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Subject[RFC 10/10] kvm, x86: 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: Marius Hillenbrand <mhillenb@amazon.de>
Inspired-by: Julian Stecklina <js@alien8.de> (while jsteckli@amazon.de)
Cc: Alexander Graf <graf@amazon.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/include/asm/kvm_host.h | 8 ++++++++
arch/x86/kvm/x86.c | 24 ++++++++++++------------
2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4896ecde1c11..b3574217b011 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
@@ -545,6 +546,7 @@ struct kvm_vcpu_arch_hidden {
* kvm_{register,rip}_{read,write} functions.
*/
kvm_arch_regs_t regs;
+ struct fpu guest_fpu;
};
#endif

@@ -631,9 +633,15 @@ struct kvm_vcpu_arch {
* it is switched out separately at VMENTER and VMEXIT time. The
* "guest_fpu" state here contains the guest FPU context, with the
* host PRKU bits.
+ *
+ * With process-local memory, the guest FPU state will be hidden in
+ * kvm_vcpu_arch_hidden. Thus, access to this struct must go through
+ * kvm_vcpu_arch_state(vcpu).
*/
struct fpu user_fpu;
+#ifndef CONFIG_KVM_PROCLOCAL
struct fpu guest_fpu;
+#endif

u64 xcr0;
u64 guest_supported_xcr0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35e41a772807..480b4ed438ae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3792,7 +3792,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.xsave;
u64 xstate_bv = xsave->header.xfeatures;
u64 valid;

@@ -3834,7 +3834,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.xsave;
u64 xstate_bv = *(u64 *)(src + XSAVE_HDR_OFFSET);
u64 valid;

@@ -3882,7 +3882,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.fxsave,
sizeof(struct fxregs_state));
*(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)] =
XFEATURE_MASK_FPSSE;
@@ -3912,7 +3912,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.fxsave,
guest_xsave->region, sizeof(struct fxregs_state));
}
return 0;
@@ -8302,7 +8302,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state,
~XFEATURE_MASK_PKRU);
preempt_enable();
trace_kvm_fpu(1);
@@ -8312,7 +8312,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu);
copy_kernel_to_fpregs(&vcpu->arch.user_fpu.state);
preempt_enable();
++vcpu->stat.fpu_reload;
@@ -8807,7 +8807,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.fxsave;
memcpy(fpu->fpr, fxsave->st_space, 128);
fpu->fcw = fxsave->cwd;
fpu->fsw = fxsave->swd;
@@ -8827,7 +8827,7 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.fxsave;

memcpy(fxsave->st_space, fpu->fpr, 128);
fxsave->cwd = fpu->fcw;
@@ -8883,9 +8883,9 @@ 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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state);
if (boot_cpu_has(X86_FEATURE_XSAVES))
- vcpu->arch.guest_fpu.state.xsave.header.xcomp_bv =
+ kvm_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.xsave.header.xcomp_bv =
host_xcr0 | XSTATE_COMPACTION_ENABLED;

/*
@@ -9009,11 +9009,11 @@ 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_vcpu_arch_state(&vcpu->arch)->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_vcpu_arch_state(&vcpu->arch)->guest_fpu.state.xsave,
XFEATURE_MASK_BNDCSR);
if (mpx_state_buffer)
memset(mpx_state_buffer, 0, sizeof(struct mpx_bndcsr));
--
2.21.0
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