[PATCH 2/2] s390x: Add 3f program exception handler

[Janosch Frank <frankja@linux.ibm.com>]

Program exception 3f (secure storage violation) can only be detected
when the CPU is running in SIE with a format 4 state description,
e.g. running a protected guest. Because of this and because user
space partly controls the guest memory mapping and can trigger this
exception, we want to send a SIGSEGV to the process running the guest
and not panic the kernel.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
CC: <stable@vger.kernel.org> # 5.7+
Fixes: 084ea4d611a3 ("s390/mm: add (non)secure page access exceptions handlers")
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kernel/pgm_check.S |  2 +-
 arch/s390/mm/fault.c         | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/pgm_check.S b/arch/s390/kernel/pgm_check.S
index 2c27907a5ffc..9a92638360ee 100644
--- a/arch/s390/kernel/pgm_check.S
+++ b/arch/s390/kernel/pgm_check.S
@@ -80,7 +80,7 @@ PGM_CHECK(do_dat_exception)		/* 3b */
 PGM_CHECK_DEFAULT			/* 3c */
 PGM_CHECK(do_secure_storage_access)	/* 3d */
 PGM_CHECK(do_non_secure_storage_access)	/* 3e */
-PGM_CHECK_DEFAULT			/* 3f */
+PGM_CHECK(do_secure_storage_violation)	/* 3f */
 PGM_CHECK(monitor_event_exception)	/* 40 */
 PGM_CHECK_DEFAULT			/* 41 */
 PGM_CHECK_DEFAULT			/* 42 */
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 4c8c063bce5b..20abb7c5c540 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -859,6 +859,24 @@ void do_non_secure_storage_access(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(do_non_secure_storage_access);
 
+void do_secure_storage_violation(struct pt_regs *regs)
+{
+	char buf[TASK_COMM_LEN];
+
+	/*
+	 * Either KVM messed up the secure guest mapping or the same
+	 * page is mapped into multiple secure guests.
+	 *
+	 * This exception is only triggered when a guest 2 is running
+	 * and can therefore never occur in kernel context.
+	 */
+	printk_ratelimited(KERN_WARNING
+			   "Secure storage violation in task: %s, pid %d\n",
+			   get_task_comm(buf, current), task_pid_nr(current));
+	send_sig(SIGSEGV, current, 0);
+}
+NOKPROBE_SYMBOL(do_secure_storage_violation);
+
 #else
 void do_secure_storage_access(struct pt_regs *regs)
 {
@@ -869,4 +887,9 @@ void do_non_secure_storage_access(struct pt_regs *regs)
 {
 	default_trap_handler(regs);
 }
+
+void do_secure_storage_violation(struct pt_regs *regs)
+{
+	default_trap_handler(regs);
+}
 #endif
-- 
2.25.1