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KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM

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When running in protected mode we don't want to leak protected
guest state to the host, including whether a guest has used
fpsimd/sve. Therefore, eagerly restore the host state on guest
exit when running in protected mode, which happens only if the
guest has used fpsimd/sve.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20240603122852.3923848-7-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Fuad Tabba 2024-06-03 13:28:48 +01:00 committed by Marc Zyngier
parent 66d5b53e20
commit b5b9955617
4 changed files with 93 additions and 5 deletions
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13
arch/arm64/kvm/hyp/include/hyp/switch.h
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@ -321,6 +321,17 @@ static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
write_sysreg_el1(__vcpu_sys_reg(vcpu, ZCR_EL1), SYS_ZCR);
}
static inline void __hyp_sve_save_host(void)
{
struct cpu_sve_state *sve_state = *host_data_ptr(sve_state);
sve_state->zcr_el1 = read_sysreg_el1(SYS_ZCR);
write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
__sve_save_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
&sve_state->fpsr,
true);
}
static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu);
/*
@ -355,7 +366,7 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
/* Valid trap. Switch the context: */
/* First disable enough traps to allow us to update the registers */
if (sve_guest)
if (sve_guest || (is_protected_kvm_enabled() && system_supports_sve()))
cpacr_clear_set(0, CPACR_ELx_FPEN | CPACR_ELx_ZEN);
else
cpacr_clear_set(0, CPACR_ELx_FPEN);

67
arch/arm64/kvm/hyp/nvhe/hyp-main.c
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@ -23,20 +23,80 @@ DEFINE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
void __kvm_hyp_host_forward_smc(struct kvm_cpu_context *host_ctxt);
static void __hyp_sve_save_guest(struct kvm_vcpu *vcpu)
{
__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
/*
* On saving/restoring guest sve state, always use the maximum VL for
* the guest. The layout of the data when saving the sve state depends
* on the VL, so use a consistent (i.e., the maximum) guest VL.
*/
sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1, SYS_ZCR_EL2);
__sve_save_state(vcpu_sve_pffr(vcpu), &vcpu->arch.ctxt.fp_regs.fpsr, true);
write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
}
static void __hyp_sve_restore_host(void)
{
struct cpu_sve_state *sve_state = *host_data_ptr(sve_state);
/*
* On saving/restoring host sve state, always use the maximum VL for
* the host. The layout of the data when saving the sve state depends
* on the VL, so use a consistent (i.e., the maximum) host VL.
*
* Setting ZCR_EL2 to ZCR_ELx_LEN_MASK sets the effective length
* supported by the system (or limited at EL3).
*/
write_sysreg_s(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
__sve_restore_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
&sve_state->fpsr,
true);
write_sysreg_el1(sve_state->zcr_el1, SYS_ZCR);
}
static void fpsimd_sve_flush(void)
{
*host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
}
static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
{
if (!guest_owns_fp_regs())
return;
cpacr_clear_set(0, CPACR_ELx_FPEN | CPACR_ELx_ZEN);
isb();
if (vcpu_has_sve(vcpu))
__hyp_sve_save_guest(vcpu);
else
__fpsimd_save_state(&vcpu->arch.ctxt.fp_regs);
if (system_supports_sve())
__hyp_sve_restore_host();
else
__fpsimd_restore_state(*host_data_ptr(fpsimd_state));
*host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
}
static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
{
struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu;
fpsimd_sve_flush();
hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt;
hyp_vcpu->vcpu.arch.sve_state = kern_hyp_va(host_vcpu->arch.sve_state);
hyp_vcpu->vcpu.arch.sve_max_vl = host_vcpu->arch.sve_max_vl;
/* Limit guest vector length to the maximum supported by the host. */
hyp_vcpu->vcpu.arch.sve_max_vl = min(host_vcpu->arch.sve_max_vl, kvm_host_sve_max_vl);
hyp_vcpu->vcpu.arch.hw_mmu = host_vcpu->arch.hw_mmu;
hyp_vcpu->vcpu.arch.hcr_el2 = host_vcpu->arch.hcr_el2;
hyp_vcpu->vcpu.arch.mdcr_el2 = host_vcpu->arch.mdcr_el2;
hyp_vcpu->vcpu.arch.cptr_el2 = host_vcpu->arch.cptr_el2;
hyp_vcpu->vcpu.arch.iflags = host_vcpu->arch.iflags;
@ -54,10 +114,11 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
struct vgic_v3_cpu_if *host_cpu_if = &host_vcpu->arch.vgic_cpu.vgic_v3;
unsigned int i;
fpsimd_sve_sync(&hyp_vcpu->vcpu);
host_vcpu->arch.ctxt = hyp_vcpu->vcpu.arch.ctxt;
host_vcpu->arch.hcr_el2 = hyp_vcpu->vcpu.arch.hcr_el2;
host_vcpu->arch.cptr_el2 = hyp_vcpu->vcpu.arch.cptr_el2;
host_vcpu->arch.fault = hyp_vcpu->vcpu.arch.fault;

2
arch/arm64/kvm/hyp/nvhe/pkvm.c
View File

@ -588,6 +588,8 @@ unlock:
if (ret)
unmap_donated_memory(hyp_vcpu, sizeof(*hyp_vcpu));
hyp_vcpu->vcpu.arch.cptr_el2 = kvm_get_reset_cptr_el2(&hyp_vcpu->vcpu);
return ret;
}

16
arch/arm64/kvm/hyp/nvhe/switch.c
View File

@ -184,7 +184,21 @@ static bool kvm_handle_pvm_sys64(struct kvm_vcpu *vcpu, u64 *exit_code)
static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
{
__fpsimd_save_state(*host_data_ptr(fpsimd_state));
/*
* Non-protected kvm relies on the host restoring its sve state.
* Protected kvm restores the host's sve state as not to reveal that
* fpsimd was used by a guest nor leak upper sve bits.
*/
if (unlikely(is_protected_kvm_enabled() && system_supports_sve())) {
__hyp_sve_save_host();
/* Re-enable SVE traps if not supported for the guest vcpu. */
if (!vcpu_has_sve(vcpu))
cpacr_clear_set(CPACR_ELx_ZEN, 0);
} else {
__fpsimd_save_state(*host_data_ptr(fpsimd_state));
}
}
static const exit_handler_fn hyp_exit_handlers[] = {