[PATCH v4 22/25] KVM: arm64: Maintain a copy of 'kvm_arm_vmid_bits' at EL2

Will Deacon
2022-10-17T12:05:48Z

Sharing 'kvm_arm_vmid_bits' between EL1 and EL2 allows the host to
modify the variable arbitrarily, potentially leading to all sorts of
shenanians as this is used to configure the VTTBR register for the
guest stage-2.

In preparation for unmapping host sections entirely from EL2, maintain
a copy of 'kvm_arm_vmid_bits' in the pKVM hypervisor and initialise it
from the host value while it is still trusted.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_hyp.h | 2 ++
arch/arm64/kernel/image-vars.h | 3 ---
arch/arm64/kvm/arm.c | 1 +
arch/arm64/kvm/hyp/nvhe/pkvm.c | 3 +++
4 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index fd99cf09972d..6797eafe7890 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -124,4 +124,6 @@ extern u64 kvm_nvhe_sym(id_aa64mmfr1_el1_sys_val);
extern u64 kvm_nvhe_sym(id_aa64mmfr2_el1_sys_val);

extern unsigned long kvm_nvhe_sym(__icache_flags);
+extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits);
+
#endif /* __ARM64_KVM_HYP_H__ */
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index ae8f37f4aa8c..31ad75da4d58 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -71,9 +71,6 @@ KVM_NVHE_ALIAS(nvhe_hyp_panic_handler);
/* Vectors installed by hyp-init on reset HVC. */
KVM_NVHE_ALIAS(__hyp_stub_vectors);

-/* VMID bits set by the KVM VMID allocator */
-KVM_NVHE_ALIAS(kvm_arm_vmid_bits);
-
/* Static keys which are set if a vGIC trap should be handled in hyp. */
KVM_NVHE_ALIAS(vgic_v2_cpuif_trap);
KVM_NVHE_ALIAS(vgic_v3_cpuif_trap);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 25467f24803d..1d4b8122d010 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1893,6 +1893,7 @@ static void kvm_hyp_init_symbols(void)
kvm_nvhe_sym(id_aa64mmfr1_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
kvm_nvhe_sym(id_aa64mmfr2_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64MMFR2_EL1);
kvm_nvhe_sym(__icache_flags) = __icache_flags;
+ kvm_nvhe_sym(kvm_arm_vmid_bits) = kvm_arm_vmid_bits;
}

static int kvm_hyp_init_protection(u32 hyp_va_bits)
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index f5f300cc5864..826335ccad9d 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -15,6 +15,9 @@
/* Used by icache_is_vpipt(). */
unsigned long __icache_flags;

+/* Used by kvm_get_vttbr(). */
+unsigned int kvm_arm_vmid_bits;
+
/*
* Set trap register values based on features in ID_AA64PFR0.
*/
--
2.38.0.413.g74048e4d9e-goog