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Peter Anvin" Subject: [PATCH kernel v3 2/3] KVM: SEV: Enable data breakpoints in SEV-ES Date: Fri, 20 Jan 2023 14:10:46 +1100 Message-ID: <20230120031047.628097-3-aik@amd.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20230120031047.628097-1-aik@amd.com> References: <20230120031047.628097-1-aik@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6NAM11FT088:EE_|CH0PR12MB5346:EE_ X-MS-Office365-Filtering-Correlation-Id: cbb716e6-1cca-4e40-d1d6-08dafa94383e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230022)(4636009)(136003)(376002)(39860400002)(396003)(346002)(451199015)(46966006)(40470700004)(36840700001)(82310400005)(356005)(6200100001)(40480700001)(36860700001)(478600001)(336012)(2906002)(37006003)(316002)(82740400003)(7416002)(1076003)(5660300002)(4326008)(2616005)(81166007)(54906003)(70586007)(70206006)(40460700003)(47076005)(83380400001)(7049001)(426003)(6862004)(41300700001)(8936002)(186003)(8676002)(16526019)(26005)(36756003)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Jan 2023 03:12:53.1153 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: cbb716e6-1cca-4e40-d1d6-08dafa94383e X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT088.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR12MB5346 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Prior to SEV-ES, KVM stored/loaded host debug registers upon switching to/from a VM. Changing those registers inside a running SEV VM triggered #VC exit to KVM. SEV-ES added the encrypted state (ES) which uses an encrypted guest page for the VM state (VMSA). The hardware saves/restores certain registers on VMRUN/VMEXIT according to a swap type (A, B, C), see "Table B-3. Swap Types" in the AMD Architecture Programmer’s Manual volume 2. AMD Milan (Fam 19h) introduces support for the debug registers swapping. DR6 and DR7 are always swapped. DR[0-3] and DR[0-3]_ADDR_MASK are swapped a type B when SEV_FEATURES[5] ("DebugSwap") is set. Enable DebugSwap in VMSA. But only do so if CPUID Fn80000021_EAX[0] ("NoNestedDataBp", "Processor ignores nested data breakpoints") is supported by the SOC as otherwise a malicious SEV-ES guest can set up data breakpoints on the #VC IDT entry/stack and cause an infinite loop. Eliminate DR7 and #DB intercepts as: - they are not needed when DebugSwap is supported; - #VC for these intercepts is most likely not supported anyway and kills the VM. Keep DR7 intercepted unless DebugSwap enabled to prevent the infinite #DB loop DoS. Signed-off-by: Alexey Kardashevskiy --- Changes: v3: * rewrote the commit log again * rebased on tip/master to use recently defined X86_FEATURE_NO_NESTED_DATA_BP * s/boot_cpu_has/cpu_feature_enabled/ v2: * debug_swap moved from vcpu to module_param * rewrote commit log --- Tested with: === int x; int main(int argc, char *argv[]) { x = 1; return 0; } === gcc -g a.c rsync a.out ruby-954vm:~/ ssh -t ruby-954vm 'gdb -ex "file a.out" -ex "watch x" -ex r' where ruby-954vm is a VM. With "/sys/module/kvm_amd/parameters/debug_swap = 0", gdb does not stop on the watchpoint, with "= 1" - gdb does. --- arch/x86/include/asm/svm.h | 1 + arch/x86/kvm/svm/svm.h | 16 ++++++++--- arch/x86/kvm/svm/sev.c | 29 ++++++++++++++++++++ arch/x86/kvm/svm/svm.c | 3 +- 4 files changed, 44 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h index cb1ee53ad3b1..665515c7edae 100644 --- a/arch/x86/include/asm/svm.h +++ b/arch/x86/include/asm/svm.h @@ -278,6 +278,7 @@ enum avic_ipi_failure_cause { #define AVIC_HPA_MASK ~((0xFFFULL << 52) | 0xFFF) #define VMCB_AVIC_APIC_BAR_MASK 0xFFFFFFFFFF000ULL +#define SVM_SEV_FEAT_DEBUG_SWAP BIT(5) struct vmcb_seg { u16 selector; diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 4826e6cc611b..61f2cad1cbaf 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -389,6 +389,8 @@ static inline bool vmcb12_is_intercept(struct vmcb_ctrl_area_cached *control, u3 return test_bit(bit, (unsigned long *)&control->intercepts); } +extern bool sev_es_is_debug_swap_enabled(void); + static inline void set_dr_intercepts(struct vcpu_svm *svm) { struct vmcb *vmcb = svm->vmcb01.ptr; @@ -410,8 +412,10 @@ static inline void set_dr_intercepts(struct vcpu_svm *svm) vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE); } - vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); - vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); + if (!sev_es_guest(svm->vcpu.kvm) || !sev_es_is_debug_swap_enabled()) { + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); + } recalc_intercepts(svm); } @@ -422,8 +426,12 @@ static inline void clr_dr_intercepts(struct vcpu_svm *svm) vmcb->control.intercepts[INTERCEPT_DR] = 0; - /* DR7 access must remain intercepted for an SEV-ES guest */ - if (sev_es_guest(svm->vcpu.kvm)) { + /* + * DR7 access must remain intercepted for an SEV-ES guest unless DebugSwap + * (depends on NO_NESTED_DATA_BP) is enabled as otherwise a VM writing to DR7 + * from the #DB handler may trigger infinite loop of #DB's. + */ + if (sev_es_guest(svm->vcpu.kvm) && !sev_es_is_debug_swap_enabled()) { vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ); vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE); } diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 86d6897f4806..e989a6f4953d 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -21,6 +21,7 @@ #include #include #include +#include #include "mmu.h" #include "x86.h" @@ -52,11 +53,21 @@ module_param_named(sev, sev_enabled, bool, 0444); /* enable/disable SEV-ES support */ static bool sev_es_enabled = true; module_param_named(sev_es, sev_es_enabled, bool, 0444); + +/* enable/disable SEV-ES DebugSwap support */ +static bool sev_es_debug_swap_enabled = true; +module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0644); #else #define sev_enabled false #define sev_es_enabled false +#define sev_es_debug_swap false #endif /* CONFIG_KVM_AMD_SEV */ +bool sev_es_is_debug_swap_enabled(void) +{ + return sev_es_debug_swap_enabled; +} + static u8 sev_enc_bit; static DECLARE_RWSEM(sev_deactivate_lock); static DEFINE_MUTEX(sev_bitmap_lock); @@ -604,6 +615,9 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm) save->xss = svm->vcpu.arch.ia32_xss; save->dr6 = svm->vcpu.arch.dr6; + if (sev_es_is_debug_swap_enabled()) + save->sev_features |= SVM_SEV_FEAT_DEBUG_SWAP; + pr_debug("Virtual Machine Save Area (VMSA):\n"); print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false); @@ -2249,6 +2263,9 @@ void __init sev_hardware_setup(void) out: sev_enabled = sev_supported; sev_es_enabled = sev_es_supported; + if (sev_es_debug_swap_enabled) + sev_es_debug_swap_enabled = sev_es_enabled && + cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP); #endif } @@ -3027,6 +3044,18 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) /* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */ hostsa->xss = host_xss; + + /* The DebugSwap SEV feature does Type B swaps of DR[0-3] */ + if (sev_es_is_debug_swap_enabled()) { + hostsa->dr0 = native_get_debugreg(0); + hostsa->dr1 = native_get_debugreg(1); + hostsa->dr2 = native_get_debugreg(2); + hostsa->dr3 = native_get_debugreg(3); + hostsa->dr0_addr_mask = amd_get_dr_addr_mask(0); + hostsa->dr1_addr_mask = amd_get_dr_addr_mask(1); + hostsa->dr2_addr_mask = amd_get_dr_addr_mask(2); + hostsa->dr3_addr_mask = amd_get_dr_addr_mask(3); + } } void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 60c7c880266b..6c54a3c9d442 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1190,7 +1190,8 @@ static void init_vmcb(struct kvm_vcpu *vcpu) set_exception_intercept(svm, UD_VECTOR); set_exception_intercept(svm, MC_VECTOR); set_exception_intercept(svm, AC_VECTOR); - set_exception_intercept(svm, DB_VECTOR); + if (!sev_es_is_debug_swap_enabled()) + set_exception_intercept(svm, DB_VECTOR); /* * Guest access to VMware backdoor ports could legitimately * trigger #GP because of TSS I/O permission bitmap. -- 2.38.1