From 5aea4096380f5b14e3c0345bdafc291e9ae6d8d1 Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Thu, 18 Sep 2025 09:55:05 -0700 Subject: [PATCH] KVM: arm64: nv: Allow userspace to de-feature stage-2 TGRANs KVM advertises the stage-2 TGRAN fields as writable to userspace but prevents any modification for NV-enabled VMs. Update the special-cased sanitization to permit de-featuring a particular TGRAN without allowing the legacy value which refers to the stage-1 field for support. Reported-by: Itaru Kitayama Signed-off-by: Oliver Upton Reviewed-by: Suzuki K Poulose Signed-off-by: Marc Zyngier --- arch/arm64/kvm/sys_regs.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index b29f72478a50d..83ecfdb467047 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -2148,16 +2148,29 @@ static int set_id_aa64pfr1_el1(struct kvm_vcpu *vcpu, return set_id_reg(vcpu, rd, user_val); } +/* + * Allow userspace to de-feature a stage-2 translation granule but prevent it + * from claiming the impossible. + */ +#define tgran2_val_allowed(tg, safe, user) \ +({ \ + u8 __s = SYS_FIELD_GET(ID_AA64MMFR0_EL1, tg, safe); \ + u8 __u = SYS_FIELD_GET(ID_AA64MMFR0_EL1, tg, user); \ + \ + __s == __u || __u == ID_AA64MMFR0_EL1_##tg##_NI; \ +}) + static int set_id_aa64mmfr0_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, u64 user_val) { u64 sanitized_val = kvm_read_sanitised_id_reg(vcpu, rd); - u64 tgran2_mask = ID_AA64MMFR0_EL1_TGRAN4_2_MASK | - ID_AA64MMFR0_EL1_TGRAN16_2_MASK | - ID_AA64MMFR0_EL1_TGRAN64_2_MASK; - if (vcpu_has_nv(vcpu) && - ((sanitized_val & tgran2_mask) != (user_val & tgran2_mask))) + if (!vcpu_has_nv(vcpu)) + return set_id_reg(vcpu, rd, user_val); + + if (!tgran2_val_allowed(TGRAN4_2, sanitized_val, user_val) || + !tgran2_val_allowed(TGRAN16_2, sanitized_val, user_val) || + !tgran2_val_allowed(TGRAN64_2, sanitized_val, user_val)) return -EINVAL; return set_id_reg(vcpu, rd, user_val); -- 2.47.3