From cf13435b730a502e814c63c84d93db131e563f5f Mon Sep 17 00:00:00 2001
From: Michael Neuling <mikey@neuling.org>
Date: Mon, 24 Sep 2018 17:27:04 +1000
Subject: [PATCH] powerpc/tm: Fix userspace r13 corruption
References: bsc#1109333
Patch-mainline: v4.19-rc6
Git-commit: cf13435b730a502e814c63c84d93db131e563f5f
When we treclaim we store the userspace checkpointed r13 to a scratch
SPR and then later save the scratch SPR to the user thread struct.
Unfortunately, this doesn't work as accessing the user thread struct
can take an SLB fault and the SLB fault handler will write the same
scratch SPRG that now contains the userspace r13.
To fix this, we store r13 to the kernel stack (which can't fault)
before we access the user thread struct.
Found by running P8 guest + powervm + disable_1tb_segments + TM. Seen
as a random userspace segfault with r13 looking like a kernel address.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/tm.S | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/tm.S b/arch/powerpc/kernel/tm.S
index 6bffbc5affe7..183e8d75936f 100644
--- a/arch/powerpc/kernel/tm.S
+++ b/arch/powerpc/kernel/tm.S
@@ -176,13 +176,20 @@ _GLOBAL(tm_reclaim)
std r1, PACATMSCRATCH(r13)
ld r1, PACAR1(r13)
- /* Store the PPR in r11 and reset to decent value */
std r11, GPR11(r1) /* Temporary stash */
+ /*
+ * Store r13 away so we can free up the scratch SPR for the SLB fault
+ * handler (needed once we start accessing the thread_struct).
+ */
+ GET_SCRATCH0(r11)
+ std r11, GPR13(r1)
+
/* Reset MSR RI so we can take SLB faults again */
li r11, MSR_RI
mtmsrd r11, 1
+ /* Store the PPR in r11 and reset to decent value */
mfspr r11, SPRN_PPR
HMT_MEDIUM
@@ -211,7 +218,7 @@ _GLOBAL(tm_reclaim)
ld r4, GPR7(r1) /* user r7 */
ld r5, GPR11(r1) /* user r11 */
ld r6, GPR12(r1) /* user r12 */
- GET_SCRATCH0(8) /* user r13 */
+ ld r8, GPR13(r1) /* user r13 */
std r3, GPR1(r7)
std r4, GPR7(r7)
std r5, GPR11(r7)
--
2.13.7