From 0aa27ce3351f7eb09d13e863a1d5f303086aa32a Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Fri, 4 Oct 2013 12:23:23 +0200 Subject: x86/idle: Fix get_cpu_idle_time()'s interaction with offline pcpus Checking for "idle_vcpu[cpu] != NULL" is insufficient protection against offline pcpus. From a hypercall, vcpu_runstate_get() will determine "v != current", and try to take the vcpu_schedule_lock(). This will try to look up per_cpu(schedule_data, v->processor) and promptly suffer a NULL structure deference as v->processors' __per_cpu_offset is INVALID_PERCPU_AREA. One example might look like this: ... Xen call trace: [] vcpu_runstate_get+0x50/0x113 [] get_cpu_idle_time+0x28/0x2e [] do_sysctl+0x3db/0xeb8 [] compat_hypercall+0xbd/0x116 Pagetable walk from 0000000000000040: L4[0x000] = 0000000186df8027 0000000000028207 L3[0x000] = 0000000188e36027 00000000000261c9 L2[0x000] = 0000000000000000 ffffffffffffffff **************************************** Panic on CPU 11: ... get_cpu_idle_time() has been updated to correctly deal with offline pcpus itself by returning 0, in the same way as it would if it was missing the idle_vcpu[] pointer. In doing so, XENPF_getidletime needed updating to correctly retain its described behaviour of clearing bits in the cpumap for offline pcpus. As this crash can only be triggered with toolstack hypercalls, it is not a security issue and just a simple bug. Signed-off-by: Andrew Cooper Acked-by: Keir Fraser --- xen/arch/x86/platform_hypercall.c | 8 ++++++-- xen/common/schedule.c | 9 ++++----- 2 files changed, 10 insertions(+), 7 deletions(-) diff --git a/xen/arch/x86/platform_hypercall.c b/xen/arch/x86/platform_hypercall.c index 7175a82658..2162811300 100644 --- a/xen/arch/x86/platform_hypercall.c +++ b/xen/arch/x86/platform_hypercall.c @@ -355,10 +355,14 @@ ret_t do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op) for_each_cpu ( cpu, cpumap ) { - if ( idle_vcpu[cpu] == NULL ) - cpumask_clear_cpu(cpu, cpumap); idletime = get_cpu_idle_time(cpu); + if ( !idletime ) + { + cpumask_clear_cpu(cpu, cpumap); + continue; + } + if ( copy_to_guest_offset(idletimes, cpu, &idletime, 1) ) { ret = -EFAULT; diff --git a/xen/common/schedule.c b/xen/common/schedule.c index a8398bd9ed..1ddfb22df6 100644 --- a/xen/common/schedule.c +++ b/xen/common/schedule.c @@ -176,13 +176,12 @@ void vcpu_runstate_get(struct vcpu *v, struct vcpu_runstate_info *runstate) uint64_t get_cpu_idle_time(unsigned int cpu) { - struct vcpu_runstate_info state; - struct vcpu *v; + struct vcpu_runstate_info state = { 0 }; + struct vcpu *v = idle_vcpu[cpu]; - if ( (v = idle_vcpu[cpu]) == NULL ) - return 0; + if ( cpu_online(cpu) && v ) + vcpu_runstate_get(v, &state); - vcpu_runstate_get(v, &state); return state.time[RUNSTATE_running]; } -- cgit v1.2.3