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Subject[RFC RESEND PATCH 5/6] x86/speculation, kvm: move guest FPU state into process local memory
Date
FPU registers contain guest data and must be protected from information
leak vulnerabilities in the kernel.

FPU register state for vCPUs are allocated from the globally-visible
kernel heap. Change this to use process-local memory instead and thus
prevent access (or prefetching) in any other context in the kernel.

Signed-off-by: Julian Stecklina <jsteckli@amazon.de>
---
arch/x86/include/asm/kvm_host.h | 10 +++++++-
arch/x86/kvm/x86.c | 42 ++++++++++++++++++++++-----------
2 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 55e51ff7e421..5dd29bfef77f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -36,6 +36,7 @@
#include <asm/asm.h>
#include <asm/kvm_page_track.h>
#include <asm/hyperv-tlfs.h>
+#include <asm/proclocal.h>

#define KVM_MAX_VCPUS 288
#define KVM_SOFT_MAX_VCPUS 240
@@ -530,7 +531,13 @@ struct kvm_vcpu_hv {
cpumask_t tlb_flush;
};

+struct kvm_vcpu_arch_hidden {
+ struct fpu guest_fpu;
+};
+
struct kvm_vcpu_arch {
+ struct proclocal hidden;
+
/*
* rip and regs accesses must go through
* kvm_{register,rip}_{read,write} functions.
@@ -611,7 +618,6 @@ struct kvm_vcpu_arch {
* host PRKU bits.
*/
struct fpu user_fpu;
- struct fpu guest_fpu;

u64 xcr0;
u64 guest_supported_xcr0;
@@ -1580,4 +1586,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
#define put_smstate(type, buf, offset, val) \
*(type *)((buf) + (offset) - 0x7e00) = val

+struct kvm_vcpu_arch_hidden *kvm_arch_vcpu_hidden_get(struct kvm_vcpu *vcpu);
+
#endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 66d66d77caee..941fa3209607 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -37,6 +37,7 @@
#include <linux/vmalloc.h>
#include <linux/export.h>
#include <linux/moduleparam.h>
+#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/highmem.h>
#include <linux/iommu.h>
@@ -69,6 +70,7 @@
#include <asm/irq_remapping.h>
#include <asm/mshyperv.h>
#include <asm/hypervisor.h>
+#include <asm/proclocal.h>

#define CREATE_TRACE_POINTS
#include "trace.h"
@@ -3630,7 +3632,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,

static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
{
- struct xregs_state *xsave = &vcpu->arch.guest_fpu.state.xsave;
+ struct xregs_state *xsave = &kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.xsave;
u64 xstate_bv = xsave->header.xfeatures;
u64 valid;

@@ -3672,7 +3674,7 @@ static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)

static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
{
- struct xregs_state *xsave = &vcpu->arch.guest_fpu.state.xsave;
+ struct xregs_state *xsave = &kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.xsave;
u64 xstate_bv = *(u64 *)(src + XSAVE_HDR_OFFSET);
u64 valid;

@@ -3720,7 +3722,7 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
fill_xsave((u8 *) guest_xsave->region, vcpu);
} else {
memcpy(guest_xsave->region,
- &vcpu->arch.guest_fpu.state.fxsave,
+ &kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.fxsave,
sizeof(struct fxregs_state));
*(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)] =
XFEATURE_MASK_FPSSE;
@@ -3750,7 +3752,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
if (xstate_bv & ~XFEATURE_MASK_FPSSE ||
mxcsr & ~mxcsr_feature_mask)
return -EINVAL;
- memcpy(&vcpu->arch.guest_fpu.state.fxsave,
+ memcpy(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.fxsave,
guest_xsave->region, sizeof(struct fxregs_state));
}
return 0;
@@ -7996,7 +7998,7 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
preempt_disable();
copy_fpregs_to_fpstate(&vcpu->arch.user_fpu);
/* PKRU is separately restored in kvm_x86_ops->run. */
- __copy_kernel_to_fpregs(&vcpu->arch.guest_fpu.state,
+ __copy_kernel_to_fpregs(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state,
~XFEATURE_MASK_PKRU);
preempt_enable();
trace_kvm_fpu(1);
@@ -8006,7 +8008,7 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
{
preempt_disable();
- copy_fpregs_to_fpstate(&vcpu->arch.guest_fpu);
+ copy_fpregs_to_fpstate(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu);
copy_kernel_to_fpregs(&vcpu->arch.user_fpu.state);
preempt_enable();
++vcpu->stat.fpu_reload;
@@ -8501,7 +8503,7 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)

vcpu_load(vcpu);

