[PATCH 4.4 50/50] s390/uprobes: implement arch_uretprobe_is_alive()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>

commit 783c3b53b9506db3e05daacfe34e0287eebb09d8 upstream.

Implement s390 specific arch_uretprobe_is_alive() to avoid SIGSEGVs
observed with uretprobes in combination with setjmp/longjmp.

See commit 2dea1d9c38e4 ("powerpc/uprobes: Implement
arch_uretprobe_is_alive()") for more details.

With this implemented all test cases referenced in the above commit
pass.

Reported-by: Ziqian SUN <zsun@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.3+
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/s390/kernel/uprobes.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/s390/kernel/uprobes.c
+++ b/arch/s390/kernel/uprobes.c
@@ -147,6 +147,15 @@ unsigned long arch_uretprobe_hijack_retu
 	return orig;
 }
 
+bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
+			     struct pt_regs *regs)
+{
+	if (ctx == RP_CHECK_CHAIN_CALL)
+		return user_stack_pointer(regs) <= ret->stack;
+	else
+		return user_stack_pointer(regs) < ret->stack;
+}
+
 /* Instruction Emulation */
 
 static void adjust_psw_addr(psw_t *psw, unsigned long len)