[Xen-devel] [PATCH 5/9] xen: arm: Handle CP15 register traps from userspace

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Previously userspace access to PM* would have been incorrectly (but benignly)
implemented as RAZ/WI when running on a 32-bit kernel and would cause a
hypervisor exception (host crash) when running a 64-bit kernel (this was
already solved via the fix to XSA-102).

CLIDR, CCSIDR, DCCISW, ACTLR, PMINTENSET, PMINTENCLR are EL1 only, attempts to
access from EL0 will trap to EL1 not to us, hence BUG_ON is appropriate now.

PMUSERENR is R/O at EL0 and we implement as RAZ/WI at EL1 as before.

The remaining PM* registers are accessible to EL0 only if PMUSERENR_EL0.EN is
set, since we emulate this as RAZ/WI the bit is never set so we inject a trap
on attempted access. We weren't previously handling PMCCNTR.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/traps.c |   32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 46ed21d..e7a2791 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1446,6 +1446,7 @@ static void do_cp15_32(struct cpu_user_regs *regs,
     switch ( hsr.bits & HSR_CP32_REGS_MASK )
     {
     case HSR_CPREG32(CLIDR):
+        BUG_ON(psr_mode_is_user(regs));
         if ( !cp32.read )
         {
             dprintk(XENLOG_ERR,
@@ -1455,6 +1456,7 @@ static void do_cp15_32(struct cpu_user_regs *regs,
         *r = READ_SYSREG32(CLIDR_EL1);
         break;
     case HSR_CPREG32(CCSIDR):
+        BUG_ON(psr_mode_is_user(regs));
         if ( !cp32.read )
         {
             dprintk(XENLOG_ERR,
@@ -1464,6 +1466,7 @@ static void do_cp15_32(struct cpu_user_regs *regs,
         *r = READ_SYSREG32(CCSIDR_EL1);
         break;
     case HSR_CPREG32(DCCISW):
+        BUG_ON(psr_mode_is_user(regs));
         if ( cp32.read )
         {
             dprintk(XENLOG_ERR,
@@ -1481,6 +1484,7 @@ static void do_cp15_32(struct cpu_user_regs *regs,
         goto undef_cp15_32;
 
     case HSR_CPREG32(ACTLR):
+        BUG_ON(psr_mode_is_user(regs));
         if ( cp32.read )
            *r = v->arch.actlr;
         break;
@@ -1493,6 +1497,18 @@ static void do_cp15_32(struct cpu_user_regs *regs,
      * always support PMCCNTR (the cyle counter): we just RAZ/WI for all
      * PM register, which doesn't crash the kernel at least
      */
+    case HSR_CPREG32(PMUSERENR):
+        /* RO at EL0. RAZ/WI at EL1 */
+        if ( psr_mode_is_user(regs) && !hsr.cp32.read )
+            goto undef_cp15_32;
+        goto cp15_32_raz_wi;
+
+    case HSR_CPREG32(PMINTENSET):
+    case HSR_CPREG32(PMINTENCLR):
+        /* EL1 only */
+        BUG_ON(psr_mode_is_user(regs));
+        goto cp15_32_raz_wi;
+
     case HSR_CPREG32(PMCR):
     case HSR_CPREG32(PMCNTENSET):
     case HSR_CPREG32(PMCNTENCLR):
@@ -1504,12 +1520,19 @@ static void do_cp15_32(struct cpu_user_regs *regs,
     case HSR_CPREG32(PMCCNTR):
     case HSR_CPREG32(PMXEVTYPER):
     case HSR_CPREG32(PMXEVCNTR):
-    case HSR_CPREG32(PMUSERENR):
-    case HSR_CPREG32(PMINTENSET):
-    case HSR_CPREG32(PMINTENCLR):
     case HSR_CPREG32(PMOVSSET):
+        /*
+         * Accessible at EL0 only if PMUSERENR_EL0.EN is set. We
+         * emulate that register as 0 above.
+         */
+        if ( psr_mode_is_user(regs) )
+            goto undef_cp15_32;
+        /* Fall thru */
+
+ cp15_32_raz_wi:
         if ( cp32.read )
             *r = 0;
+        /* else: write ignored */
         break;
 
     default:
@@ -1908,8 +1931,7 @@ asmlinkage void do_trap_hypervisor(struct cpu_user_regs 
*regs)
         advance_pc(regs, hsr);
         break;
     case HSR_EC_CP15_32:
-        if ( !is_32bit_domain(current->domain) )
-            goto bad_trap;
+        BUG_ON(!psr_mode_is_32bit(regs->cpsr));
         do_cp15_32(regs, hsr);
         break;
     case HSR_EC_CP15_64:
-- 
1.7.10.4


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