Re: [PATCH 1/1] KVM: s390: Fix memory corruption by not reinjecting CK machine checks

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 06.08.26 um 16:37 schrieb Claudio Imbrenda:
> On Thu,  6 Aug 2026 14:52:41 +0200
> Christian Borntraeger <borntraeger@linux.ibm.com> wrote:
> 
>> Channel-subsystem damage machine checks are for the host channel
>> subsystem. The guest channel subsystem is emulated in the userspace VMM.
>> There is no point in forwarding such machine checks into the guest.
>>
>> This also simplifies the machine check reinjection and avoids kfree of a
>> stack variable as reported by sashiko.  There might be still machine
>> checks that have the ck bit set with another bit (like instruction
>> damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and
>> ED bits already are.
>>
>> Fixes: 4d62fcc0b692 ("KVM: s390: Inject machine check into the guest")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/nmi.h |  1 +
>>   arch/s390/kernel/nmi.c      |  4 ++--
>>   arch/s390/kvm/interrupt.c   | 24 ++++++++----------------
>>   3 files changed, 11 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/nmi.h b/arch/s390/include/asm/nmi.h
>> index 6454c1531854..dd26c20bd231 100644
>> --- a/arch/s390/include/asm/nmi.h
>> +++ b/arch/s390/include/asm/nmi.h
>> @@ -22,6 +22,7 @@
>>   #define MCCK_CODE_SYSTEM_DAMAGE		BIT(63)
>>   #define MCCK_CODE_EXT_DAMAGE		BIT(63 - 5)
>>   #define MCCK_CODE_CP			BIT(63 - 9)
>> +#define MCCK_CODE_CK			BIT(63 - 11)
>>   #define MCCK_CODE_STG_ERROR		BIT(63 - 16)
>>   #define MCCK_CODE_STG_KEY_ERROR		BIT(63 - 18)
>>   #define MCCK_CODE_STG_DEGRAD		BIT(63 - 19)
>> diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c
>> index e17a59d4d5a4..652b98795243 100644
>> --- a/arch/s390/kernel/nmi.c
>> +++ b/arch/s390/kernel/nmi.c
>> @@ -345,7 +345,7 @@ static void notrace s390_backup_mcck_info(struct pt_regs *regs)
>>   	sie_page = container_of(sie_block, struct sie_page, sie_block);
>>   	mcck_backup = &sie_page->mcck_info;
>>   	mcck_backup->mcic = get_lowcore()->mcck_interruption_code &
>> -				~(MCCK_CODE_CP | MCCK_CODE_EXT_DAMAGE);
>> +			~(MCCK_CODE_CP | MCCK_CODE_EXT_DAMAGE | MCCK_CODE_CK);
> 
> ... here, instead of duplicating it?
> 
>>   	mcck_backup->ext_damage_code = get_lowcore()->external_damage_code;
>>   	mcck_backup->failing_storage_address = get_lowcore()->failing_storage_address;
>>   }
>> @@ -357,7 +357,7 @@ NOKPROBE_SYMBOL(s390_backup_mcck_info);
>>   #define ED_STP_ISLAND	6	/* External damage STP island check */
>>   #define ED_STP_SYNC	7	/* External damage STP sync check */
>>   
>> -#define MCCK_CODE_NO_GUEST	(MCCK_CODE_CP | MCCK_CODE_EXT_DAMAGE)
>> +#define MCCK_CODE_NO_GUEST	(MCCK_CODE_CP | MCCK_CODE_EXT_DAMAGE | MCCK_CODE_CK)
> 
> it looks like this macro here should have been used above... ^

Yes, see my comment in the cover letter. We would need to move this define.