From: Mark Rutland mark.rutland@arm.com
mainline inclusion from v4.20-rc3 commit a1ee8abb95c5 category: feature bugzilla: 27615 CVE: NA
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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.
Reviewed-by: Richard Henderson richard.henderson@linaro.org Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Kristina Martsenko kristina.martsenko@arm.com Reviewed-by: Andrew Jones drjones@redhat.com Reviewed-by: Christoffer Dall christoffer.dall@arm.com Cc: Marc Zyngier marc.zyngier@arm.com Cc: kvmarm@lists.cs.columbia.edu Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Reviewed-by: Hanjun Guo guohanjun@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- arch/arm64/kvm/handle_exit.c | 18 ++++++++++++++++++ arch/arm64/kvm/sys_regs.c | 8 ++++++++ 2 files changed, 26 insertions(+)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index f5feef3c1e885..338efbcec03ae 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -178,6 +178,23 @@ 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). + */ +static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu, struct kvm_run *run) +{ + /* + * We don't currently support 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, @@ -200,6 +217,7 @@ 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 29496548c56b9..277056d181955 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1077,6 +1077,14 @@ static u64 read_id_reg(struct kvm_vcpu *vcpu, kvm_debug("SVE unsupported for guests, suppressing\n");
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) + kvm_debug("ptrauth unsupported for guests, suppressing\n"); + val &= ~ptrauth_mask; } else if (id == SYS_ID_AA64MMFR1_EL1) { if (val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT)) kvm_debug("LORegions unsupported for guests, suppressing\n");