Message ID | 20210504171734.1434054-9-seanjc@google.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups | expand |
On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote: > Configure the list of user return MSRs that are actually supported at > module init instead of reprobing the list of possible MSRs every time a > vCPU is created. Curating the list on a per-vCPU basis is pointless; KVM > is completely hosed if the set of supported MSRs changes after module init, > or if the set of MSRs differs per physical PCU. > > The per-vCPU lists also increase complexity (see __vmx_find_uret_msr()) and > creates corner cases that _should_ be impossible, but theoretically exist > in KVM, e.g. advertising RDTSCP to userspace without actually being able to > virtualize RDTSCP if probing MSR_TSC_AUX fails. > > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/vmx/vmx.c | 61 ++++++++++++++++++++++++++++-------------- > arch/x86/kvm/vmx/vmx.h | 10 ++++++- > 2 files changed, 50 insertions(+), 21 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 42e4bbaa299a..68454b0de2b1 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -461,7 +461,7 @@ static unsigned long host_idt_base; > * support this emulation, IA32_STAR must always be included in > * vmx_uret_msrs_list[], even in i386 builds. > */ > -static const u32 vmx_uret_msrs_list[] = { > +static u32 vmx_uret_msrs_list[] = { > #ifdef CONFIG_X86_64 > MSR_SYSCALL_MASK, MSR_LSTAR, MSR_CSTAR, > #endif > @@ -469,6 +469,12 @@ static const u32 vmx_uret_msrs_list[] = { > MSR_IA32_TSX_CTRL, > }; > > +/* > + * Number of user return MSRs that are actually supported in hardware. > + * vmx_uret_msrs_list is modified when KVM is loaded to drop unsupported MSRs. > + */ > +static int vmx_nr_uret_msrs; > + > #if IS_ENABLED(CONFIG_HYPERV) > static bool __read_mostly enlightened_vmcs = true; > module_param(enlightened_vmcs, bool, 0444); > @@ -700,9 +706,16 @@ static inline int __vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr) > { > int i; > > - for (i = 0; i < vmx->nr_uret_msrs; ++i) > + /* > + * Note, vmx->guest_uret_msrs is the same size as vmx_uret_msrs_list, > + * but is ordered differently. The MSR is matched against the list of > + * supported uret MSRs using "slot", but the index that is returned is > + * the index into guest_uret_msrs. > + */ > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > if (vmx_uret_msrs_list[vmx->guest_uret_msrs[i].slot] == msr) > return i; > + } > return -1; > } > > @@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) > goto free_vpid; > } > > - BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > + vmx->guest_uret_msrs[i].data = 0; > > - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { > - u32 index = vmx_uret_msrs_list[i]; > - int j = vmx->nr_uret_msrs; > - > - if (kvm_probe_user_return_msr(index)) > - continue; > - > - vmx->guest_uret_msrs[j].slot = i; I don't see anything initalizing the .slot after this patch. Now this code is removed later which masks this bug, but for the bisect sake, I think that this patch should still be fixed. Other than this minor bug: Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Best regards, Maxim Levitsky > - vmx->guest_uret_msrs[j].data = 0; > - switch (index) { > + switch (vmx_uret_msrs_list[i]) { > case MSR_IA32_TSX_CTRL: > /* > * TSX_CTRL_CPUID_CLEAR is handled in the CPUID > @@ -6954,15 +6959,14 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) > * host so that TSX remains always disabled. > */ > if (boot_cpu_has(X86_FEATURE_RTM)) > - vmx->guest_uret_msrs[j].mask = ~(u64)TSX_CTRL_CPUID_CLEAR; > + vmx->guest_uret_msrs[i].mask = ~(u64)TSX_CTRL_CPUID_CLEAR; > else > - vmx->guest_uret_msrs[j].mask = 0; > + vmx->guest_uret_msrs[i].mask = 0; > break; > default: > - vmx->guest_uret_msrs[j].mask = -1ull; > + vmx->guest_uret_msrs[i].mask = -1ull; > break; > } > - ++vmx->nr_uret_msrs; > } > > err = alloc_loaded_vmcs(&vmx->vmcs01); > @@ -7821,17 +7825,34 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = { > .vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector, > }; > > +static __init void vmx_setup_user_return_msrs(void) > +{ > + u32 msr; > + int i; > + > + BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); > + > + for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { > + msr = vmx_uret_msrs_list[i]; > + > + if (kvm_probe_user_return_msr(msr)) > + continue; > + > + kvm_define_user_return_msr(vmx_nr_uret_msrs, msr); > + vmx_uret_msrs_list[vmx_nr_uret_msrs++] = msr; > + } > +} > + > static __init int hardware_setup(void) > { > unsigned