From 22c096c99d8c05833c3c19870e36efb2dd4e8013 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 2 May 2017 14:45:02 +0200 Subject: [PATCH] multicall: deal with early exit conditions In particular changes to guest privilege level require the multicall sequence to be aborted, as hypercalls are permitted from kernel mode only. While likely not very useful in a multicall, also properly handle the return value in the HYPERVISOR_iret case (which should be the guest specified value). This is XSA-213. Reported-by: Jann Horn Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper Acked-by: Julien Grall --- xen/arch/arm/traps.c | 11 +++++++---- xen/arch/x86/pv/hypercall.c | 26 ++++++++++++++++++-------- xen/common/multicall.c | 17 ++++++++++++++--- xen/include/xen/multicall.h | 6 +++++- 4 files changed, 44 insertions(+), 16 deletions(-) diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c index 6bed039ced..6010c96c54 100644 --- a/xen/arch/arm/traps.c +++ b/xen/arch/arm/traps.c @@ -1653,7 +1653,7 @@ static bool check_multicall_32bit_clean(struct multicall_entry *multi) return true; } -void arch_do_multicall_call(struct mc_state *state) +enum mc_disposition arch_do_multicall_call(struct mc_state *state) { struct multicall_entry *multi = &state->call; arm_hypercall_fn_t call = NULL; @@ -1661,23 +1661,26 @@ void arch_do_multicall_call(struct mc_state *state) if ( multi->op >= ARRAY_SIZE(arm_hypercall_table) ) { multi->result = -ENOSYS; - return; + return mc_continue; } call = arm_hypercall_table[multi->op].fn; if ( call == NULL ) { multi->result = -ENOSYS; - return; + return mc_continue; } if ( is_32bit_domain(current->domain) && !check_multicall_32bit_clean(multi) ) - return; + return mc_continue; multi->result = call(multi->args[0], multi->args[1], multi->args[2], multi->args[3], multi->args[4]); + + return likely(!psr_mode_is_user(guest_cpu_user_regs())) + ? mc_continue : mc_preempt; } /* diff --git a/xen/arch/x86/pv/hypercall.c b/xen/arch/x86/pv/hypercall.c index 9d29d2f088..7c5e5a629d 100644 --- a/xen/arch/x86/pv/hypercall.c +++ b/xen/arch/x86/pv/hypercall.c @@ -215,15 +215,19 @@ void pv_hypercall(struct cpu_user_regs *regs) perfc_incr(hypercalls); } -void arch_do_multicall_call(struct mc_state *state) +enum mc_disposition arch_do_multicall_call(struct mc_state *state) { - if ( !is_pv_32bit_vcpu(current) ) + struct vcpu *curr = current; + unsigned long op; + + if ( !is_pv_32bit_vcpu(curr) ) { struct multicall_entry *call = &state->call; - if ( (call->op < ARRAY_SIZE(pv_hypercall_table)) && - pv_hypercall_table[call->op].native ) - call->result = pv_hypercall_table[call->op].native( + op = call->op; + if ( (op < ARRAY_SIZE(pv_hypercall_table)) && + pv_hypercall_table[op].native ) + call->result = pv_hypercall_table[op].native( call->args[0], call->args[1], call->args[2], call->args[3], call->args[4], call->args[5]); else @@ -234,15 +238,21 @@ void arch_do_multicall_call(struct mc_state *state) { struct compat_multicall_entry *call = &state->compat_call; - if ( (call->op < ARRAY_SIZE(pv_hypercall_table)) && - pv_hypercall_table[call->op].compat ) - call->result = pv_hypercall_table[call->op].compat( + op = call->op; + if ( (op < ARRAY_SIZE(pv_hypercall_table)) && + pv_hypercall_table[op].compat ) + call->result = pv_hypercall_table[op].compat( call->args[0], call->args[1], call->args[2], call->args[3], call->args[4], call->args[5]); else call->result = -ENOSYS; } #endif + + return unlikely(op == __HYPERVISOR_iret) + ? mc_exit + : likely(guest_kernel_mode(curr, guest_cpu_user_regs())) + ? mc_continue : mc_preempt; } /* diff --git a/xen/common/multicall.c b/xen/common/multicall.c index cc8daf919f..7cbf857048 100644 --- a/xen/common/multicall.c +++ b/xen/common/multicall.c @@ -39,6 +39,7 @@ do_multicall( struct mc_state *mcs = ¤t->mc_state; uint32_t i; int rc = 0; + enum mc_disposition disp = mc_continue; if ( unlikely(__test_and_set_bit(_MCSF_in_multicall, &mcs->flags)) ) { @@ -49,7 +50,7 @@ do_multicall( if ( unlikely(!guest_handle_okay(call_list, nr_calls)) ) rc = -EFAULT; - for ( i = 0; !rc && i < nr_calls; i++ ) + for ( i = 0; !rc && disp == mc_continue && i < nr_calls; i++ ) { if ( i && hypercall_preempt_check() ) goto preempted; @@ -62,7 +63,7 @@ do_multicall( trace_multicall_call(&mcs->call); - arch_do_multicall_call(mcs); + disp = arch_do_multicall_call(mcs); #ifndef NDEBUG { @@ -76,7 +77,14 @@ do_multicall( } #endif - if ( unlikely(__copy_field_to_guest(call_list, &mcs->call, result)) ) + if ( unlikely(disp == mc_exit) ) + { + if ( __copy_field_to_guest(call_list, &mcs->call, result) ) + /* nothing, best effort only */; + rc = mcs->call.result; + } + else if ( unlikely(__copy_field_to_guest(call_list, &mcs->call, + result)) ) rc = -EFAULT; else if ( current->hcall_preempted ) { @@ -94,6 +102,9 @@ do_multicall( guest_handle_add_offset(call_list, 1); } + if ( unlikely(disp == mc_preempt) && i < nr_calls ) + goto preempted; + perfc_incr(calls_to_multicall); perfc_add(calls_from_multicall, i); mcs->flags = 0; diff --git a/xen/include/xen/multicall.h b/xen/include/xen/multicall.h index e8d7905a0f..d0aa52009c 100644 --- a/xen/include/xen/multicall.h +++ b/xen/include/xen/multicall.h @@ -22,6 +22,10 @@ struct mc_state { }; }; -void arch_do_multicall_call(struct mc_state *mc); +enum mc_disposition { + mc_continue, + mc_exit, + mc_preempt, +} arch_do_multicall_call(struct mc_state *mc); #endif /* __XEN_MULTICALL_H__ */ -- 2.30.2