))
return NULL;
return state->regs ? &state->regs->ip : state->bp + 1;
}
static void unwind_dump(struct unwind_state *state)
{
static bool dumped_before = false;
bool prev_zero, zero = false;
unsigned long word, *sp;
struct stack_info stack_info = {0};
unsigned long visit_mask = 0;
if (dumped_before)
return;
dumped_before = true;
printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
state->stack_info.type, state->stack_info.next_sp,
state->stack_mask, state->graph_idx);
for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp;
sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
break;
for (; sp < stack_info.end; sp++) {
word = READ_ONCE_NOCHECK(*sp);
prev_zero = zero;
zero = word == 0;
if (zero) {
if (!prev_zero)
printk_deferred("%p: %0*x ...\n",
sp, BITS_PER_LONG/4, 0);
continue;
}
printk_deferred("%p: %0*lx (%pB)\n",
sp, BITS_PER_LONG/4, word, (void *)word);
}
}
}
static bool in_entry_code(unsigned long ip)
{
char *addr = (char *)ip;
return addr >= __entry_text_start && addr < __entry_text_end;
}
static inline unsigned long *last_frame(struct unwind_state *state)
{
return (unsigned long *)task_pt_regs(state->task) - 2;
}
static bool is_last_frame(struct unwind_state *state)
{
return state->bp == last_frame(state);
}
#ifdef CONFIG_X86_32
#define GCC_REALIGN_WORDS 3
#else
#define GCC_REALIGN_WORDS 1
#endif
static inline unsigned long *last_aligned_frame(struct unwind_state *state)
{
return last_frame(state) - GCC_REALIGN_WORDS;
}
static bool is_last_aligned_frame(struct unwind_state *state)
{
unsigned long *last_bp = last_frame(state);
unsigned long *aligned_bp = last_aligned_frame(state);
/*
* GCC can occasionally decide to realign the stack pointer and change
* the offset of the stack frame in the prologue of a function called
* by head/entry code. Examples:
*
* <start_secondary>:
* push %edi
* lea 0x8(%esp),%edi
* and $0xfffffff8,%esp
* pushl -0x4(%edi)
* push %ebp
* mov %esp,%ebp
*
* <x86_64_start_kernel>:
* lea 0x8(%rsp),%r10
* and $0xfffffffffffffff0,%rsp
* pushq -0x8(%r10)
* push %rbp
* mov %rsp,%rbp
*
* After aligning the stack, it pushes a duplicate copy of the return
* address before pushing the frame pointer.
*/
return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
}
static bool is_last_ftrace_frame(struct unwind_state *state)
{
unsigned long *last_bp = last_frame(state);
unsigned long *last_ftrace_bp = last_bp - 3;
/*
* When unwinding from an ftrace handler of a function called by entry
* code, the stack layout of the last frame is:
*
* bp
* parent ret addr
* bp
* function ret addr
* parent ret addr
* pt_regs
* -----------------
*/
return (state->bp == last_ftrace_bp &&
*state->bp == *(state->bp + 2) &&
*(state->bp + 1) == *(state->bp + 4));
}
static bool is_last_task_frame(struct unwind_state *state)
{
return is_last_frame(state) || is_last_aligned_frame(state) ||
is_last_ftrace_frame(state);
}
/*
* This determines if the frame pointer actually contains an encoded pointer to
* pt_regs on the stack. See ENCODE_FRAME_POINTER.
*/
#ifdef CONFIG_X86_64
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
unsigned long regs = (unsigned long)bp;
if (!(regs & 0x1))
return NULL;
return (struct pt_regs *)(regs & ~0x1);
}
#else
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
unsigned long regs = (unsigned long)bp;
if (regs & 0x80000000)
return NULL;
return (struct pt_regs *)(regs | 0x80000000);
}
#endif
/*
* While walking the stack, KMSAN may stomp on stale locals from other
* functions that were marked as uninitialized upon function exit, and
* now hold the call frame information for the current function (e.g. the frame
* pointer). Because KMSAN does not specifically mark call frames as
* initialized, false positive reports are possible. To prevent such reports,
* we mark the functions scanning the stack (here and below) with
* __no_kmsan_checks.
*/
__no_kmsan_checks
static bool update_stack_state(struct unwind_state *state,
unsigned long *next_bp)
{
struct stack_info *info = &state->stack_info;
enum stack_type prev_type = info->type;
struct pt_regs *regs;
unsigned long *frame, *prev_frame_end, *addr_p, addr;
size_t len;
if (state->regs)
prev_frame_end = (void *)state->regs + sizeof(*state->regs);
else
prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;
/* Is the next frame pointer an encoded pointer to pt_regs? */
regs = decode_frame_pointer(next_bp);
if (regs) {
frame = (unsigned long *)regs;
len = sizeof(*regs);
state->got_irq = true;
} else {
frame = next_bp;
len = FRAME_HEADER_SIZE;
}
/*
* If the next bp isn't on the current stack, switch to the next one.
*
* We may have to traverse multiple stacks to deal with the possibility
* that info->next_sp could point to an empty stack and the next bp
* could be on a subsequent stack.
