[PATCH v11 14/14] unwind_user/x86: Enable compat mode frame pointer unwinding on x86

[Steven Rostedt <rostedt@goodmis.org>]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Use ARCH_INIT_USER_COMPAT_FP_FRAME to describe how frame pointers are
unwound on x86, and implement the hooks needed to add the segment base
addresses.  Enable HAVE_UNWIND_USER_COMPAT_FP if the system has compat
mode compiled in.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v10: https://lore.kernel.org/20250611010430.123232579@goodmis.org

- Moved calling the functions arch_unwind_user_init() and
  arch_unwind_user_next() to this commit as it's the first commit to use
  them. (Peter Zijlstra)

 arch/x86/Kconfig                         |  1 +
 arch/x86/include/asm/unwind_user.h       | 49 ++++++++++++++++++++++++
 arch/x86/include/asm/unwind_user_types.h | 17 ++++++++
 include/linux/unwind_user.h              | 20 ++++++++++
 kernel/unwind/user.c                     |  4 ++
 5 files changed, 91 insertions(+)
 create mode 100644 arch/x86/include/asm/unwind_user_types.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2cdb5cf91541..3f7bdc9e3cec 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -302,6 +302,7 @@ config X86
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
+	select HAVE_UNWIND_USER_COMPAT_FP	if IA32_EMULATION
 	select HAVE_UNWIND_USER_FP		if X86_64
 	select HAVE_USER_RETURN_NOTIFIER
 	select HAVE_GENERIC_VDSO
diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 8597857bf896..43f8554c1d70 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -2,10 +2,59 @@
 #ifndef _ASM_X86_UNWIND_USER_H
 #define _ASM_X86_UNWIND_USER_H
 
+#include <linux/unwind_user_types.h>
+#include <asm/ptrace.h>
+
 #define ARCH_INIT_USER_FP_FRAME							\
 	.cfa_off	= (s32)sizeof(long) *  2,				\
 	.ra_off		= (s32)sizeof(long) * -1,				\
 	.fp_off		= (s32)sizeof(long) * -2,				\
 	.use_fp		= true,
 
+#ifdef CONFIG_IA32_EMULATION
+
+#define ARCH_INIT_USER_COMPAT_FP_FRAME						\
+	.cfa_off	= (s32)sizeof(u32)  *  2,				\
+	.ra_off		= (s32)sizeof(u32)  * -1,				\
+	.fp_off		= (s32)sizeof(u32)  * -2,				\
+	.use_fp		= true,
+
+#define in_compat_mode(regs) !user_64bit_mode(regs)
+
+static inline void arch_unwind_user_init(struct unwind_user_state *state,
+					 struct pt_regs *regs)
+{
+	unsigned long cs_base, ss_base;
+
+	if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+		return;
+
+	scoped_guard(irqsave) {
+		cs_base = segment_base_address(regs->cs);
+		ss_base = segment_base_address(regs->ss);
+	}
+
+	state->arch.cs_base = cs_base;
+	state->arch.ss_base = ss_base;
+
+	state->ip += cs_base;
+	state->sp += ss_base;
+	state->fp += ss_base;
+}
+#define arch_unwind_user_init arch_unwind_user_init
+
+static inline void arch_unwind_user_next(struct unwind_user_state *state)
+{
+	if (state->type != UNWIND_USER_TYPE_COMPAT_FP)
+		return;
+
+	state->ip += state->arch.cs_base;
+	state->fp += state->arch.ss_base;
+}
+#define arch_unwind_user_next arch_unwind_user_next
+
+#endif /* CONFIG_IA32_EMULATION */
+
+#include <asm-generic/unwind_user.h>
+
 #endif /* _ASM_X86_UNWIND_USER_H */
diff --git a/arch/x86/include/asm/unwind_user_types.h b/arch/x86/include/asm/unwind_user_types.h
new file mode 100644
index 000000000000..d7074dc5f0ce
--- /dev/null
+++ b/arch/x86/include/asm/unwind_user_types.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UNWIND_USER_TYPES_H
+#define _ASM_UNWIND_USER_TYPES_H
+
+#ifdef CONFIG_IA32_EMULATION
+
+struct arch_unwind_user_state {
+	unsigned long ss_base;
+	unsigned long cs_base;
+};
+#define arch_unwind_user_state arch_unwind_user_state
+
+#endif /* CONFIG_IA32_EMULATION */
+
+#include <asm-generic/unwind_user_types.h>
+
+#endif /* _ASM_UNWIND_USER_TYPES_H */
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index ac007363820a..46f995cda606 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -14,6 +14,26 @@
  #define in_compat_mode(regs) false
 #endif
 
+/*
+ * If an architecture needs to initialize the state for a specific
+ * reason, for example, it may need to do something different
+ * in compat mode, it can define arch_unwind_user_init to a
+ * function that will perform this initialization.
+ */
+#ifndef arch_unwind_user_init
+static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
+#endif
+
+/*
+ * If an architecture requires some more updates to the state between
+ * stack frames, it can define arch_unwind_user_next to a function
+ * that will update the state between reading stack frames during
+ * the user space stack walk.
+ */
+#ifndef arch_unwind_user_next
+static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
+#endif
+
 int unwind_user_start(struct unwind_user_state *state);
 int unwind_user_next(struct unwind_user_state *state);
 
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 3a0ac4346f5b..2bb7995c3f23 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -72,6 +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;
 
 done:
@@ -101,6 +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;
 }
 
-- 
2.47.2