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

Christian Borntraeger
2020-09-03T14:20:51Z

On 03.09.20 15:14, Janosch Frank wrote:
> 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>

I guess we will pick this up via the s390 tree?

> ---
> 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
>