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Subject[PATCH 4.19 097/190] powerpc/kvm: Save and restore host AMR/IAMR/UAMOR
[ Upstream commit c3c7470c75566a077c8dc71dcf8f1948b8ddfab4 ]

When the hash MMU is active the AMR, IAMR and UAMOR are used for
pkeys. The AMR is directly writable by user space, and the UAMOR masks
those writes, meaning both registers are effectively user register
state. The IAMR is used to create an execute only key.

Also we must maintain the value of at least the AMR when running in
process context, so that any memory accesses done by the kernel on
behalf of the process are correctly controlled by the AMR.

Although we are correctly switching all registers when going into a
guest, on returning to the host we just write 0 into all regs, except
on Power9 where we restore the IAMR correctly.

This could be observed by a user process if it writes the AMR, then
runs a guest and we then return immediately to it without
rescheduling. Because we have written 0 to the AMR that would have the
effect of granting read/write permission to pages that the process was
trying to protect.

In addition, when using the Radix MMU, the AMR can prevent inadvertent
kernel access to userspace data, writing 0 to the AMR disables that

So save and restore AMR, IAMR and UAMOR.

Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
Cc: # v4.16+
Signed-off-by: Russell Currey <>
Signed-off-by: Michael Ellerman <>
Acked-by: Paul Mackerras <>
Signed-off-by: Sasha Levin <>
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 26 ++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 1d14046124a01..5902a60f92268 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -56,6 +56,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
#define STACK_SLOT_DAWR (SFS-56)
+#define STACK_SLOT_AMR (SFS-80)
+#define STACK_SLOT_UAMOR (SFS-88)

* Call kvmppc_hv_entry in real mode.
@@ -760,11 +762,9 @@ BEGIN_FTR_SECTION
mfspr r5, SPRN_TIDR
mfspr r6, SPRN_PSSCR
mfspr r7, SPRN_PID
- mfspr r8, SPRN_IAMR
std r5, STACK_SLOT_TID(r1)
std r6, STACK_SLOT_PSSCR(r1)
std r7, STACK_SLOT_PID(r1)
- std r8, STACK_SLOT_IAMR(r1)
mfspr r5, SPRN_HFSCR
std r5, STACK_SLOT_HFSCR(r1)
@@ -772,11 +772,18 @@ BEGIN_FTR_SECTION
mfspr r5, SPRN_CIABR
mfspr r6, SPRN_DAWR
mfspr r7, SPRN_DAWRX
+ mfspr r8, SPRN_IAMR
std r5, STACK_SLOT_CIABR(r1)
std r6, STACK_SLOT_DAWR(r1)
std r7, STACK_SLOT_DAWRX(r1)
+ std r8, STACK_SLOT_IAMR(r1)

+ mfspr r5, SPRN_AMR
+ std r5, STACK_SLOT_AMR(r1)
+ mfspr r6, SPRN_UAMOR
+ std r6, STACK_SLOT_UAMOR(r1)
/* Set partition DABR */
/* Do this before re-enabling PMU to avoid P7 DABR corruption bug */
@@ -1713,22 +1720,25 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
mtspr SPRN_PSPB, r0
mtspr SPRN_WORT, r0
- mtspr SPRN_IAMR, r0
mtspr SPRN_TCSCR, r0
/* Set MMCRS to 1<<31 to freeze and disable the SPMC counters */
li r0, 1
sldi r0, r0, 31
mtspr SPRN_MMCRS, r0

- /* Save and reset AMR and UAMOR before turning on the MMU */
+ /* Save and restore AMR, IAMR and UAMOR before turning on the MMU */
+ ld r8, STACK_SLOT_IAMR(r1)
+ mtspr SPRN_IAMR, r8
+8: /* Power7 jumps back in here */
mfspr r5,SPRN_AMR
mfspr r6,SPRN_UAMOR
std r5,VCPU_AMR(r9)
std r6,VCPU_UAMOR(r9)
- li r6,0
- mtspr SPRN_AMR,r6
+ ld r5,STACK_SLOT_AMR(r1)
+ ld r6,STACK_SLOT_UAMOR(r1)
+ mtspr SPRN_AMR, r5
mtspr SPRN_UAMOR, r6

/* Switch DSCR back to host value */
@@ -1897,11 +1907,9 @@ BEGIN_FTR_SECTION
ld r5, STACK_SLOT_TID(r1)
ld r7, STACK_SLOT_PID(r1)
- ld r8, STACK_SLOT_IAMR(r1)
mtspr SPRN_TIDR, r5
mtspr SPRN_PSSCR, r6
mtspr SPRN_PID, r7
- mtspr SPRN_IAMR, r8


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