Subject: xen/arm: Don't expose implementation defined registers (Cp15 c15) to the guest
From: Julien Grall <[email-masked]>
Date: Tue, 15 Apr 2014 12:45:28 +0100

On Cortex-A15, CP15 c15 contains registers to retrieve data from L1/L2 RAM.

Exposing this registers to guest may result to leak data from Xen and/or
another guest.

By default trap every registers and inject an undefined instruction.

Signed-off-by: Julien Grall <[email-masked]>
Acked-by: Ian Campbell <[email-masked]>
---
 xen/arch/arm/traps.c            |    3 +++
 xen/include/asm-arm/cpregs.h    |    2 ++
 xen/include/asm-arm/processor.h |    3 +++
 3 files changed, 8 insertions(+)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index b77e623..710e5cc 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -74,6 +74,9 @@ void __cpuinit init_traps(void)
     /* Setup Hyp vector base */
     WRITE_SYSREG((vaddr_t)hyp_traps_vector, VBAR_EL2);
 
+    /* Trap CP15 c15 used for implementation defined registers */
+    WRITE_SYSREG(HSTR_T(15), HSTR_EL2);
+
     /* Trap all coprocessor registers (0-13) except cp10 and cp11 for VFP
      * /!\ All processors except cp10 and cp11 cannot be used in Xen
      */
diff --git a/xen/include/asm-arm/cpregs.h b/xen/include/asm-arm/cpregs.h
index 2b411af..e9a8094 100644
--- a/xen/include/asm-arm/cpregs.h
+++ b/xen/include/asm-arm/cpregs.h
@@ -116,6 +116,7 @@
 #define HSCTLR          p15,4,c1,c0,0   /* Hyp. System Control Register */
 #define HCR             p15,4,c1,c1,0   /* Hyp. Configuration Register */
 #define HCPTR           p15,4,c1,c1,2   /* Hyp. Coprocessor Trap Register */
+#define HSTR            p15,4,c1,c1,3   /* Hyp. System Trap Register */
 
 /* CP15 CR2: Translation Table Base and Control Registers */
 #define TTBCR           p15,0,c2,c0,2   /* Translatation Table Base Control Register */
@@ -270,6 +271,7 @@
 #define FAR_EL2                 HIFAR
 #define HCR_EL2                 HCR
 #define HPFAR_EL2               HPFAR
+#define HSTR_EL2                HSTR
 #define ID_AFR0_EL1             ID_AFR0
 #define ID_DFR0_EL1             ID_DFR0
 #define ID_ISAR0_EL1            ID_ISAR0
diff --git a/xen/include/asm-arm/processor.h b/xen/include/asm-arm/processor.h
index 02cefe9..750864a 100644
--- a/xen/include/asm-arm/processor.h
+++ b/xen/include/asm-arm/processor.h
@@ -89,6 +89,9 @@
 #define HCPTR_CP(x)     ((_AC(1,U)<<(x)))       /* Trap Coprocessor x */
 #define HCPTR_CP_MASK   ((_AC(1,U)<<14)-1)
 
+/* HSTR Hyp. System Trap Register */
+#define HSTR_T(x)       ((_AC(1,U)<<(x)))       /* Trap Cp15 c<x> */
+
 #define HSR_EC_UNKNOWN              0x00
 #define HSR_EC_WFI_WFE              0x01
 #define HSR_EC_CP15_32              0x03
-- 
1.7.10.4