Hi Dave, On Tue, Mar 19, 2019 at 11:26 PM Dave Martin <Dave.Martin@xxxxxxx> wrote: > > Some optional features of the Arm architecture add new system > registers that are not present in the base architecture. > > Where these features are optional for the guest, the visibility of > these registers may need to depend on some runtime configuration, > such as a flag passed to KVM_ARM_VCPU_INIT. > > For example, ZCR_EL1 and ID_AA64ZFR0_EL1 need to be hidden if SVE > is not enabled for the guest, even though these registers may be > present in the hardware and visible to the host at EL2. > > Adding special-case checks all over the place for individual > registers is going to get messy as the number of conditionally- > visible registers grows. > > In order to help solve this problem, this patch adds a new sysreg > method visibility() that can be used to hook in any needed runtime > visibility checks. This method can currently return > REG_HIDDEN_USER to inhibit enumeration and ioctl access to the > register for userspace, and REG_HIDDEN_GUEST to inhibit runtime > access by the guest using MSR/MRS. Wrappers are added to allow > these flags to be conveniently queried. > > This approach allows a conditionally modified view of individual > system registers such as the CPU ID registers, in addition to > completely hiding register where appropriate. > > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> I used 2 of your patches in my patch series on KVM guest for pointer authentication [1]. So for these 2 patches, [PATCH v6 11/27] KVM: arm64: Support runtime sysreg visibility filtering [PATCH v6 10/27] KVM: arm64: Propagate vcpu into read_id_reg() Tested by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx> Reviewed by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx> [1]: https://patchwork.kernel.org/patch/10880933/ Thanks, Amit Daniel > > --- > > Changes since v5: > > * Rename the visibility override flags, add some comments, and rename/ > introduce helpers to make the purpose of this code clearer. > --- > arch/arm64/kvm/sys_regs.c | 24 +++++++++++++++++++++--- > arch/arm64/kvm/sys_regs.h | 25 +++++++++++++++++++++++++ > 2 files changed, 46 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index a5d14b5..c86a7b0 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1927,6 +1927,12 @@ static void perform_access(struct kvm_vcpu *vcpu, > { > trace_kvm_sys_access(*vcpu_pc(vcpu), params, r); > > + /* Check for regs disabled by runtime config */ > + if (sysreg_hidden_from_guest(vcpu, r)) { > + kvm_inject_undefined(vcpu); > + return; > + } > + > /* > * Not having an accessor means that we have configured a trap > * that we don't know how to handle. This certainly qualifies > @@ -2438,6 +2444,10 @@ int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg > if (!r) > return get_invariant_sys_reg(reg->id, uaddr); > > + /* Check for regs disabled by runtime config */ > + if (sysreg_hidden_from_user(vcpu, r)) > + return -ENOENT; > + > if (r->get_user) > return (r->get_user)(vcpu, r, reg, uaddr); > > @@ -2459,6 +2469,10 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg > if (!r) > return set_invariant_sys_reg(reg->id, uaddr); > > + /* Check for regs disabled by runtime config */ > + if (sysreg_hidden_from_user(vcpu, r)) > + return -ENOENT; > + > if (r->set_user) > return (r->set_user)(vcpu, r, reg, uaddr); > > @@ -2515,7 +2529,8 @@ static bool copy_reg_to_user(const struct sys_reg_desc *reg, u64 __user **uind) > return true; > } > > -static int walk_one_sys_reg(const struct sys_reg_desc *rd, > +static int walk_one_sys_reg(const struct kvm_vcpu *vcpu, > + const struct sys_reg_desc *rd, > u64 __user **uind, > unsigned int *total) > { > @@ -2526,6 +2541,9 @@ static int walk_one_sys_reg(const struct sys_reg_desc *rd, > if (!(rd->reg || rd->get_user)) > return 0; > > + if (sysreg_hidden_from_user(vcpu, rd)) > + return 0; > + > if (!copy_reg_to_user(rd, uind)) > return -EFAULT; > > @@ -2554,9 +2572,9 @@ static int walk_sys_regs(struct kvm_vcpu *vcpu, u64 __user *uind) > int cmp = cmp_sys_reg(i1, i2); > /* target-specific overrides generic entry. */ > if (cmp <= 0) > - err = walk_one_sys_reg(i1, &uind, &total); > + err = walk_one_sys_reg(vcpu, i1, &uind, &total); > else > - err = walk_one_sys_reg(i2, &uind, &total); > + err = walk_one_sys_reg(vcpu, i2, &uind, &total); > > if (err) > return err; > diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h > index 3b1bc7f..2be9950 100644 > --- a/arch/arm64/kvm/sys_regs.h > +++ b/arch/arm64/kvm/sys_regs.h > @@ -64,8 +64,15 @@ struct sys_reg_desc { > const struct kvm_one_reg *reg, void __user *uaddr); > int (*set_user)(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > const struct kvm_one_reg *reg, void __user *uaddr); > + > + /* Return mask of REG_* runtime visibility overrides */ > + unsigned int (*visibility)(const struct kvm_vcpu *vcpu, > + const struct sys_reg_desc *rd); > }; > > +#define REG_HIDDEN_USER (1 << 0) /* hidden from userspace ioctls */ > +#define REG_HIDDEN_GUEST (1 << 1) /* hidden from guest */ > + > static inline void print_sys_reg_instr(const struct sys_reg_params *p) > { > /* Look, we even formatted it for you to paste into the table! */ > @@ -102,6 +109,24 @@ static inline void reset_val(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r > __vcpu_sys_reg(vcpu, r->reg) = r->val; > } > > +static inline bool sysreg_hidden_from_guest(const struct kvm_vcpu *vcpu, > + const struct sys_reg_desc *r) > +{ > + if (likely(!r->visibility)) > + return false; > + > + return r->visibility(vcpu, r) & REG_HIDDEN_GUEST; > +} > + > +static inline bool sysreg_hidden_from_user(const struct kvm_vcpu *vcpu, > + const struct sys_reg_desc *r) > +{ > + if (likely(!r->visibility)) > + return false; > + > + return r->visibility(vcpu, r) & REG_HIDDEN_USER; > +} > + > static inline int cmp_sys_reg(const struct sys_reg_desc *i1, > const struct sys_reg_desc *i2) > { > -- > 2.1.4 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
