Commit 29ccaa4b authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Heiko Carstens
Browse files

s390/mcck: isolate SIE instruction when setting CIF_MCCK_GUEST flag 



Commit d768bd89 ("s390: add options to change branch prediction
behaviour for the kernel") introduced .Lsie_exit label - supposedly
to fence off SIE instruction. However, the corresponding address
range length .Lsie_crit_mcck_length was not updated, which led to
BPON code potentionally marked with CIF_MCCK_GUEST flag.

Both .Lsie_exit and .Lsie_crit_mcck_length were removed with commit
0b0ed657 ("s390: remove critical section cleanup from entry.S"),
but the issue persisted - currently BPOFF and BPENTER macros might
get wrongly considered by the machine check handler as a guest.

Fixes: d768bd89 ("s390: add options to change branch prediction behaviour for the kernel")
Reviewed-by: default avatarSven Schnelle <svens@linux.ibm.com>
Reviewed-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 3ae11dbc

arch/s390/kernel/entry.S

+5 −1
Original line number Diff line number Diff line
@@ -251,6 +251,10 @@ ENTRY(sie64a) 
	BPEXIT	__SF_SIE_FLAGS(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)

.Lsie_entry:

	sie	0(%r14)

# Let the next instruction be NOP to avoid triggering a machine check

# and handling it in a guest as result of the instruction execution.

	nopr	7

.Lsie_leave:

	BPOFF

	BPENTER	__SF_SIE_FLAGS(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)

.Lsie_skip:
@@ -547,7 +551,7 @@ ENTRY(mcck_int_handler) 
	jno	.Lmcck_panic

#if IS_ENABLED(CONFIG_KVM)

	OUTSIDE	%r9,.Lsie_gmap,.Lsie_done,6f

	OUTSIDE	%r9,.Lsie_entry,.Lsie_skip,4f

	OUTSIDE	%r9,.Lsie_entry,.Lsie_leave,4f

	oi	__LC_CPU_FLAGS+7, _CIF_MCCK_GUEST

	j	5f

4:	CHKSTG	.Lmcck_panic