s390/ftrace: fix arch_ftrace_get_regs implementation

arch_ftrace_get_regs is supposed to return a struct pt_regs pointer
only if the pt_regs structure contains all register contents, which
means it must have been populated when created via ftrace_regs_caller.

If it was populated via ftrace_caller the contents are not complete
(the psw mask part is missing), and therefore a NULL pointer needs be
returned.

The current code incorrectly always returns a struct pt_regs pointer.

Fix this by adding another pt_regs flag which indicates if the
contents are complete, and fix arch_ftrace_get_regs accordingly.

Fixes: 8949796 ("s390/ftrace: provide separate ftrace_caller/ftrace_regs_caller implementations")
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reported-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/ftrace.h

@@ -47,15 +47,17 @@ struct ftrace_regs {
 
 static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *fregs)
 {
-	return &fregs->regs;
+	struct pt_regs *regs = &fregs->regs;
+
+	if (test_pt_regs_flag(regs, PIF_FTRACE_FULL_REGS))
+		return regs;
+	return NULL;
 }
 
 static __always_inline void ftrace_instruction_pointer_set(struct ftrace_regs *fregs,
 							   unsigned long ip)
 {
-	struct pt_regs *regs = arch_ftrace_get_regs(fregs);
-
-	regs->psw.addr = ip;
+	fregs->regs.psw.addr = ip;
 }
 
 /*

arch/s390/include/asm/ptrace.h

@@ -15,11 +15,13 @@
 #define PIF_EXECVE_PGSTE_RESTART	1	/* restart execve for PGSTE binaries */
 #define PIF_SYSCALL_RET_SET		2	/* return value was set via ptrace */
 #define PIF_GUEST_FAULT			3	/* indicates program check in sie64a */
+#define PIF_FTRACE_FULL_REGS		4	/* all register contents valid (ftrace) */
 
 #define _PIF_SYSCALL			BIT(PIF_SYSCALL)
 #define _PIF_EXECVE_PGSTE_RESTART	BIT(PIF_EXECVE_PGSTE_RESTART)
 #define _PIF_SYSCALL_RET_SET		BIT(PIF_SYSCALL_RET_SET)
 #define _PIF_GUEST_FAULT		BIT(PIF_GUEST_FAULT)
+#define _PIF_FTRACE_FULL_REGS		BIT(PIF_FTRACE_FULL_REGS)
 
 #ifndef __ASSEMBLY__
 

arch/s390/kernel/ftrace.c

@@ -326,7 +326,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 
 	regs = ftrace_get_regs(fregs);
 	p = get_kprobe((kprobe_opcode_t *)ip);
-	if (unlikely(!p) || kprobe_disabled(p))
+	if (!regs || unlikely(!p) || kprobe_disabled(p))
 		goto out;
 
 	if (kprobe_running()) {

arch/s390/kernel/mcount.S

@@ -27,6 +27,7 @@ ENDPROC(ftrace_stub)
 #define STACK_PTREGS_GPRS	(STACK_PTREGS + __PT_GPRS)
 #define STACK_PTREGS_PSW	(STACK_PTREGS + __PT_PSW)
 #define STACK_PTREGS_ORIG_GPR2	(STACK_PTREGS + __PT_ORIG_GPR2)
+#define STACK_PTREGS_FLAGS	(STACK_PTREGS + __PT_FLAGS)
 #ifdef __PACK_STACK
 /* allocate just enough for r14, r15 and backchain */
 #define TRACED_FUNC_FRAME_SIZE	24
@@ -57,6 +58,14 @@ ENDPROC(ftrace_stub)
 	.if \allregs == 1
 	stg	%r14,(STACK_PTREGS_PSW)(%r15)
 	stosm	(STACK_PTREGS_PSW)(%r15),0
+#ifdef CONFIG_HAVE_MARCH_Z10_FEATURES
+	mvghi	STACK_PTREGS_FLAGS(%r15),_PIF_FTRACE_FULL_REGS
+#else
+	lghi	%r14,_PIF_FTRACE_FULL_REGS
+	stg	%r14,STACK_PTREGS_FLAGS(%r15)
+#endif
+	.else
+	xc	STACK_PTREGS_FLAGS(8,%r15),STACK_PTREGS_FLAGS(%r15)
 	.endif
 
 	lg	%r14,(__SF_GPRS+8*8)(%r1)	# restore original return address