[PATCH v2 2/2] s390x: Add 3f program exception handler

Janosch Frank
2020-09-07T12:47:29Z

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>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
arch/s390/kernel/pgm_check.S | 2 +-
arch/s390/mm/fault.c | 20 ++++++++++++++++++++
2 files changed, 21 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..996884dcc9fd 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -859,6 +859,21 @@ 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)
+{
+ /*
+ * 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",
+ current->comm, current->pid);
+ send_sig(SIGSEGV, current, 0);
+}
+
#else
void do_secure_storage_access(struct pt_regs *regs)
{
@@ -869,4 +884,9 @@ 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