Add optional support for user space compat mode frame pointer unwinding.
If supported, the arch needs to enable CONFIG_HAVE_UNWIND_USER_COMPAT_FP
and define ARCH_INIT_USER_COMPAT_FP_FRAME.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/Kconfig                            |  4 +++
 include/asm-generic/Kbuild              |  2 ++
 include/asm-generic/unwind_user.h       | 15 +++++++++++
 include/asm-generic/unwind_user_types.h |  9 +++++++
 include/linux/unwind_user_types.h       |  3 +++
 kernel/unwind/user.c                    | 36 ++++++++++++++++++++++---
 6 files changed, 65 insertions(+), 4 deletions(-)
 create mode 100644 include/asm-generic/unwind_user_types.h

diff --git a/arch/Kconfig b/arch/Kconfig
index cf996cbb8142..f1f7a3857c97 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -442,6 +442,10 @@ config HAVE_UNWIND_USER_FP
 	bool
 	select UNWIND_USER
 
+config HAVE_UNWIND_USER_COMPAT_FP
+	bool
+	depends on HAVE_UNWIND_USER_FP
+
 config AS_SFRAME
 	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
 
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 1b43c3a77012..2f3e4e2d8610 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -58,6 +58,8 @@ mandatory-y += tlbflush.h
 mandatory-y += topology.h
 mandatory-y += trace_clock.h
 mandatory-y += uaccess.h
+mandatory-y += unwind_user.h
+mandatory-y += unwind_user_types.h
 mandatory-y += vermagic.h
 mandatory-y += vga.h
 mandatory-y += video.h
diff --git a/include/asm-generic/unwind_user.h b/include/asm-generic/unwind_user.h
index 832425502fb3..385638ce4aec 100644
--- a/include/asm-generic/unwind_user.h
+++ b/include/asm-generic/unwind_user.h
@@ -2,8 +2,23 @@
 #ifndef _ASM_GENERIC_UNWIND_USER_H
 #define _ASM_GENERIC_UNWIND_USER_H
 
+#include <asm/unwind_user_types.h>
+
 #ifndef ARCH_INIT_USER_FP_FRAME
  #define ARCH_INIT_USER_FP_FRAME
 #endif
 
+#ifndef ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define in_compat_mode(regs) false
+#endif
+
+#ifndef arch_unwind_user_init
+static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
+#endif
+
+#ifndef arch_unwind_user_next
+static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
+#endif
+
 #endif /* _ASM_GENERIC_UNWIND_USER_H */
diff --git a/include/asm-generic/unwind_user_types.h b/include/asm-generic/unwind_user_types.h
new file mode 100644
index 000000000000..ee803de7c998
--- /dev/null
+++ b/include/asm-generic/unwind_user_types.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_UNWIND_USER_TYPES_H
+#define _ASM_GENERIC_UNWIND_USER_TYPES_H
+
+#ifndef arch_unwind_user_state
+struct arch_unwind_user_state {};
+#endif
+
+#endif /* _ASM_GENERIC_UNWIND_USER_TYPES_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 65bd070eb6b0..3ec4a097a3dd 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -3,10 +3,12 @@
 #define _LINUX_UNWIND_USER_TYPES_H
 
 #include <linux/types.h>
+#include <asm/unwind_user_types.h>
 
 enum unwind_user_type {
 	UNWIND_USER_TYPE_NONE,
 	UNWIND_USER_TYPE_FP,
+	UNWIND_USER_TYPE_COMPAT_FP,
 };
 
 struct unwind_stacktrace {
@@ -25,6 +27,7 @@ struct unwind_user_state {
 	unsigned long ip;
 	unsigned long sp;
 	unsigned long fp;
+	struct arch_unwind_user_state arch;
 	enum unwind_user_type type;
 	bool done;
 };
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 73fd4e150dfd..92963f129c6a 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -13,12 +13,32 @@ static struct unwind_user_frame fp_frame = {
 	ARCH_INIT_USER_FP_FRAME
 };
 
+static struct unwind_user_frame compat_fp_frame = {
+	ARCH_INIT_USER_COMPAT_FP_FRAME
+};
+
 static inline bool fp_state(struct unwind_user_state *state)
 {
 	return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
 	       state->type == UNWIND_USER_TYPE_FP;
 }
 
+static inline bool compat_state(struct unwind_user_state *state)
+{
+	return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) &&
+	       state->type == UNWIND_USER_TYPE_COMPAT_FP;
+}
+
+#define UNWIND_GET_USER_LONG(to, from, state)				\
+({									\
+	int __ret;							\
+	if (compat_state(state))					\
+		__ret = get_user(to, (u32 __user *)(from));		\
+	else								\
+		__ret = get_user(to, (u64 __user *)(from));		\
+	__ret;								\
+})
+
 int unwind_user_next(struct unwind_user_state *state)
 {
 	struct unwind_user_frame _frame;
@@ -28,7 +48,9 @@ int unwind_user_next(struct unwind_user_state *state)
 	if (state->done)
 		return -EINVAL;
 
-	if (fp_state(state))
+	if (compat_state(state))
+		frame = &compat_fp_frame;
+	else if (fp_state(state))
 		frame = &fp_frame;
 	else
 		goto the_end;
@@ -39,10 +61,10 @@ int unwind_user_next(struct unwind_user_state *state)
 	if (cfa <= state->sp)
 		goto the_end;
 
-	if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+	if (UNWIND_GET_USER_LONG(ra, cfa + frame->ra_off, state))
 		goto the_end;
 
-	if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
+	if (frame->fp_off && UNWIND_GET_USER_LONG(fp, cfa + frame->fp_off, state))
 		goto the_end;
 
 	state->ip = ra;
@@ -50,6 +72,8 @@ int unwind_user_next(struct unwind_user_state *state)
 	if (frame->fp_off)
 		state->fp = fp;
 
+	arch_unwind_user_next(state);
+
 	return 0;
 
 the_end:
@@ -68,7 +92,9 @@ int unwind_user_start(struct unwind_user_state *state)
 		return -EINVAL;
 	}
 
-	if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
+	if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) && in_compat_mode(regs))
+		state->type = UNWIND_USER_TYPE_COMPAT_FP;
+	else if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
 		state->type = UNWIND_USER_TYPE_FP;
 	else
 		state->type = UNWIND_USER_TYPE_NONE;
@@ -77,6 +103,8 @@ int unwind_user_start(struct unwind_user_state *state)
 	state->sp = user_stack_pointer(regs);
 	state->fp = frame_pointer(regs);
 
+	arch_unwind_user_init(state, regs);
+
 	return 0;
 }
 
-- 
2.48.1