long host_bndcfgs; > struct desc_ptr dt; > - int r, i, ept_lpage_level; > + int r, ept_lpage_level; > > store_idt(&dt); > host_idt_base = dt.address; > > - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) > - kvm_define_user_return_msr(i, vmx_uret_msrs_list[i]); > + vmx_setup_user_return_msrs(); > > if (setup_vmcs_config(&vmcs_config, &vmx_capability) < 0) > return -EIO; > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index 008cb87ff088..d71ed8b425c5 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -245,8 +245,16 @@ struct vcpu_vmx { > u32 idt_vectoring_info; > ulong rflags; > > + /* > + * User return MSRs are always emulated when enabled in the guest, but > + * only loaded into hardware when necessary, e.g. SYSCALL #UDs outside > + * of 64-bit mode or if EFER.SCE=1, thus the SYSCALL MSRs don't need to > + * be loaded into hardware if those conditions aren't met. > + * nr_active_uret_msrs tracks the number of MSRs that need to be loaded > + * into hardware when running the guest. guest_uret_msrs[] is resorted > + * whenever the number of "active" uret MSRs is modified. > + */ > struct vmx_uret_msr guest_uret_msrs[MAX_NR_USER_RETURN_MSRS]; > - int nr_uret_msrs; > int nr_active_uret_msrs; > bool guest_uret_msrs_loaded; > #ifdef CONFIG_X86_64
On Mon, May 10, 2021, Maxim Levitsky wrote: > On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote: > > @@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) > > goto free_vpid; > > } > > > > - BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); > > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > > + vmx->guest_uret_msrs[i].data = 0; > > > > - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { > > - u32 index = vmx_uret_msrs_list[i]; > > - int j = vmx->nr_uret_msrs; > > - > > - if (kvm_probe_user_return_msr(index)) > > - continue; > > - > > - vmx->guest_uret_msrs[j].slot = i; > I don't see anything initalizing the .slot after this patch. > Now this code is removed later which masks this bug, > but for the bisect sake, I think that this patch > should still be fixed. Egad, indeed it's broken. I'll retest the whole series to verify the other patches will bisect cleanly. Nice catch!
On Mon, 2021-05-10 at 15:13 +0000, Sean Christopherson wrote: > On Mon, May 10, 2021, Maxim Levitsky wrote: > > On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote: > > > @@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) > > > goto free_vpid; > > > } > > > > > > - BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); > > > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > > > + vmx->guest_uret_msrs[i].data = 0; > > > > > > - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { > > > - u32 index = vmx_uret_msrs_list[i]; > > > - int j = vmx->nr_uret_msrs; > > > - > > > - if (kvm_probe_user_return_msr(index)) > > > - continue; > > > - > > > - vmx->guest_uret_msrs[j].slot = i; > > I don't see anything initalizing the .slot after this patch. > > Now this code is removed later which masks this bug, > > but for the bisect sake, I think that this patch > > should still be fixed. > > Egad, indeed it's broken. I'll retest the whole series to verify the other > patches will bisect cleanly. > > Nice catch! > Thanks! Best regards, Maxim Levitsky
On Tue, May 11, 2021, Maxim Levitsky wrote: > On Mon, 2021-05-10 at 15:13 +0000, Sean Christopherson wrote: > > On Mon, May 10, 2021, Maxim Levitsky wrote: > > > On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote: > > > > @@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) > > > > goto free_vpid; > > > > } > > > > > > > > - BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); > > > > + for (i = 0; i < vmx_nr_uret_msrs; ++i) { > > > > + vmx->guest_uret_msrs[i].data = 0; > > > > > > > > - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { > > > > - u32 index = vmx_uret_msrs_list[i]; > > > > - int j = vmx->nr_uret_msrs; > > > > - > > > > - if (kvm_probe_user_return_msr(index)) > > > > - continue; > > > > - > > > > - vmx->guest_uret_msrs[j].slot = i; > > > I don't see anything initalizing the .slot after this patch. > > > Now this code is removed later which masks this bug, > > > but for the bisect sake, I think that this patch > > > should still be fixed. > > > > Egad, indeed it's broken. I'll retest the whole series to verify the other > > patches will bisect cleanly. > > > > Nice catch! > > > Thanks! Unfortunately this made it's way to Linus before I could fix my goof. Fingers crossed no one is unfortunate enough to land on this while bisecting...
