1 files changed, 409 insertions, 0 deletions

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
new file mode 100644
index 000000000..d7c44b257
--- /dev/null
+++ b/arch/x86/kernel/unwind_frame.c
@@ -0,0 +1,409 @@
+// 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
+
+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 = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+						  addr, addr_p);
+	}
+
+	/* Save the original stack pointer for unwind_dump(): */
+	if (!state->orig_sp)
+		state->orig_sp = frame;
+
+	return true;
+}
+
+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);