| Message ID | 20180417183735.56985-4-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Apr 17, 2018 at 07:37:27PM +0100, Mark Rutland wrote: > In subsequent patches we're going to expose ptrauth to the host kernel > and userspace, but things are a bit trickier for guest kernels. For the > time being, let's hide ptrauth from KVM guests. > > Regardless of how well-behaved the guest kernel is, guest userspace > could attempt to use ptrauth instructions, triggering a trap to EL2, > resulting in noise from kvm_handle_unknown_ec(). So let's write up a > handler for the PAC trap, which silently injects an UNDEF into the > guest, as if the feature were really missing. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Christoffer Dall <cdall@kernel.org> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: kvmarm@lists.cs.columbia.edu > --- > arch/arm64/kvm/handle_exit.c | 18 ++++++++++++++++++ > arch/arm64/kvm/sys_regs.c | 9 +++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index e5e741bfffe1..5114ad691eae 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -173,6 +173,23 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run) > return 1; > } > > +/* > + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into > + * a NOP), or guest EL1 access to a ptrauth register. > + */ > +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) > +{ > + /* > + * We don't currently suport ptrauth in a guest, and we mask the ID > + * registers to prevent well-behaved guests from trying to make use of > + * it. > + * > + * Inject an UNDEF, as if the feature really isn't present. > + */ > + kvm_inject_undefined(vcpu); > + return 1; > +} > + > static exit_handle_fn arm_exit_handlers[] = { > [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec, > [ESR_ELx_EC_WFx] = kvm_handle_wfx, > @@ -195,6 +212,7 @@ static exit_handle_fn arm_exit_handlers[] = { > [ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug, > [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug, > [ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd, > + [ESR_ELx_EC_PAC] = kvm_handle_ptrauth, > }; > > static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu) > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 806b0b126a64..eee399c35e84 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1000,6 +1000,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) > task_pid_nr(current)); > > val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); > + } else if (id == SYS_ID_AA64ISAR1_EL1) { > + const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) | > + (0xfUL << ID_AA64ISAR1_API_SHIFT) | > + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | > + (0xfUL << ID_AA64ISAR1_GPI_SHIFT); > + if (val & ptrauth_mask) > + pr_err_once("kvm [%i]: ptrauth unsupported for guests, suppressing\n", > + task_pid_nr(current)); Marc just changed the equivalent SVE pr_err_once() to kvm_debug(). So we probably want to do the same here. > + val &= ~ptrauth_mask; > } else if (id == SYS_ID_AA64MMFR1_EL1) { > if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) > pr_err_once("kvm [%i]: LORegions unsupported for guests, suppressing\n", > -- > 2.11.0 > Otherwise Reviewed-by: Andrew Jones <drjones@redhat.com>
On Wed, Apr 18, 2018 at 03:19:26PM +0200, Andrew Jones wrote: > On Tue, Apr 17, 2018 at 07:37:27PM +0100, Mark Rutland wrote: > > @@ -1000,6 +1000,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) > > task_pid_nr(current)); > > > > val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); > > + } else if (id == SYS_ID_AA64ISAR1_EL1) { > > + const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) | > > + (0xfUL << ID_AA64ISAR1_API_SHIFT) | > > + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | > > + (0xfUL << ID_AA64ISAR1_GPI_SHIFT); > > + if (val & ptrauth_mask) > > + pr_err_once("kvm [%i]: ptrauth unsupported for guests, suppressing\n", > > + task_pid_nr(current)); > > Marc just changed the equivalent SVE pr_err_once() to kvm_debug(). > So we probably want to do the same here. Good point. Done. > > + val &= ~ptrauth_mask; > > } else if (id == SYS_ID_AA64MMFR1_EL1) { > > if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) > > pr_err_once("kvm [%i]: LORegions unsupported for guests, suppressing\n", > > -- > > 2.11.0 > > > > Otherwise > > Reviewed-by: Andrew Jones <drjones@redhat.com> Cheers! Mark.
