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#include <linux/sched.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)
{
unsigned long addr;
unsigned long *addr_p = unwind_get_return_address_ptr(state);
if (unwind_done(state))
return 0;
if (state->regs && user_mode(state->regs))
return 0;
addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p,
addr_p);
if (!__kernel_text_address(addr)) {
printk_deferred_once(KERN_WARNING
"WARNING: unrecognized kernel stack return address %p at %p in %s:%d\n",
(void *)addr, addr_p, state->task->comm,
state->task->pid);
return 0;
}
return addr;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
static size_t regs_size(struct pt_regs *regs)
{
/* x86_32 regs from kernel mode are two words shorter: */
if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
return sizeof(*regs) - 2*sizeof(long);
return sizeof(*regs);
}
static bool is_last_task_frame(struct unwind_state *state)
{
unsigned long bp = (unsigned long)state->bp;
unsigned long regs = (unsigned long)task_pt_regs(state->task);
return bp == regs - FRAME_HEADER_SIZE;
}
/*
* This determines if the frame pointer actually contains an encoded pointer to
* pt_regs on the stack. See ENCODE_FRAME_POINTER.
*/
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);
}
static bool update_stack_state(struct unwind_state *state, void *addr,
size_t len)
{
struct stack_info *info = &state->stack_info;
/*
* If addr 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 'addr' could
* be on a subsequent stack.
*/
while (!on_stack(info, addr, len))
if (get_stack_info(info->next_sp, state->task, info,
&state->stack_mask))
return false;
return true;
}
bool unwind_next_frame(struct unwind_state *state)
{
struct pt_regs *regs;
unsigned long *next_bp, *next_frame;
size_t next_len;
enum stack_type prev_type = state->stack_info.type;
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_tls(). 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
* do_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;
return true;
}
/* get the next frame pointer */
if (state->regs)
next_bp = (unsigned long *)state->regs->bp;
else
next_bp = (unsigned long *)*state->bp;
/* is the next frame pointer an encoded pointer to pt_regs? */
regs = decode_frame_pointer(next_bp);
if (regs) {
next_frame = (unsigned long *)regs;
next_len = sizeof(*regs);
} else {
next_frame = next_bp;
next_len = FRAME_HEADER_SIZE;
}
/* make sure the next frame's data is accessible */
if (!update_stack_state(state, next_frame, next_len)) {
/*
* Don't warn on bad regs->bp. An interrupt in entry code
* might cause a false positive warning.
*/
if (state->regs)
goto the_end;
goto bad_address;
}
/* Make sure it only unwinds up and doesn't overlap the last frame: */
if (state->stack_info.type == prev_type) {
if (state->regs && (void *)next_frame < (void *)state->regs + regs_size(state->regs))
goto bad_address;
if (state->bp && (void *)next_frame < (void *)state->bp + FRAME_HEADER_SIZE)
goto bad_address;
}
/* move to the next frame */
if (regs) {
state->regs = regs;
state->bp = NULL;
} else {
state->bp = next_bp;
state->regs = NULL;
}
return true;
bad_address:
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_frame);
} 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_frame);
}
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, *frame;
size_t len;
memset(state, 0, sizeof(*state));
state->task = task;
/* don't even attempt to start from user mode regs */
if (regs && user_mode(regs)) {
state->stack_info.type = STACK_TYPE_UNKNOWN;
return;
}
/* set up the starting stack frame */
bp = get_frame_pointer(task, regs);
regs = decode_frame_pointer(bp);
if (regs) {
state->regs = regs;
frame = (unsigned long *)regs;
len = sizeof(*regs);
} else {
state->bp = bp;
frame = bp;
len = FRAME_HEADER_SIZE;
}
/* initialize stack info and make sure the frame data is accessible */
get_stack_info(frame, state->task, &state->stack_info,
&state->stack_mask);
update_stack_state(state, frame, len);
/*
* 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->bp < first_frame))
unwind_next_frame(state);
}
EXPORT_SYMBOL_GPL(__unwind_start);
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