From cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337 Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Fri, 15 Oct 2021 23:02:08 +1100
Subject: [PATCH] KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if
it went to guest
References: bko#206669 bsc#1174585 bsc#1192107 CVE-2021-43056
Patch-mainline: v5.15-rc6
Git-commit: cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337
We call idle_kvm_start_guest() from power7_offline() if the thread has
been requested to enter KVM. We pass it the SRR1 value that was returned
from power7_idle_insn() which tells us what sort of wakeup we're
processing.
Depending on the SRR1 value we pass in, the KVM code might enter the
guest, or it might return to us to do some host action if the wakeup
requires it.
If idle_kvm_start_guest() is able to handle the wakeup, and enter the
guest it is supposed to indicate that by returning a zero SRR1 value to
us.
That was the behaviour prior to commit 10d91611f426 ("powerpc/64s:
Reimplement book3s idle code in C"), however in that commit the
handling of SRR1 was reworked, and the zeroing behaviour was lost.
Returning from idle_kvm_start_guest() without zeroing the SRR1 value can
confuse the host offline code, causing the guest to crash and other
weirdness.
Fixes: 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015133929.832061-2-mpe@ellerman.id.au
Acked-by: Michal Suchanek <msuchanek@suse.de>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index ec57952b60b0..eb776d0c5d8e 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -264,6 +264,7 @@ _GLOBAL(idle_kvm_start_guest)
stdu r1, -SWITCH_FRAME_SIZE(r4)
// Switch to new frame on emergency stack
mr r1, r4
+ std r3, 32(r1) // Save SRR1 wakeup value
SAVE_NVGPRS(r1)
/*
@@ -315,6 +316,10 @@ kvm_unsplit_wakeup:
kvm_secondary_got_guest:
+ // About to go to guest, clear saved SRR1
+ li r0, 0
+ std r0, 32(r1)
+
/* Set HSTATE_DSCR(r13) to something sensible */
ld r6, PACA_DSCR_DEFAULT(r13)
std r6, HSTATE_DSCR(r13)
@@ -394,8 +399,8 @@ kvm_no_guest:
mfspr r4, SPRN_LPCR
rlwimi r4, r3, 0, LPCR_PECE0 | LPCR_PECE1
mtspr SPRN_LPCR, r4
- /* set up r3 for return */
- mfspr r3,SPRN_SRR1
+ // Return SRR1 wakeup value, or 0 if we went into the guest
+ ld r3, 32(r1)
REST_NVGPRS(r1)
ld r1, 0(r1) // Switch back to caller stack
ld r0, 16(r1) // Reload LR
--
2.31.1