Introduce a generic API for unwinding user stacks.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/Kconfig                      |  3 ++
 include/linux/unwind_user.h       | 15 ++++++++
 include/linux/unwind_user_types.h | 31 ++++++++++++++++
 kernel/Makefile                   |  1 +
 kernel/unwind/Makefile            |  1 +
 kernel/unwind/user.c              | 59 +++++++++++++++++++++++++++++++
 6 files changed, 110 insertions(+)
 create mode 100644 include/linux/unwind_user.h
 create mode 100644 include/linux/unwind_user_types.h
 create mode 100644 kernel/unwind/Makefile
 create mode 100644 kernel/unwind/user.c

diff --git a/arch/Kconfig b/arch/Kconfig
index 65228c78fef0..c6fa2b3ecbc6 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -435,6 +435,9 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
 	  It uses the same command line parameters, and sysctl interface,
 	  as the generic hardlockup detectors.
 
+config UNWIND_USER
+	bool
+
 config AS_SFRAME
 	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
 
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
new file mode 100644
index 000000000000..aa7923c1384f
--- /dev/null
+++ b/include/linux/unwind_user.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UNWIND_USER_H
+#define _LINUX_UNWIND_USER_H
+
+#include <linux/unwind_user_types.h>
+
+int unwind_user_start(struct unwind_user_state *state);
+int unwind_user_next(struct unwind_user_state *state);
+
+int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
+
+#define for_each_user_frame(state) \
+	for (unwind_user_start((state)); !(state)->done; unwind_user_next((state)))
+
+#endif /* _LINUX_UNWIND_USER_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
new file mode 100644
index 000000000000..6ed1b4ae74e1
--- /dev/null
+++ b/include/linux/unwind_user_types.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UNWIND_USER_TYPES_H
+#define _LINUX_UNWIND_USER_TYPES_H
+
+#include <linux/types.h>
+
+enum unwind_user_type {
+	UNWIND_USER_TYPE_NONE,
+};
+
+struct unwind_stacktrace {
+	unsigned int	nr;
+	unsigned long	*entries;
+};
+
+struct unwind_user_frame {
+	s32 cfa_off;
+	s32 ra_off;
+	s32 fp_off;
+	bool use_fp;
+};
+
+struct unwind_user_state {
+	unsigned long ip;
+	unsigned long sp;
+	unsigned long fp;
+	enum unwind_user_type type;
+	bool done;
+};
+
+#endif /* _LINUX_UNWIND_USER_TYPES_H */
diff --git a/kernel/Makefile b/kernel/Makefile
index 87866b037fbe..6cb4b0e02a34 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -50,6 +50,7 @@ obj-y += rcu/
 obj-y += livepatch/
 obj-y += dma/
 obj-y += entry/
+obj-y += unwind/
 obj-$(CONFIG_MODULES) += module/
 
 obj-$(CONFIG_KCMP) += kcmp.o
diff --git a/kernel/unwind/Makefile b/kernel/unwind/Makefile
new file mode 100644
index 000000000000..349ce3677526
--- /dev/null
+++ b/kernel/unwind/Makefile
@@ -0,0 +1 @@
+ obj-$(CONFIG_UNWIND_USER) += user.o
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
new file mode 100644
index 000000000000..456539635e49
--- /dev/null
+++ b/kernel/unwind/user.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+* Generic interfaces for unwinding user space
+*/
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/unwind_user.h>
+
+int unwind_user_next(struct unwind_user_state *state)
+{
+	struct unwind_user_frame _frame;
+	struct unwind_user_frame *frame = &_frame;
+	unsigned long cfa = 0, fp, ra = 0;
+
+	/* no implementation yet */
+	-EINVAL;
+}
+
+int unwind_user_start(struct unwind_user_state *state)
+{
+	struct pt_regs *regs = task_pt_regs(current);
+
+	memset(state, 0, sizeof(*state));
+
+	if (!current->mm || !user_mode(regs)) {
+		state->done = true;
+		return -EINVAL;
+	}
+
+	state->type = UNWIND_USER_TYPE_NONE;
+
+	state->ip = instruction_pointer(regs);
+	state->sp = user_stack_pointer(regs);
+	state->fp = frame_pointer(regs);
+
+	return 0;
+}
+
+int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries)
+{
+	struct unwind_user_state state;
+
+	trace->nr = 0;
+
+	if (!max_entries)
+		return -EINVAL;
+
+	if (!current->mm)
+		return 0;
+
+	for_each_user_frame(&state) {
+		trace->entries[trace->nr++] = state.ip;
+		if (trace->nr >= max_entries)
+			break;
+	}
+
+	return 0;
+}
-- 
2.48.1