From 9f2febf3f04daebdaaa5a43cfa20e3844905c0f9 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 30 Sep 2022 14:24:40 -0400 Subject: KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Restoration of the host IA32_SPEC_CTRL value is probably too late with respect to the return thunk training sequence. With respect to the user/kernel boundary, AMD says, "If software chooses to toggle STIBP (e.g., set STIBP on kernel entry, and clear it on kernel exit), software should set STIBP to 1 before executing the return thunk training sequence." I assume the same requirements apply to the guest/host boundary. The return thunk training sequence is in vmenter.S, quite close to the VM-exit. On hosts without V_SPEC_CTRL, however, the host's IA32_SPEC_CTRL value is not restored until much later. To avoid this, move the restoration of host SPEC_CTRL to assembly and, for consistency, move the restoration of the guest SPEC_CTRL as well. This is not particularly difficult, apart from some care to cover both 32- and 64-bit, and to share code between SEV-ES and normal vmentry. Cc: stable@vger.kernel.org Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk") Suggested-by: Jim Mattson Reviewed-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- arch/x86/kernel/cpu/bugs.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) (limited to 'arch/x86/kernel/cpu/bugs.c') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index da7c361f47e0..6ec0b7ce7453 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -196,22 +196,15 @@ void __init check_bugs(void) } /* - * NOTE: This function is *only* called for SVM. VMX spec_ctrl handling is - * done in vmenter.S. + * NOTE: This function is *only* called for SVM, since Intel uses + * MSR_IA32_SPEC_CTRL for SSBD. */ void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) { - u64 msrval, guestval = guest_spec_ctrl, hostval = spec_ctrl_current(); + u64 guestval, hostval; struct thread_info *ti = current_thread_info(); - if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) { - if (hostval != guestval) { - msrval = setguest ? guestval : hostval; - wrmsrl(MSR_IA32_SPEC_CTRL, msrval); - } - } - /* * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported. -- cgit v1.2.3 From bd3d394e367e66e773a6cb25a82c29b04464230b Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 30 Sep 2022 14:48:24 -0400 Subject: x86, KVM: remove unnecessary argument to x86_virt_spec_ctrl and callers x86_virt_spec_ctrl only deals with the paravirtualized MSR_IA32_VIRT_SPEC_CTRL now and does not handle MSR_IA32_SPEC_CTRL anymore; remove the corresponding, unused argument. Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/spec-ctrl.h | 10 +++++----- arch/x86/kernel/cpu/bugs.c | 2 +- arch/x86/kvm/svm/svm.c | 4 ++-- 3 files changed, 8 insertions(+), 8 deletions(-) (limited to 'arch/x86/kernel/cpu/bugs.c') diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h index 5393babc0598..cb0386fc4dc3 100644 --- a/arch/x86/include/asm/spec-ctrl.h +++ b/arch/x86/include/asm/spec-ctrl.h @@ -13,7 +13,7 @@ * Takes the guest view of SPEC_CTRL MSR as a parameter and also * the guest's version of VIRT_SPEC_CTRL, if emulated. */ -extern void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool guest); +extern void x86_virt_spec_ctrl(u64 guest_virt_spec_ctrl, bool guest); /** * x86_spec_ctrl_set_guest - Set speculation control registers for the guest @@ -24,9 +24,9 @@ extern void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bo * Avoids writing to the MSR if the content/bits are the same */ static inline -void x86_spec_ctrl_set_guest(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl) +void x86_spec_ctrl_set_guest(u64 guest_virt_spec_ctrl) { - x86_virt_spec_ctrl(guest_spec_ctrl, guest_virt_spec_ctrl, true); + x86_virt_spec_ctrl(guest_virt_spec_ctrl, true); } /** @@ -38,9 +38,9 @@ void x86_spec_ctrl_set_guest(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl) * Avoids writing to the MSR if the content/bits are the same */ static inline -void x86_spec_ctrl_restore_host(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl) +void x86_spec_ctrl_restore_host(u64 guest_virt_spec_ctrl) { - x86_virt_spec_ctrl(guest_spec_ctrl, guest_virt_spec_ctrl, false); + x86_virt_spec_ctrl(guest_virt_spec_ctrl, false); } /* AMD specific Speculative Store Bypass MSR data */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 6ec0b7ce7453..3e3230cccaa7 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -200,7 +200,7 @@ void __init check_bugs(void) * MSR_IA32_SPEC_CTRL for SSBD. */ void -x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) +x86_virt_spec_ctrl(u64 guest_virt_spec_ctrl, bool setguest) { u64 guestval, hostval; struct thread_info *ti = current_thread_info(); diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index cf1aed25f4ab..9f88c8e6766e 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3984,7 +3984,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu) * being speculatively taken. */ if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL)) - x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl); + x86_spec_ctrl_set_guest(svm->virt_spec_ctrl); svm_vcpu_enter_exit(vcpu, spec_ctrl_intercepted); @@ -3992,7 +3992,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu) reload_tss(vcpu); if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL)) - x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl); + x86_spec_ctrl_restore_host(svm->virt_spec_ctrl); if (!sev_es_guest(vcpu->kvm)) { vcpu->arch.cr2 = svm->vmcb->save.cr2; -- cgit v1.2.3 From 66065157420c5b9b3f078f43d313c153e1ff7f83 Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Wed, 30 Nov 2022 07:25:51 -0800 Subject: x86/bugs: Make sure MSR_SPEC_CTRL is updated properly upon resume from S3 The "force" argument to write_spec_ctrl_current() is currently ambiguous as it does not guarantee the MSR write. This is due to the optimization that writes to the MSR happen only when the new value differs from the cached value. This is fine in most cases, but breaks for S3 resume when the cached MSR value gets out of sync with the hardware MSR value due to S3 resetting it. When x86_spec_ctrl_current is same as x86_spec_ctrl_base, the MSR write is skipped. Which results in SPEC_CTRL mitigations not getting restored. Move the MSR write from write_spec_ctrl_current() to a new function that unconditionally writes to the MSR. Update the callers accordingly and rename functions. [ bp: Rework a bit. ] Fixes: caa0ff24d5d0 ("x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value") Suggested-by: Borislav Petkov Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Thomas Gleixner Cc: Link: https://lore.kernel.org/r/806d39b0bfec2fe8f50dc5446dff20f5bb24a959.1669821572.git.pawan.kumar.gupta@linux.intel.com Signed-off-by: Linus Torvalds --- arch/x86/include/asm/nospec-branch.h | 2 +- arch/x86/kernel/cpu/bugs.c | 21 ++++++++++++++------- arch/x86/kernel/process.c | 2 +- 3 files changed, 16 insertions(+), 9 deletions(-) (limited to 'arch/x86/kernel/cpu/bugs.c') diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index c936ce9f0c47..dfdb103ae4f6 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -321,7 +321,7 @@ static inline void indirect_branch_prediction_barrier(void) /* The Intel SPEC CTRL MSR base value cache */ extern u64 x86_spec_ctrl_base; DECLARE_PER_CPU(u64, x86_spec_ctrl_current); -extern void write_spec_ctrl_current(u64 val, bool force); +extern void update_spec_ctrl_cond(u64 val); extern u64 spec_ctrl_current(void); /* diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 3e3230cccaa7..6daf84229548 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -60,11 +60,18 @@ EXPORT_SYMBOL_GPL(x86_spec_ctrl_current); static DEFINE_MUTEX(spec_ctrl_mutex); +/* Update SPEC_CTRL MSR and its cached copy unconditionally */ +static void update_spec_ctrl(u64 val) +{ + this_cpu_write(x86_spec_ctrl_current, val); + wrmsrl(MSR_IA32_SPEC_CTRL, val); +} + /* * Keep track of the SPEC_CTRL MSR value for the current task, which may differ * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update(). */ -void write_spec_ctrl_current(u64 val, bool force) +void update_spec_ctrl_cond(u64 val) { if (this_cpu_read(x86_spec_ctrl_current) == val) return; @@ -75,7 +82,7 @@ void write_spec_ctrl_current(u64 val, bool force) * When KERNEL_IBRS this MSR is written on return-to-user, unless * forced the update can be delayed until that time. */ - if (force || !cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) + if (!cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) wrmsrl(MSR_IA32_SPEC_CTRL, val); } @@ -1328,7 +1335,7 @@ static void __init spec_ctrl_disable_kernel_rrsba(void) if (ia32_cap & ARCH_CAP_RRSBA) { x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S; - write_spec_ctrl_current(x86_spec_ctrl_base, true); + update_spec_ctrl(x86_spec_ctrl_base); } } @@ -1450,7 +1457,7 @@ static void __init spectre_v2_select_mitigation(void) if (spectre_v2_in_ibrs_mode(mode)) { x86_spec_ctrl_base |= SPEC_CTRL_IBRS; - write_spec_ctrl_current(x86_spec_ctrl_base, true); + update_spec_ctrl(x86_spec_ctrl_base); } switch (mode) { @@ -1564,7 +1571,7 @@ static void __init spectre_v2_select_mitigation(void) static void update_stibp_msr(void * __unused) { u64 val = spec_ctrl_current() | (x86_spec_ctrl_base & SPEC_CTRL_STIBP); - write_spec_ctrl_current(val, true); + update_spec_ctrl(val); } /* Update x86_spec_ctrl_base in case SMT state changed. */ @@ -1797,7 +1804,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void) x86_amd_ssb_disable(); } else { x86_spec_ctrl_base |= SPEC_CTRL_SSBD; - write_spec_ctrl_current(x86_spec_ctrl_base, true); + update_spec_ctrl(x86_spec_ctrl_base); } } @@ -2048,7 +2055,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) void x86_spec_ctrl_setup_ap(void) { if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) - write_spec_ctrl_current(x86_spec_ctrl_base, true); + update_spec_ctrl(x86_spec_ctrl_base); if (ssb_mode == SPEC_STORE_BYPASS_DISABLE) x86_amd_ssb_disable(); diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index c21b7347a26d..e436c9c1ef3b 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -600,7 +600,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp, } if (updmsr) - write_spec_ctrl_current(msr, false); + update_spec_ctrl_cond(msr); } static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk) -- cgit v1.2.3