This is a note to let you know that I've just added the patch titled KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-vmx-prevent-guest-rsb-poisoning-attacks-with-eibrs.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From stable-owner@xxxxxxxxxxxxxxx Thu Nov 17 10:22:26 2022 From: Suleiman Souhlal <suleiman@xxxxxxxxxx> Date: Thu, 17 Nov 2022 18:19:43 +0900 Subject: KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS To: stable@xxxxxxxxxxxxxxx Cc: x86@xxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, bp@xxxxxxxxx, pbonzini@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, jpoimboe@xxxxxxxxxx, cascardo@xxxxxxxxxxxxx, surajjs@xxxxxxxxxx, ssouhlal@xxxxxxxxxxx, suleiman@xxxxxxxxxx Message-ID: <20221117091952.1940850-26-suleiman@xxxxxxxxxx> From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> commit fc02735b14fff8c6678b521d324ade27b1a3d4cf upstream. On eIBRS systems, the returns in the vmexit return path from __vmx_vcpu_run() to vmx_vcpu_run() are exposed to RSB poisoning attacks. Fix that by moving the post-vmexit spec_ctrl handling to immediately after the vmexit. Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx> [ bp: Adjust for the fact that vmexit is in inline assembly ] Signed-off-by: Suraj Jitindar Singh <surajjs@xxxxxxxxxx> Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/nospec-branch.h | 3 +- arch/x86/kernel/cpu/bugs.c | 4 +++ arch/x86/kvm/vmx.c | 46 ++++++++++++++++++++++++++++++----- 3 files changed, 46 insertions(+), 7 deletions(-) --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -271,7 +271,7 @@ extern char __indirect_thunk_end[]; * retpoline and IBRS mitigations for Spectre v2 need this; only on future * CPUs with IBRS_ALL *might* it be avoided. */ -static inline void vmexit_fill_RSB(void) +static __always_inline void vmexit_fill_RSB(void) { #ifdef CONFIG_RETPOLINE unsigned long loops; @@ -306,6 +306,7 @@ static inline void indirect_branch_predi /* The Intel SPEC CTRL MSR base value cache */ extern u64 x86_spec_ctrl_base; +extern u64 x86_spec_ctrl_current; extern void write_spec_ctrl_current(u64 val, bool force); extern u64 spec_ctrl_current(void); --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -185,6 +185,10 @@ void __init check_bugs(void) #endif } +/* + * NOTE: For VMX, this function is not called in the vmexit path. + * It uses vmx_spec_ctrl_restore_host() instead. + */ void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) { --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -10760,10 +10760,31 @@ static void vmx_update_hv_timer(struct k vmx->loaded_vmcs->hv_timer_armed = false; } +u64 __always_inline vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx) +{ + u64 guestval, hostval = this_cpu_read(x86_spec_ctrl_current); + + if (!cpu_feature_enabled(X86_FEATURE_MSR_SPEC_CTRL)) + return 0; + + guestval = __rdmsr(MSR_IA32_SPEC_CTRL); + + /* + * If the guest/host SPEC_CTRL values differ, restore the host value. + */ + if (guestval != hostval) + native_wrmsrl(MSR_IA32_SPEC_CTRL, hostval); + + barrier_nospec(); + + return guestval; +} + static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) { struct vcpu_vmx *vmx = to_vmx(vcpu); unsigned long cr3, cr4, evmcs_rsp; + u64 spec_ctrl; /* Record the guest's net vcpu time for enforced NMI injections. */ if (unlikely(!enable_vnmi && @@ -10989,6 +11010,24 @@ static void __noclone vmx_vcpu_run(struc #endif ); + /* + * IMPORTANT: RSB filling and