xen: arm: Correctly handle do_sysreg exception injection from 64-bit userspace

The do_sysreg case was missing a return, so it would increment PC and
inject the trap to the second instruction of the handler.

This is CVE-2014-5148 / XSA-103.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index ae594caea72d0bda315d0043cb612d16ac0698a2..683b4400f9d43de970cff93121088de7e507c4bc 100644 (file)
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1704,6 +1704,7 @@ static void do_sysreg(struct cpu_user_regs *regs,
                      hsr.bits & HSR_SYSREG_REGS_MASK);
 #endif
             inject_undef_exception(regs, sysreg.len);
+            return;
         }
     }