From c8e2fe13d1d1f3a02842b7b909d4e4846a4b6a2c Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 9 Mar 2021 09:10:19 -0800 Subject: [PATCH] x86/perf: Use RET0 as default for guest_get_msrs to handle "no PMU" case Initialize x86_pmu.guest_get_msrs to return 0/NULL to handle the "nop" case. Patching in perf_guest_get_msrs_nop() during setup does not work if there is no PMU, as setup bails before updating the static calls, leaving x86_pmu.guest_get_msrs NULL and thus a complete nop. Ultimately, this causes VMX abort on VM-Exit due to KVM putting random garbage from the stack into the MSR load list. Add a comment in KVM to note that nr_msrs is valid if and only if the return value is non-NULL. Fixes: abd562df94d1 ("x86/perf: Use static_call for x86_pmu.guest_get_msrs") Reported-by: Dmitry Vyukov Reported-by: syzbot+cce9ef2dd25246f815ee@syzkaller.appspotmail.com Suggested-by: Peter Zijlstra Signed-off-by: Sean Christopherson Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210309171019.1125243-1-seanjc@google.com --- arch/x86/events/core.c | 15 ++++++--------- arch/x86/kvm/vmx/vmx.c | 2 +- 2 files changed, 7 insertions(+), 10 deletions(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 6ddeed3cd2ac..18df17129695 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -81,7 +81,11 @@ DEFINE_STATIC_CALL_NULL(x86_pmu_swap_task_ctx, *x86_pmu.swap_task_ctx); DEFINE_STATIC_CALL_NULL(x86_pmu_drain_pebs, *x86_pmu.drain_pebs); DEFINE_STATIC_CALL_NULL(x86_pmu_pebs_aliases, *x86_pmu.pebs_aliases); -DEFINE_STATIC_CALL_NULL(x86_pmu_guest_get_msrs, *x86_pmu.guest_get_msrs); +/* + * This one is magic, it will get called even when PMU init fails (because + * there is no PMU), in which case it should simply return NULL. + */ +DEFINE_STATIC_CALL_RET0(x86_pmu_guest_get_msrs, *x86_pmu.guest_get_msrs); u64 __read_mostly hw_cache_event_ids [PERF_COUNT_HW_CACHE_MAX] @@ -1944,13 +1948,6 @@ static void _x86_pmu_read(struct perf_event *event) x86_perf_event_update(event); } -static inline struct perf_guest_switch_msr * -perf_guest_get_msrs_nop(int *nr) -{ - *nr = 0; - return NULL; -} - static int __init init_hw_perf_events(void) { struct x86_pmu_quirk *quirk; @@ -2025,7 +2022,7 @@ static int __init init_hw_perf_events(void) x86_pmu.read = _x86_pmu_read; if (!x86_pmu.guest_get_msrs) - x86_pmu.guest_get_msrs = perf_guest_get_msrs_nop; + x86_pmu.guest_get_msrs = (void *)&__static_call_return0; x86_pmu_static_call_update(); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 50810d471462..32cf8287d4a7 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6580,8 +6580,8 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx) int i, nr_msrs; struct perf_guest_switch_msr *msrs; + /* Note, nr_msrs may be garbage if perf_guest_get_msrs() returns NULL. */ msrs = perf_guest_get_msrs(&nr_msrs); - if (!msrs) return;