SPEC_CTRL handling must be done before + * the first unbalanced RET after vmexit! + * + * For retpoline, RSB filling is needed to prevent poisoned RSB entries + * and (in some cases) RSB underflow. + * + * eIBRS has its own protection against poisoned RSB, so it doesn't + * need the RSB filling sequence. But it does need to be enabled + * before the first unbalanced RET. + * + * So no RETs before vmx_spec_ctrl_restore_host() below. + */ + vmexit_fill_RSB(); + + /* Save this for below */ + spec_ctrl = vmx_spec_ctrl_restore_host(vmx); + vmx_enable_fb_clear(vmx); /* @@ -11007,12 +11046,7 @@ static void __noclone vmx_vcpu_run(struc * save it. */ if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))) - vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL); - - x86_spec_ctrl_restore_host(vmx->spec_ctrl, 0); - - /* Eliminate branch target predictions from guest mode */ - vmexit_fill_RSB(); + vmx->spec_ctrl = spec_ctrl; /* All fields are clean at this point */ if (static_branch_unlikely(&enable_evmcs)) Patches currently in stable-queue which might be from stable-owner@xxxxxxxxxxxxxxx are queue-4.19/x86-speculation-disable-rrsba-behavior.patch queue-4.19/revert-x86-speculation-add-rsb-vm-exit-protections.patch queue-4.19/kvm-vmx-fix-ibrs-handling-after-vmexit.patch queue-4.19/kvm-vmx-prevent-guest-rsb-poisoning-attacks-with-eibrs.patch queue-4.19/x86-cpufeature-add-facility-to-check-for-min-microcode-revisions.patch queue-4.19/x86-bugs-keep-a-per-cpu-ia32_spec_ctrl-value.patch queue-4.19/x86-cpu-amd-enumerate-btc_no.patch queue-4.19/x86-speculation-fix-firmware-entry-spec_ctrl-handling.patch queue-4.19/x86-speculation-add-spectre_v2-ibrs-option-to-support-kernel-ibrs.patch queue-4.19/x86-cpu-add-consistent-cpu-match-macros.patch queue-4.19/x86-speculation-remove-x86_spec_ctrl_mask.patch queue-4.19/x86-bugs-add-cannon-lake-to-retbleed-affected-cpu-list.patch queue-4.19/x86-bugs-warn-when-ibrs-mitigation-is-selected-on-enhanced-ibrs-parts.patch queue-4.19/x86-speculation-fill-rsb-on-vmexit-for-ibrs.patch queue-4.19/x86-cpu-add-a-steppings-field-to-struct-x86_cpu_id.patch queue-4.19/x86-common-stamp-out-the-stepping-madness.patch queue-4.19/x86-bugs-split-spectre_v2_select_mitigation-and-spectre_v2_user_select_mitigation.patch queue-4.19/x86-bugs-report-intel-retbleed-vulnerability.patch queue-4.19/x86-speculation-change-fill_return_buffer-to-work-with-objtool.patch queue-4.19/x86-cpufeatures-move-retpoline-flags-to-word-11.patch queue-4.19/x86-speculation-fix-spec_ctrl-write-on-smt-state-change.patch queue-4.19/x86-bugs-optimize-spec_ctrl-msr-writes.patch queue-4.19/x86-bugs-report-amd-retbleed-vulnerability.patch queue-4.19/x86-speculation-fix-rsb-filling-with-config_retpoline-n.patch queue-4.19/x86-cpufeature-fix-various-quality-problems-in-the-asm-cpu_device_hd.h-header.patch queue-4.19/intel_idle-disable-ibrs-during-long-idle.patch queue-4.19/x86-speculation-use-declare_per_cpu-for-x86_spec_ctrl_current.patch queue-4.19/x86-entry-remove-skip_r11rcx.patch queue-4.19/x86-speculation-use-cached-host-spec_ctrl-value-for-guest-entry-exit.patch queue-4.19/x86-devicetable-move-x86-specific-macro-out-of-generic-code.patch queue-4.19/x86-bugs-add-amd-retbleed-boot-parameter.patch queue-4.19/x86-entry-add-kernel-ibrs-implementation.patch queue-4.19/revert-x86-cpu-add-a-steppings-field-to-struct-x86_cpu_id.patch queue-4.19/x86-speculation-add-rsb-vm-exit-protections.patch