- fxsave = &vcpu->arch.guest_fpu.state.fxsave;
+ fxsave = &kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.fxsave;
memcpy(fpu->fpr, fxsave->st_space, 128);
fpu->fcw = fxsave->cwd;
fpu->fsw = fxsave->swd;
@@ -8521,8 +8523,7 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)

vcpu_load(vcpu);

- fxsave = &vcpu->arch.guest_fpu.state.fxsave;
-
+ fxsave = &kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.fxsave;
memcpy(fxsave->st_space, fpu->fpr, 128);
fxsave->cwd = fpu->fcw;
fxsave->swd = fpu->fsw;
@@ -8577,9 +8578,9 @@ static int sync_regs(struct kvm_vcpu *vcpu)

static void fx_init(struct kvm_vcpu *vcpu)
{
- fpstate_init(&vcpu->arch.guest_fpu.state);
+ fpstate_init(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state);
if (boot_cpu_has(X86_FEATURE_XSAVES))
- vcpu->arch.guest_fpu.state.xsave.header.xcomp_bv =
+ kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.xsave.header.xcomp_bv =
host_xcr0 | XSTATE_COMPACTION_ENABLED;

/*
@@ -8703,11 +8704,11 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
*/
if (init_event)
kvm_put_guest_fpu(vcpu);
- mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu.state.xsave,
+ mpx_state_buffer = get_xsave_addr(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.xsave,
XFEATURE_MASK_BNDREGS);
if (mpx_state_buffer)
memset(mpx_state_buffer, 0, sizeof(struct mpx_bndreg_state));
- mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu.state.xsave,
+ mpx_state_buffer = get_xsave_addr(&kvm_arch_vcpu_hidden_get(vcpu)->guest_fpu.state.xsave,
XFEATURE_MASK_BNDCSR);
if (mpx_state_buffer)
memset(mpx_state_buffer, 0, sizeof(struct mpx_bndcsr));
@@ -8892,11 +8893,21 @@ bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
struct static_key kvm_no_apic_vcpu __read_mostly;
EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu);

+struct kvm_vcpu_arch_hidden *kvm_arch_vcpu_hidden_get(struct kvm_vcpu *vcpu)
+{
+ return proclocal_get(&vcpu->arch.hidden, struct kvm_vcpu_arch_hidden);
+}
+EXPORT_SYMBOL_GPL(kvm_arch_vcpu_hidden_get);
+
int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
{
struct page *page;
int r;

+ r = kalloc_proclocal(&vcpu->arch.hidden, sizeof(struct kvm_vcpu_arch_hidden));
+ if (r)
+ goto fail;
+
vcpu->arch.apicv_active = kvm_x86_ops->get_enable_apicv(vcpu);
vcpu->arch.emulate_ctxt.ops = &emulate_ops;
if (!irqchip_in_kernel(vcpu->kvm) || kvm_vcpu_is_reset_bsp(vcpu))
@@ -8907,7 +8918,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page) {
r = -ENOMEM;
- goto fail;
+ goto fail_free_hidden;
}
vcpu->arch.pio_data = page_address(page);

@@ -8963,6 +8974,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
kvm_mmu_destroy(vcpu);
fail_free_pio_data:
free_page((unsigned long)vcpu->arch.pio_data);
+fail_free_hidden:
+ kfree_proclocal(&vcpu->arch.hidden);
fail:
return r;
}
@@ -8981,6 +8994,7 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
free_page((unsigned long)vcpu->arch.pio_data);
if (!lapic_in_kernel(vcpu))
static_key_slow_dec(&kvm_no_apic_vcpu);
+ kfree_proclocal(&vcpu->arch.hidden);
}

void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
--
2.17.1
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