[RFC PATCH v1 13/16] s390/unwind_user/backchain: Enable HAVE_UNWIND_USER_BACKCHAIN

[Jens Remus <jremus@linux.ibm.com>]

Enable unwinding of user space using back chain on s390.  Based on
arch_stack_walk_user_common() in arch/s390/kernel/stacktrace.c.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 arch/s390/Kconfig                             |   1 +
 arch/s390/include/asm/unwind_user_backchain.h | 127 ++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 arch/s390/include/asm/unwind_user_backchain.h

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 8b29a8f0f9c3..49f231123040 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -239,6 +239,7 @@ config S390
 	select HAVE_SETUP_PER_CPU_AREA
 	select HAVE_SOFTIRQ_ON_OWN_STACK
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_UNWIND_USER_BACKCHAIN
 	select HAVE_UNWIND_USER_LOC_REG
 	select HAVE_UNWIND_USER_SFRAME
 	select HAVE_USER_RA_REG
diff --git a/arch/s390/include/asm/unwind_user_backchain.h b/arch/s390/include/asm/unwind_user_backchain.h
new file mode 100644
index 000000000000..ceb56b9d8411
--- /dev/null
+++ b/arch/s390/include/asm/unwind_user_backchain.h
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_UNWIND_USER_BACKCHAIN_H
+#define _ASM_S390_UNWIND_USER_BACKCHAIN_H
+
+#include <linux/security.h>
+#ifndef ASM_OFFSETS_C
+#include <asm/asm-offsets.h>
+#endif
+
+struct stack_frame_user {
+	unsigned long backchain;
+	unsigned long unused;
+	/* Argument register save area. */
+	unsigned long r2;
+	unsigned long r3;
+	unsigned long r4;
+	unsigned long r5;
+	unsigned long r6;
+	/* Other register save area. */
+	unsigned long r7;
+	unsigned long r8;
+	unsigned long r9;
+	unsigned long r10;
+	unsigned long r11;
+	unsigned long r12;
+	unsigned long r13;
+	unsigned long r14;
+	unsigned long r15;
+	/* FP argument register save area. */
+	unsigned long f0;
+	unsigned long f2;
+	unsigned long f4;
+	unsigned long f6;
+};
+
+struct stack_frame_vdso_wrapper {
+	struct stack_frame_user sf;
+	unsigned long return_address;
+};
+
+/**
+ * ip_invalid - Perform some basic checks whether an instruction pointer (IP)
+ * taken from an unreliable source is invalid
+ * @ip: The instruction pointer to be validated
+ *
+ * returns whether the instruction pointer is invalid
+ */
+static inline bool ip_invalid(unsigned long ip)
+{
+	if (ip & 1)
+		return true;
+	if (ip < mmap_min_addr)
+		return true;
+	if (ip >= current->mm->context.asce_limit)
+		return true;
+	return false;
+}
+
+/**
+ * ip_within_vdso - Check whether an instruction pointer (IP) is within vDSO
+ * @ip: The instruction pointer
+ *
+ * returns whether the instruction pointer is within vDSO
+ */
+static inline bool ip_within_vdso(unsigned long ip)
+{
+	return in_range(ip, current->mm->context.vdso_base, vdso_text_size());
+}
+
+/**
+ * arch_unwind_user_backchain_next - Unwind one frame using backchain
+ * @state: The unwind user state
+ *
+ * returns zero when successful, otherwise -EINVAL.
+ */
+static inline int arch_unwind_user_backchain_next(struct unwind_user_state *state)
+{
+	struct stack_frame_user __user *sf;
+	unsigned long sp, ra;
+
+	sf = (void __user *)state->sp;
+	if (__get_user(sp, (unsigned long __user *)&sf->backchain))
+		return -EINVAL;
+
+	/*
+	 * vDSO entry code on s390 has a non-standard stack frame layout.
+	 * See vDSO user wrapper code for details.
+	 */
+	if (!sp && ip_within_vdso(state->ip)) {
+		struct stack_frame_vdso_wrapper *sf_vdso = (void __user *)sf;
+
+		if (__get_user(ra, (unsigned long __user *)&sf_vdso->return_address))
+			return -EINVAL;
+		sf = (void __user *)((unsigned long)sf + STACK_FRAME_VDSO_OVERHEAD);
+		if (__get_user(sp, (unsigned long __user *)&sf->backchain))
+			return -EINVAL;
+	} else {
+		sf = (void __user *)sp;
+		if (__get_user(ra, (unsigned long __user *)&sf->r14))
+			return -EINVAL;
+	}
+
+	/* ABI requires SP to be 8-byte aligned. */
+	if (sp & 0x7)
+		return -EINVAL;
+
+	/*
+	 * If the IP is invalid and this is the topmost frame,
+	 * assume the RA register has not been saved yet.
+	 */
+	if (ip_invalid(ra)) {
+		if (!state->topmost || !IS_ENABLED(CONFIG_HAVE_USER_RA_REG))
+			return -EINVAL;
+
+		ra = user_return_address(task_pt_regs(current));
+		if (ip_invalid(ra))
+			return -EINVAL;
+	}
+
+	state->sp = sp;
+	state->ip = ra;
+	state->fp = 0;
+
+	return 0;
+}
+
+#endif /* _ASM_S390_UNWIND_USER_BACKCHAIN_H */
-- 
2.48.1