From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: arnd@arndb.de, catalin.marinas@arm.com, cdall@kernel.org,
drjones@redhat.com, kvmarm@lists.cs.columbia.edu,
linux-arch@vger.kernel.org, marc.zyngier@arm.com,
mark.rutland@arm.com, ramana.radhakrishnan@arm.com,
suzuki.poulose@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, awallis@codeaurora.org,
kernel-hardening@lists.openwall.com
Subject: [PATCHv3 03/11] arm64/kvm: hide ptrauth from guests
Date: Tue, 17 Apr 2018 19:37:27 +0100 [thread overview]
Message-ID: <20180417183735.56985-4-mark.rutland@arm.com> (raw)
In-Reply-To: <20180417183735.56985-1-mark.rutland@arm.com>
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
next prev parent reply other threads:[~2018-04-17 18:37 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-17 18:37 [PATCHv3 00/11] ARMv8.3 pointer authentication userspace support Mark Rutland
2018-04-17 18:37 ` [PATCHv3 01/11] arm64: add pointer authentication register bits Mark Rutland
2018-04-17 18:37 ` [PATCHv3 02/11] arm64/kvm: consistently handle host HCR_EL2 flags Mark Rutland
2018-04-27 9:51 ` Christoffer Dall
2018-04-27 10:13 ` Mark Rutland
2018-04-17 18:37 ` Mark Rutland [this message]
2018-04-18 13:19 ` [PATCHv3 03/11] arm64/kvm: hide ptrauth from guests Andrew Jones
2018-04-18 13:47 ` Mark Rutland
2018-04-27 9:51 ` Christoffer Dall
2018-04-17 18:37 ` [PATCHv3 04/11] arm64: Don't trap host pointer auth use to EL2 Mark Rutland
2018-04-27 9:52 ` Christoffer Dall
2018-04-17 18:37 ` [PATCHv3 05/11] arm64/cpufeature: detect pointer authentication Mark Rutland
2018-04-17 18:37 ` [PATCHv3 06/11] asm-generic: mm_hooks: allow hooks to be overridden individually Mark Rutland
2018-04-17 19:56 ` Arnd Bergmann
2018-04-18 11:38 ` Mark Rutland
2018-04-17 18:37 ` [PATCHv3 07/11] arm64: add basic pointer authentication support Mark Rutland
2018-04-25 11:23 ` Catalin Marinas
2018-04-27 10:27 ` Mark Rutland
2018-04-17 18:37 ` [PATCHv3 08/11] arm64: expose user PAC bit positions via ptrace Mark Rutland
2018-04-17 18:37 ` [PATCHv3 09/11] arm64: perf: strip PAC when unwinding userspace Mark Rutland
2018-04-17 18:37 ` [PATCHv3 10/11] arm64: enable pointer authentication Mark Rutland
2018-04-17 18:37 ` [PATCHv3 11/11] arm64: docs: document " Mark Rutland
2018-04-22 8:05 ` Pavel Machek
2018-04-22 8:47 ` Marc Zyngier
2018-04-22 9:00 ` Pavel Machek
2018-04-25 12:27 ` Catalin Marinas
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