Re: [PATCH 1/6] kvm: arm64: Prevent use of invalid PSCI v0.1 function IDs

On Tue, Dec 08, 2020 at 03:56:39PM +0000, Marc Zyngier wrote:

On 2020-12-08 14:24, David Brazdil wrote:

quoted

PSCI driver exposes a struct containing the PSCI v0.1 function IDs
configured in the DT. However, the struct does not convey the
information whether these were set from DT or contain the default value
zero. This could be a problem for PSCI proxy in KVM protected mode.

Extend config passed to KVM with a bit mask with individual bits set
depending on whether the corresponding function pointer in psci_ops is
set, eg. set bit for PSCI_CPU_SUSPEND if psci_ops.cpu_suspend != NULL.

Previously config was split into multiple global variables. Put
everything into a single struct for convenience.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: David Brazdil <redacted>
---
 arch/arm64/include/asm/kvm_host.h    | 20 +++++++++++
 arch/arm64/kvm/arm.c                 | 14 +++++---
 arch/arm64/kvm/hyp/nvhe/psci-relay.c | 53 +++++++++++++++++++++-------
 3 files changed, 70 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h

b/arch/arm64/include/asm/kvm_host.h
index 11beda85ee7e..828d50d40dc2 100644

--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h

@@ -17,6 +17,7 @@
 #include <linux/jump_label.h>
 #include <linux/kvm_types.h>
 #include <linux/percpu.h>
+#include <linux/psci.h>
 #include <asm/arch_gicv3.h>
 #include <asm/barrier.h>
 #include <asm/cpufeature.h>

@@ -240,6 +241,25 @@ struct kvm_host_data {
 	struct kvm_pmu_events pmu_events;
 };

+#define KVM_HOST_PSCI_0_1_CPU_SUSPEND	BIT(0)
+#define KVM_HOST_PSCI_0_1_CPU_ON	BIT(1)
+#define KVM_HOST_PSCI_0_1_CPU_OFF	BIT(2)
+#define KVM_HOST_PSCI_0_1_MIGRATE	BIT(3)
+
+struct kvm_host_psci_config {
+	/* PSCI version used by host. */
+	u32 version;
+
+	/* Function IDs used by host if version is v0.1. */
+	struct psci_0_1_function_ids function_ids_0_1;
+
+	/* Bitmask of functions enabled for v0.1, bits KVM_HOST_PSCI_0_1_*. */
+	unsigned int enabled_functions_0_1;

Nit: the conventional type for bitmaps is 'unsigned long'.
Also, "enabled" seems odd. Isn't it actually "available"?

Sure, that or "implemented" works here.

Since there are only 4 functions here, it might make sense to use
independent bools rather than a bitmap, which might make this a bit
simpler...

quoted

get_psci_0_1_function_ids();
+	kvm_host_psci_config.version = psci_ops.get_version();
+
+	if (kvm_host_psci_config.version == PSCI_VERSION(0, 1)) {
+		kvm_host_psci_config.function_ids_0_1 = get_psci_0_1_function_ids();
+		kvm_host_psci_config.enabled_functions_0_1 =
+			(psci_ops.cpu_suspend ? KVM_HOST_PSCI_0_1_CPU_SUSPEND : 0) |
+			(psci_ops.cpu_off ? KVM_HOST_PSCI_0_1_CPU_OFF : 0) |
+			(psci_ops.cpu_on ? KVM_HOST_PSCI_0_1_CPU_ON : 0) |
+			(psci_ops.migrate ? KVM_HOST_PSCI_0_1_MIGRATE : 0);

... since e.g. this could be roughly:

	kvm_host_psci_config.cpu_suspend_implemented = psci_ops.cpu_suspend;
	kvm_host_psci_config.cpu_off_implemented = psci_ops.cpu_off;
	kvm_host_psci_config.cpu_on_implemented = psci_ops.cpu_on;
	kvm_host_psci_config.migrate_implemented = psci_ops.migrate;

quoted

+static inline bool is_psci_0_1_cpu_suspend(u64 func_id)
+{
+	return is_psci_0_1_function_enabled(KVM_HOST_PSCI_0_1_CPU_SUSPEND) &&
+	       (func_id == kvm_host_psci_config.function_ids_0_1.cpu_suspend);
+}

...and similarly:

	return  kvm_host_psci_config.cpu_suspend_implemented &&
		func_id == kvm_host_psci_config.function_ids_0_1.cpu_suspend)

Otherwise looks OK. Don't bother respinning the series for my
comments, I can tidy things up as I apply it if there are no other
issues.

FWIW, I'm happy with whatever choose to do here, so don't feel like you
have to follow my suggestions above.

Thanks,
Mark.

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