KVM: arm64: Workaround Cortex-A510's single-step and PAC trap errata

Cortex-A510's erratum #2077057 causes SPSR_EL2 to be corrupted when
single-stepping authenticated ERET instructions. A single step is
expected, but a pointer authentication trap is taken instead. The
erratum causes SPSR_EL1 to be copied to SPSR_EL2, which could allow
EL1 to cause a return to EL2 with a guest controlled ELR_EL2.

Because the conditions require an ERET into active-not-pending state,
this is only a problem for the EL2 when EL2 is stepping EL1. In this case
the previous SPSR_EL2 value is preserved in struct kvm_vcpu, and can be
restored.

Cc: stable@vger.kernel.org # 53960faf: arm64: Add Cortex-A510 CPU part definition
Cc: stable@vger.kernel.org
Signed-off-by: James Morse <james.morse@arm.com>
[maz: fixup cpucaps ordering]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220127122052.1584324-5-james.morse@arm.com

Documentation/arm64/silicon-errata.rst

@@ -100,6 +100,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A510     | #2051678        | ARM64_ERRATUM_2051678       |
 +----------------+-----------------+-----------------+-----------------------------+
+| ARM            | Cortex-A510     | #2077057        | ARM64_ERRATUM_2077057       |
++----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A710     | #2119858        | ARM64_ERRATUM_2119858       |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A710     | #2054223        | ARM64_ERRATUM_2054223       |

arch/arm64/Kconfig

@@ -680,6 +680,22 @@ config ARM64_ERRATUM_2051678
 
 	  If unsure, say Y.
 
+config ARM64_ERRATUM_2077057
+	bool "Cortex-A510: 2077057: workaround software-step corrupting SPSR_EL2"
+	help
+	  This option adds the workaround for ARM Cortex-A510 erratum 2077057.
+	  Affected Cortex-A510 may corrupt SPSR_EL2 when the a step exception is
+	  expected, but a Pointer Authentication trap is taken instead. The
+	  erratum causes SPSR_EL1 to be copied to SPSR_EL2, which could allow
+	  EL1 to cause a return to EL2 with a guest controlled ELR_EL2.
+
+	  This can only happen when EL2 is stepping EL1.
+
+	  When these conditions occur, the SPSR_EL2 value is unchanged from the
+	  previous guest entry, and can be restored from the in-memory copy.
+
+	  If unsure, say Y.
+
 config ARM64_ERRATUM_2119858
 	bool "Cortex-A710/X2: 2119858: workaround TRBE overwriting trace data in FILL mode"
 	default y

arch/arm64/kernel/cpu_errata.c

@@ -600,6 +600,14 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
 	},
 #endif
+#ifdef CONFIG_ARM64_ERRATUM_2077057
+	{
+		.desc = "ARM erratum 2077057",
+		.capability = ARM64_WORKAROUND_2077057,
+		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
+		ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2),
+	},
+#endif
 #ifdef CONFIG_ARM64_ERRATUM_2064142
 	{
 		.desc = "ARM erratum 2064142",

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -402,6 +402,24 @@ static inline bool kvm_hyp_handle_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 	return false;
 }
 
+static inline void synchronize_vcpu_pstate(struct kvm_vcpu *vcpu, u64 *exit_code)
+{
+	/*
+	 * Check for the conditions of Cortex-A510's #2077057. When these occur
+	 * SPSR_EL2 can't be trusted, but isn't needed either as it is
+	 * unchanged from the value in vcpu_gp_regs(vcpu)->pstate.
+	 * Are we single-stepping the guest, and took a PAC exception from the
+	 * active-not-pending state?
+	 */
+	if (cpus_have_final_cap(ARM64_WORKAROUND_2077057)		&&
+	    vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP			&&
+	    *vcpu_cpsr(vcpu) & DBG_SPSR_SS				&&
+	    ESR_ELx_EC(read_sysreg_el2(SYS_ESR)) == ESR_ELx_EC_PAC)
+		write_sysreg_el2(*vcpu_cpsr(vcpu), SYS_SPSR);
+
+	vcpu->arch.ctxt.regs.pstate = read_sysreg_el2(SYS_SPSR);
+}
+
 /*
  * Return true when we were able to fixup the guest exit and should return to
  * the guest, false when we should restore the host state and return to the
@@ -413,7 +431,7 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 	 * Save PSTATE early so that we can evaluate the vcpu mode
 	 * early on.
 	 */
-	vcpu->arch.ctxt.regs.pstate = read_sysreg_el2(SYS_SPSR);
+	synchronize_vcpu_pstate(vcpu, exit_code);
 
 	/*
 	 * Check whether we want to repaint the state one way or

arch/arm64/tools/cpucaps

@@ -55,9 +55,10 @@ WORKAROUND_1418040
 WORKAROUND_1463225
 WORKAROUND_1508412
 WORKAROUND_1542419
-WORKAROUND_2064142
-WORKAROUND_2038923
 WORKAROUND_1902691
+WORKAROUND_2038923
+WORKAROUND_2064142
+WORKAROUND_2077057
 WORKAROUND_TRBE_OVERWRITE_FILL_MODE
 WORKAROUND_TSB_FLUSH_FAILURE
 WORKAROUND_TRBE_WRITE_OUT_OF_RANGE