6d825fcff3
This improves compatibility for guests w.r.t. live-migration, or live
snapshot rollback, to hosts with less (FPU) xfeatures supported, as
long as the set of features that was actually exposed to the guest is
still supported.
This improves on the ad856280ddea ("x86/kvm/fpu: Limit guest
user_xfeatures to supported bits of XCR0") bug fix.
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
165 lines
6.9 KiB
Diff
165 lines
6.9 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Sean Christopherson <seanjc@google.com>
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Date: Wed, 27 Sep 2023 17:19:52 -0700
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Subject: [PATCH] x86/fpu: Allow caller to constrain xfeatures when copying to
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uabi buffer
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Plumb an xfeatures mask into __copy_xstate_to_uabi_buf() so that KVM can
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constrain which xfeatures are saved into the userspace buffer without
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having to modify the user_xfeatures field in KVM's guest_fpu state.
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KVM's ABI for KVM_GET_XSAVE{2} is that features that are not exposed to
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guest must not show up in the effective xstate_bv field of the buffer.
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Saving only the guest-supported xfeatures allows userspace to load the
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saved state on a different host with a fewer xfeatures, so long as the
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target host supports the xfeatures that are exposed to the guest.
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KVM currently sets user_xfeatures directly to restrict KVM_GET_XSAVE{2} to
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the set of guest-supported xfeatures, but doing so broke KVM's historical
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ABI for KVM_SET_XSAVE, which allows userspace to load any xfeatures that
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are supported by the *host*.
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Cc: stable@vger.kernel.org
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Signed-off-by: Sean Christopherson <seanjc@google.com>
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Message-Id: <20230928001956.924301-2-seanjc@google.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit 18164f66e6c59fda15c198b371fa008431efdb22)
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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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---
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arch/x86/include/asm/fpu/api.h | 3 ++-
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arch/x86/kernel/fpu/core.c | 5 +++--
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arch/x86/kernel/fpu/xstate.c | 7 +++++--
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arch/x86/kernel/fpu/xstate.h | 3 ++-
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arch/x86/kvm/x86.c | 21 +++++++++------------
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5 files changed, 21 insertions(+), 18 deletions(-)
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diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
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index b475d9a582b8..e829fa4c6788 100644
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--- a/arch/x86/include/asm/fpu/api.h
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+++ b/arch/x86/include/asm/fpu/api.h
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@@ -148,7 +148,8 @@ static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) {
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static inline void fpu_sync_guest_vmexit_xfd_state(void) { }
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#endif
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-extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
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+extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
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+ unsigned int size, u64 xfeatures, u32 pkru);
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extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
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static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
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diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
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index caf33486dc5e..cddd5018e6a4 100644
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--- a/arch/x86/kernel/fpu/core.c
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+++ b/arch/x86/kernel/fpu/core.c
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@@ -369,14 +369,15 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
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EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
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void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
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- unsigned int size, u32 pkru)
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+ unsigned int size, u64 xfeatures, u32 pkru)
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{
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struct fpstate *kstate = gfpu->fpstate;
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union fpregs_state *ustate = buf;
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struct membuf mb = { .p = buf, .left = size };
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if (cpu_feature_enabled(X86_FEATURE_XSAVE)) {
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- __copy_xstate_to_uabi_buf(mb, kstate, pkru, XSTATE_COPY_XSAVE);
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+ __copy_xstate_to_uabi_buf(mb, kstate, xfeatures, pkru,
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+ XSTATE_COPY_XSAVE);
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} else {
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memcpy(&ustate->fxsave, &kstate->regs.fxsave,
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sizeof(ustate->fxsave));
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diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
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index 1afbc4866b10..463ec0cd0dab 100644
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--- a/arch/x86/kernel/fpu/xstate.c
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+++ b/arch/x86/kernel/fpu/xstate.c
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@@ -1053,6 +1053,7 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
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* __copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
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* @to: membuf descriptor
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* @fpstate: The fpstate buffer from which to copy
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+ * @xfeatures: The mask of xfeatures to save (XSAVE mode only)
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* @pkru_val: The PKRU value to store in the PKRU component
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* @copy_mode: The requested copy mode
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*
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@@ -1063,7 +1064,8 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
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* It supports partial copy but @to.pos always starts from zero.
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*/
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void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
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- u32 pkru_val, enum xstate_copy_mode copy_mode)
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+ u64 xfeatures, u32 pkru_val,
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+ enum xstate_copy_mode copy_mode)
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{
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const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr);
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struct xregs_state *xinit = &init_fpstate.regs.xsave;
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@@ -1087,7 +1089,7 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
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break;
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case XSTATE_COPY_XSAVE:
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- header.xfeatures &= fpstate->user_xfeatures;
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+ header.xfeatures &= fpstate->user_xfeatures & xfeatures;
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break;
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}
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@@ -1189,6 +1191,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
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enum xstate_copy_mode copy_mode)
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{
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__copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate,
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+ tsk->thread.fpu.fpstate->user_xfeatures,
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tsk->thread.pkru, copy_mode);
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}
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diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
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index a4ecb04d8d64..3518fb26d06b 100644
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--- a/arch/x86/kernel/fpu/xstate.h
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+++ b/arch/x86/kernel/fpu/xstate.h
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@@ -43,7 +43,8 @@ enum xstate_copy_mode {
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struct membuf;
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extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
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- u32 pkru_val, enum xstate_copy_mode copy_mode);
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+ u64 xfeatures, u32 pkru_val,
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+ enum xstate_copy_mode copy_mode);
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extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
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enum xstate_copy_mode mode);
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extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru);
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index ff92ff41d5ce..a43a950d04cb 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -5314,26 +5314,23 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
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return 0;
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}
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-static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
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- struct kvm_xsave *guest_xsave)
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+
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+static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
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+ u8 *state, unsigned int size)
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{
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if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
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return;
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- fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
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- guest_xsave->region,
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- sizeof(guest_xsave->region),
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+ fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, state, size,
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+ vcpu->arch.guest_fpu.fpstate->user_xfeatures,
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vcpu->arch.pkru);
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}
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-static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
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- u8 *state, unsigned int size)
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+static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
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+ struct kvm_xsave *guest_xsave)
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{
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- if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
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- return;
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-
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- fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
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- state, size, vcpu->arch.pkru);
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+ return kvm_vcpu_ioctl_x86_get_xsave2(vcpu, (void *)guest_xsave->region,
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+ sizeof(guest_xsave->region));
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}
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static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
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