Alexandru Matei <alexandru.matei@xxxxxxxxxx> writes: > KVM enables 'Enlightened VMCS' and 'Enlightened MSR Bitmap' when running as > a nested hypervisor on top of Hyper-V. When MSR bitmap is updated, > evmcs_touch_msr_bitmap function uses current_vmcs per-cpu variable to mark > that the msr bitmap was changed. > > vmx_vcpu_create() modifies the msr bitmap via vmx_disable_intercept_for_msr > -> vmx_msr_bitmap_l01_changed which in the end calls this function. The > function checks for current_vmcs if it is null but the check is > insufficient because current_vmcs is not initialized. Because of this, the > code might incorrectly write to the structure pointed by current_vmcs value > left by another task. Preemption is not disabled, the current task can be > preempted and moved to another CPU while current_vmcs is accessed multiple > times from evmcs_touch_msr_bitmap() which leads to crash. > > The manipulation of MSR bitmaps by callers happens only for vmcs01 so the > solution is to use vmx->vmcs01.vmcs instead of current_vmcs. > > BUG: kernel NULL pointer dereference, address: 0000000000000338 > PGD 4e1775067 P4D 0 > Oops: 0002 [#1] PREEMPT SMP NOPTI > ... > RIP: 0010:vmx_msr_bitmap_l01_changed+0x39/0x50 [kvm_intel] > ... > Call Trace: > vmx_disable_intercept_for_msr+0x36/0x260 [kvm_intel] > vmx_vcpu_create+0xe6/0x540 [kvm_intel] > ? __vmalloc_node+0x4a/0x70 > kvm_arch_vcpu_create+0x1d1/0x2e0 [kvm] > kvm_vm_ioctl_create_vcpu+0x178/0x430 [kvm] > ? __handle_mm_fault+0x3cb/0x750 > kvm_vm_ioctl+0x53f/0x790 [kvm] > ? syscall_exit_work+0x11a/0x150 > ? syscall_exit_to_user_mode+0x12/0x30 > ? do_syscall_64+0x69/0x90 > ? handle_mm_fault+0xc5/0x2a0 > __x64_sys_ioctl+0x8a/0xc0 > do_syscall_64+0x5c/0x90 > ? exc_page_fault+0x62/0x150 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Alexandru Matei <alexandru.matei@xxxxxxxxxx> > --- > v2: > - pass (e)vmcs01 to evmcs_touch_msr_bitmap > - use loaded_vmcs * instead of vcpu_vmx * to avoid > including vmx.h which generates circular dependency > > v1: https://lore.kernel.org/kvm/20230118141348.828-1-alexandru.matei@xxxxxxxxxx/ > > arch/x86/kvm/vmx/hyperv.h | 16 +++++++++++----- > arch/x86/kvm/vmx/vmx.c | 2 +- > 2 files changed, 12 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/vmx/hyperv.h b/arch/x86/kvm/vmx/hyperv.h > index 571e7929d14e..132e32e57d2d 100644 > --- a/arch/x86/kvm/vmx/hyperv.h > +++ b/arch/x86/kvm/vmx/hyperv.h > @@ -190,13 +190,19 @@ static inline u16 evmcs_read16(unsigned long field) > return *(u16 *)((char *)current_evmcs + offset); > } > > -static inline void evmcs_touch_msr_bitmap(void) > +static inline void evmcs_touch_msr_bitmap(struct loaded_vmcs *vmcs01) Personally, I would've followed Sean's suggestion and passed "struct vcpu_vmx *vmx" as 'loaded_vmcs' here is a bit ambiguos.... > { > - if (unlikely(!current_evmcs)) > + /* > + * Enlightened MSR Bitmap feature is enabled only for L1, i.e. > + * always operates on (e)vmcs01 > + */ > + struct hv_enlightened_vmcs* evmcs = (void*)vmcs01->vmcs; (Nit: a space between "void" and "*") .. or, alternatively, you can directly pass (struct hv_enlightened_vmcs *)vmx->vmcs01.vmcs as e.g. 'current_evmcs' and avoid the conversion here. > + > + if (WARN_ON_ONCE(!evmcs)) > return; > > - if (current_evmcs->hv_enlightenments_control.msr_bitmap) > - current_evmcs->hv_clean_fields &= > + if (evmcs->hv_enlightenments_control.msr_bitmap) > + evmcs->hv_clean_fields &= > ~HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP; > } > > @@ -219,7 +225,7 @@ static inline u64 evmcs_read64(unsigned long field) { return 0; } > static inline u32 evmcs_read32(unsigned long field) { return 0; } > static inline u16 evmcs_read16(unsigned long field) { return 0; } > static inline void evmcs_load(u64 phys_addr) {} > -static inline void evmcs_touch_msr_bitmap(void) {} > +static inline void evmcs_touch_msr_bitmap(struct loaded_vmcs *vmcs01) {} > #endif /* IS_ENABLED(CONFIG_HYPERV) */ > > #define EVMPTR_INVALID (-1ULL) > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index fe5615fd8295..2a3be8e8a1bf 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -3869,7 +3869,7 @@ static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx) > * bitmap has changed. > */ > if (static_branch_unlikely(&enable_evmcs)) > - evmcs_touch_msr_bitmap(); > + evmcs_touch_msr_bitmap(&vmx->vmcs01); > > vmx->nested.force_msr_bitmap_recalc = true; > } -- Vitaly