On Tue, Apr 17, 2018 at 07:37:27PM +0100, Mark Rutland wrote: > In subsequent patches we're going to expose ptrauth to the host kernel > and userspace, but things are a bit trickier for guest kernels. For the > time being, let's hide ptrauth from KVM guests. > > Regardless of how well-behaved the guest kernel is, guest userspace > could attempt to use ptrauth instructions, triggering a trap to EL2, > resulting in noise from kvm_handle_unknown_ec(). So let's write up a > handler for the PAC trap, which silently injects an UNDEF into the > guest, as if the feature were really missing. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Christoffer Dall <cdall@kernel.org> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: kvmarm@lists.cs.columbia.edu > --- > arch/arm64/kvm/handle_exit.c | 18 ++++++++++++++++++ > arch/arm64/kvm/sys_regs.c | 9 +++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index e5e741bfffe1..5114ad691eae 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -173,6 +173,23 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run) > return 1; > } > > +/* > + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into > + * a NOP), or guest EL1 access to a ptrauth register. > + */ > +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) > +{ > + /* > + * We don't currently suport ptrauth in a guest, and we mask the ID > + * registers to prevent well-behaved guests from trying to make use of > + * it. > + * > + * Inject an UNDEF, as if the feature really isn't present. > + */ > + kvm_inject_undefined(vcpu); > + return 1; > +} > + > static exit_handle_fn arm_exit_handlers[] = { > [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec, > [ESR_ELx_EC_WFx] = kvm_handle_wfx, > @@ -195,6 +212,7 @@ static exit_handle_fn arm_exit_handlers[] = { > [ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug, > [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug, > [ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd, > + [ESR_ELx_EC_PAC] = kvm_handle_ptrauth, > }; > > static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu) > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 806b0b126a64..eee399c35e84 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1000,6 +1000,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) > task_pid_nr(current)); > > val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); > + } else if (id == SYS_ID_AA64ISAR1_EL1) { > + const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) | > + (0xfUL << ID_AA64ISAR1_API_SHIFT) | > + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | > + (0xfUL << ID_AA64ISAR1_GPI_SHIFT); > + if (val & ptrauth_mask) > + pr_err_once("kvm [%i]: ptrauth unsupported for guests, suppressing\n", > + task_pid_nr(current)); > + val &= ~ptrauth_mask; > } else if (id == SYS_ID_AA64MMFR1_EL1) { > if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) > pr_err_once("kvm [%i]: LORegions unsupported for guests, suppressing\n", > -- > 2.11.0 > With the change to the debugging print: Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index e5e741bfffe1..5114ad691eae 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -173,6 +173,23 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run) return 1; } +/* + * Guest usage of a ptrauth instruction (which the guest EL1 did not turn into + * a NOP), or guest EL1 access to a ptrauth register. + */ +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) +{ + /* + * We don't currently suport ptrauth in a guest, and we mask the ID + * registers to prevent well-behaved guests from trying to make use of + * it. + * + * Inject an UNDEF, as if the feature really isn't present. + */ + kvm_inject_undefined(vcpu); + return 1; +} + static exit_handle_fn arm_exit_handlers[] = { [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec, [ESR_ELx_EC_WFx] = kvm_handle_wfx, @@ -195,6 +212,7 @@ static exit_handle_fn arm_exit_handlers[] = { [ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug, [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug, [ESR_ELx_EC_FP_ASIMD] = handle_no_fpsimd, + [ESR_ELx_EC_PAC] = kvm_handle_ptrauth, }; static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 806b0b126a64..eee399c35e84 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1000,6 +1000,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz) task_pid_nr(current)); val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); + } else if (id == SYS_ID_AA64ISAR1_EL1) { + const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) | + (0xfUL << ID_AA64ISAR1_API_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPA_SHIFT) | + (0xfUL << ID_AA64ISAR1_GPI_SHIFT); + if (val & ptrauth_mask) + pr_err_once("kvm [%i]: ptrauth unsupported for guests, suppressing\n", + task_pid_nr(current)); + val &= ~ptrauth_mask; } else if (id == SYS_ID_AA64MMFR1_EL1) { if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) pr_err_once("kvm [%i]: LORegions unsupported for guests, suppressing\n",
In subsequent patches we're going to expose ptrauth to the host kernel and userspace, but things are a bit trickier for guest kernels. For the time being, let's hide ptrauth from KVM guests. Regardless of how well-behaved the guest kernel is, guest userspace could attempt to use ptrauth instructions, triggering a trap to EL2, resulting in noise from kvm_handle_unknown_ec(). So let's write up a handler for the PAC trap, which silently injects an UNDEF into the guest, as if the feature were really missing. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Christoffer Dall <cdall@kernel.org> Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: kvmarm@lists.cs.columbia.edu --- arch/arm64/kvm/handle_exit.c | 18 ++++++++++++++++++ arch/arm64/kvm/sys_regs.c | 9 +++++++++ 2 files changed, 27 insertions(+)