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 42e4bbaa299a..68454b0de2b1 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -461,7 +461,7 @@ static unsigned long host_idt_base; * support this emulation, IA32_STAR must always be included in * vmx_uret_msrs_list[], even in i386 builds. */ -static const u32 vmx_uret_msrs_list[] = { +static u32 vmx_uret_msrs_list[] = { #ifdef CONFIG_X86_64 MSR_SYSCALL_MASK, MSR_LSTAR, MSR_CSTAR, #endif @@ -469,6 +469,12 @@ static const u32 vmx_uret_msrs_list[] = { MSR_IA32_TSX_CTRL, }; +/* + * Number of user return MSRs that are actually supported in hardware. + * vmx_uret_msrs_list is modified when KVM is loaded to drop unsupported MSRs. + */ +static int vmx_nr_uret_msrs; + #if IS_ENABLED(CONFIG_HYPERV) static bool __read_mostly enlightened_vmcs = true; module_param(enlightened_vmcs, bool, 0444); @@ -700,9 +706,16 @@ static inline int __vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr) { int i; - for (i = 0; i < vmx->nr_uret_msrs; ++i) + /* + * Note, vmx->guest_uret_msrs is the same size as vmx_uret_msrs_list, + * but is ordered differently. The MSR is matched against the list of + * supported uret MSRs using "slot", but the index that is returned is + * the index into guest_uret_msrs. + */ + for (i = 0; i < vmx_nr_uret_msrs; ++i) { if (vmx_uret_msrs_list[vmx->guest_uret_msrs[i].slot] == msr) return i; + } return -1; } @@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) goto free_vpid; } - BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); + for (i = 0; i < vmx_nr_uret_msrs; ++i) { + vmx->guest_uret_msrs[i].data = 0; - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { - u32 index = vmx_uret_msrs_list[i]; - int j = vmx->nr_uret_msrs; - - if (kvm_probe_user_return_msr(index)) - continue; - - vmx->guest_uret_msrs[j].slot = i; - vmx->guest_uret_msrs[j].data = 0; - switch (index) { + switch (vmx_uret_msrs_list[i]) { case MSR_IA32_TSX_CTRL: /* * TSX_CTRL_CPUID_CLEAR is handled in the CPUID @@ -6954,15 +6959,14 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) * host so that TSX remains always disabled. */ if (boot_cpu_has(X86_FEATURE_RTM)) - vmx->guest_uret_msrs[j].mask = ~(u64)TSX_CTRL_CPUID_CLEAR; + vmx->guest_uret_msrs[i].mask = ~(u64)TSX_CTRL_CPUID_CLEAR; else - vmx->guest_uret_msrs[j].mask = 0; + vmx->guest_uret_msrs[i].mask = 0; break; default: - vmx->guest_uret_msrs[j].mask = -1ull; + vmx->guest_uret_msrs[i].mask = -1ull; break; } - ++vmx->nr_uret_msrs; } err = alloc_loaded_vmcs(&vmx->vmcs01); @@ -7821,17 +7825,34 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = { .vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector, }; +static __init void vmx_setup_user_return_msrs(void) +{ + u32 msr; + int i; + + BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS); + + for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) { + msr = vmx_uret_msrs_list[i]; + + if (kvm_probe_user_return_msr(msr)) + continue; + + kvm_define_user_return_msr(vmx_nr_uret_msrs, msr); + vmx_uret_msrs_list[vmx_nr_uret_msrs++] = msr; + } +} + static __init int hardware_setup(void) { unsigned long host_bndcfgs; struct desc_ptr dt; - int r, i, ept_lpage_level; + int r, ept_lpage_level; store_idt(&dt); host_idt_base = dt.address; - for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) - kvm_define_user_return_msr(i, vmx_uret_msrs_list[i]); + vmx_setup_user_return_msrs(); if (setup_vmcs_config(&vmcs_config, &vmx_capability) < 0) return -EIO; diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 008cb87ff088..d71ed8b425c5 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -245,8 +245,16 @@ struct vcpu_vmx { u32 idt_vectoring_info; ulong rflags; + /* + * User return MSRs are always emulated when enabled in the guest, but + * only loaded into hardware when necessary, e.g. SYSCALL #UDs outside + * of 64-bit mode or if EFER.SCE=1, thus the SYSCALL MSRs don't need to + * be loaded into hardware if those conditions aren't met. + * nr_active_uret_msrs tracks the number of MSRs that need to be loaded + * into hardware when running the guest. guest_uret_msrs[] is resorted + * whenever the number of "active" uret MSRs is modified. + */ struct vmx_uret_msr guest_uret_msrs[MAX_NR_USER_RETURN_MSRS]; - int nr_uret_msrs; int nr_active_uret_msrs; bool guest_uret_msrs_loaded; #ifdef CONFIG_X86_64
Configure the list of user return MSRs that are actually supported at module init instead of reprobing the list of possible MSRs every time a vCPU is created. Curating the list on a per-vCPU basis is pointless; KVM is completely hosed if the set of supported MSRs changes after module init, or if the set of MSRs differs per physical PCU. The per-vCPU lists also increase complexity (see __vmx_find_uret_msr()) and creates corner cases that _should_ be impossible, but theoretically exist in KVM, e.g. advertising RDTSCP to userspace without actually being able to virtualize RDTSCP if probing MSR_TSC_AUX fails. Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/vmx/vmx.c | 61 ++++++++++++++++++++++++++++-------------- arch/x86/kvm/vmx/vmx.h | 10 ++++++- 2 files changed, 50 insertions(+), 21 deletions(-)