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s390/mcck: isolate SIE instruction when setting CIF_MCCK_GUEST flag 

Commit d768bd892f ("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
0b0ed657fe ("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: d768bd892f ("s390: add options to change branch prediction behaviour for the kernel")
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Alexander Gordeev 2022-05-23 12:38:14 +02:00 committed by Heiko Carstens
parent 3ae11dbcfa
commit 29ccaa4b35
1 changed files with 5 additions and 1 deletions
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6
arch/s390/kernel/entry.S
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@ -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