[v2,21/24] KVM: arm64: Maintain a copy of 'kvm_arm_vmid_bits' at EL2

Commit Message

Will Deacon June 30, 2022, 1:57 p.m. UTC

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' and initialise it from the host value
while it is still trusted.

Signed-off-by: Will Deacon <[e-mail]>
---
 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(-)

Patch

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 37a2d833851a..3e2489d23ff0 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -80,9 +80,6 @@  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);
-
 /* Kernel symbols needed for cpus_have_final/const_caps checks. */
 KVM_NVHE_ALIAS(arm64_const_caps_ready);
 KVM_NVHE_ALIAS(cpu_hwcap_keys);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 1934fcb2c2d3..fe249b584115 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1901,6 +1901,7 @@  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 a4a518b2a43b..571334fd58ff 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.
  */