This is a note to let you know that I've just added the patch titled
s390/mcck: isolate SIE instruction when setting CIF_MCCK_GUEST flag
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
s390-mcck-isolate-sie-instruction-when-setting-cif_m.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a7ee291ae3c523ac2f8897f110dea833ccf08df4
Author: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Date: Mon May 23 12:38:14 2022 +0200
s390/mcck: isolate SIE instruction when setting CIF_MCCK_GUEST flag
[ Upstream commit 29ccaa4b35ea874ddd50518e5c2c746b9238a792 ]
Commit d768bd892fc8 ("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
0b0ed657fe00 ("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: d768bd892fc8 ("s390: add options to change branch prediction behaviour for the kernel")
Reviewed-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 4c9b967290ae..d530eb4dc413 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -248,6 +248,10 @@ 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:
@@ -536,7 +540,7 @@ 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