*/
while (!on_stack(info, frame, len))
if (get_stack_info(info->next_sp, state->task, info,
&state->stack_mask))
return false;
/* Make sure it only unwinds up and doesn't overlap the prev frame: */
if (state->orig_sp && state->stack_info.type == prev_type &&
frame < prev_frame_end)
return false;
/* Move state to the next frame: */
if (regs) {
state->regs = regs;
state->bp = NULL;
} else {
state->bp = next_bp;
state->regs = NULL;
}
/* Save the return address: */
if (state->regs && user_mode(state->regs))
state->ip = 0;
else {
addr_p = unwind_get_return_address_ptr(state);
addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
state->ip = unwind_recover_ret_addr(state, addr, addr_p);
}
/* Save the original stack pointer for unwind_dump(): */
if (!state->orig_sp)
state->orig_sp = frame;
return true;
}
__no_kmsan_checks
bool unwind_next_frame(struct unwind_state *state)
{
struct pt_regs *regs;
unsigned long *next_bp;
if (unwind_done(state))
return false;
/* Have we reached the end? */
if (state->regs && user_mode(state->regs))
goto the_end;
if (is_last_task_frame(state)) {
regs = task_pt_regs(state->task);
/*
* kthreads (other than the boot CPU's idle thread) have some
* partial regs at the end of their stack which were placed
* there by copy_thread(). But the regs don't have any
* useful information, so we can skip them.
*
* This user_mode() check is slightly broader than a PF_KTHREAD
* check because it also catches the awkward situation where a
* newly forked kthread transitions into a user task by calling
* kernel_execve(), which eventually clears PF_KTHREAD.
*/
if (!user_mode(regs))
goto the_end;
/*
* We're almost at the end, but not quite: there's still the
* syscall regs frame. Entry code doesn't encode the regs
* pointer for syscalls, so we have to set it manually.
*/
state->regs = regs;
state->bp = NULL;
state->ip = 0;
return true;
}
/* Get the next frame pointer: */
if (state->next_bp) {
next_bp = state->next_bp;
state->next_bp = NULL;
} else if (state->regs) {
next_bp = (unsigned long *)state->regs->bp;
} else {
next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
}
/* Move to the next frame if it's safe: */
if (!update_stack_state(state, next_bp))
goto bad_address;
return true;
bad_address:
state->error = true;
/*
* When unwinding a non-current task, the task might actually be
* running on another CPU, in which case it could be modifying its
* stack while we're reading it. This is generally not a problem and
* can be ignored as long as the caller understands that unwinding
* another task will not always succeed.
*/
if (state->task != current)
goto the_end;
/*
* Don't warn if the unwinder got lost due to an interrupt in entry
* code or in the C handler before the first frame pointer got set up:
*/
if (state->got_irq && in_entry_code(state->ip))
goto the_end;
if (state->regs &&
state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
state->regs->sp < (unsigned long)task_pt_regs(state->task))
goto the_end;
/*
* There are some known frame pointer issues on 32-bit. Disable
* unwinder warnings on 32-bit until it gets objtool support.
*/
if (IS_ENABLED(CONFIG_X86_32))
goto the_end;
if (state->task != current)
goto the_end;
if (state->regs) {
printk_deferred_once(KERN_WARNING
"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
state->regs, state->task->comm,
state->task->pid, next_bp);
unwind_dump(state);
} else {
printk_deferred_once(KERN_WARNING
"WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
state->bp, state->task->comm,
state->task->pid, next_bp);
unwind_dump(state);
}
the_end:
state->stack_info.type = STACK_TYPE_UNKNOWN;
return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);
void __unwind_start(struct unwind_state *state, struct task_struct *task,
struct pt_regs *regs, unsigned long *first_frame)
{
unsigned long *bp;
memset(state, 0, sizeof(*state));
state->task = task;
state->got_irq = (regs);
/* Don't even attempt to start from user mode regs: */
if (regs && user_mode(regs)) {
state->stack_info.type = STACK_TYPE_UNKNOWN;
return;
}
bp = get_frame_pointer(task, regs);
/*
* If we crash with IP==0, the last successfully executed instruction
* was probably an indirect function call with a NULL function pointer.
* That means that SP points into the middle of an incomplete frame:
* *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
* would have written a frame pointer if we hadn't crashed.
* Pretend that the frame is complete and that BP points to it, but save
* the real BP so that we can use it when looking for the next frame.
*/
if (regs && regs->ip == 0 && (unsigned long *)regs->sp >= first_frame) {
state->next_bp = bp;
bp = ((unsigned long *)regs->sp) - 1;
}
/* Initialize stack info and make sure the frame data is accessible: */
get_stack_info(bp, state->task, &state->stack_info,
&state->stack_mask);
update_stack_state(state, bp);
/*
* The caller can provide the address of the first frame directly
* (first_frame) or indirectly (regs->sp) to indicate which stack frame
* to start unwinding at. Skip ahead until we reach it.
*/
while (!unwind_done(state) &&
(!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
(state->next_bp == NULL && state->bp < first_frame)))
unwind_next_frame(state);
}
EXPORT_SYMBOL_GPL(__unwind_start);
Codebase Browser
linux