[PATCH v4 0/5] ARM: arm64: Add SMCCC TRNG entropy service

[PATCH v4 0/5] ARM: arm64: Add SMCCC TRNG entropy service

[Andre Przywara]

Hi,

a small update to v3, fixing the rare build issue the kernel test robot
pointed out, and changing the priority of the SMCCC vs. RNDR call in
the arm64 patch, as per discussion with Ard.
Adding tags on the way. Changelog below.

Cheers,
Andre
==============================

The ARM architected TRNG firmware interface, described in ARM spec
DEN0098[1], defines an ARM SMCCC based interface to a true random number
generator, provided by firmware.

This series collects all the patches implementing this in various
places: as a user feeding into the ARCH_RANDOM pool, both for ARM and
arm64, and as a service provider for KVM guests.

Patch 1 introduces the interface definition used by all three entities.
Patch 2 prepares the Arm SMCCC firmware driver to probe for the
interface. This patch is needed to avoid a later dependency on *two*
patches (there might be a better solution to this problem).

Patch 3 implements the ARM part, patch 4 is the arm64 version.
The final patch 5 adds support to provide random numbers to KVM guests.

This was tested on:
- QEMU -kernel (no SMCCC, regression test)
- Juno w/ prototype of the h/w Trusted RNG support
- mainline KVM (SMCCC, but no TRNG: regression test)
- ARM and arm64 KVM guests, using the KVM service in patch 5/5

Based on arm64/for-next/core, please let me know if I should rebased on
something else. A git repo is accessible at:
https://gitlab.arm.com/linux-arm/linux-ap/-/commits/smccc-trng/v4/

Cheers,
Andre

[1] https://developer.arm.com/documentation/den0098/latest/

Changelog v3 ... v4:
- include cache.h to always have __ro_after_init defined
- change order of SMCCC call vs. RNDR call in arm64's archrandom.h
- adding LinusW's R-b: tags

Changelog v2 ... v3:
- ARM: fix compilation with randconfig
- arm64: use SMCCC call also in arch_get_random_seed_long_early()
- KVM: comment on return value usage
- KVM: use more interesting UUID (enjoy, Marc!)
- KVM: use bitmaps instead of open coded long arrays
- KVM: drop direct usage of arch_get_random() interface

Changelog "v1" ... v2:
- trigger ARCH_RANDOM initialisation from the SMCCC firmware driver
- use a single bool in smccc.c to hold the initialisation state for arm64
- handle endianess correctly in the KVM provider

Andre Przywara (2):
  firmware: smccc: Introduce SMCCC TRNG framework
  arm64: Add support for SMCCC TRNG entropy source

Ard Biesheuvel (3):
  firmware: smccc: Add SMCCC TRNG function call IDs
  ARM: implement support for SMCCC TRNG entropy source
  KVM: arm64: implement the TRNG hypervisor call

 arch/arm/Kconfig                    |  4 ++
 arch/arm/include/asm/archrandom.h   | 74 +++++++++++++++++++++++++
 arch/arm64/include/asm/archrandom.h | 82 ++++++++++++++++++++++++----
 arch/arm64/include/asm/kvm_host.h   |  2 +
 arch/arm64/kvm/Makefile             |  2 +-
 arch/arm64/kvm/hypercalls.c         |  6 ++
 arch/arm64/kvm/trng.c               | 85 +++++++++++++++++++++++++++++
 drivers/firmware/smccc/smccc.c      |  6 ++
 include/linux/arm-smccc.h           | 31 +++++++++++
 9 files changed, 281 insertions(+), 11 deletions(-)
 create mode 100644 arch/arm/include/asm/archrandom.h
 create mode 100644 arch/arm64/kvm/trng.c

-- 
2.17.1

[PATCH v4 1/5] firmware: smccc: Add SMCCC TRNG function call IDs

[Andre Przywara]

From: Ard Biesheuvel <ardb@kernel.org>

The ARM architected TRNG firmware interface, described in ARM spec
DEN0098, define an ARM SMCCC based interface to a true random number
generator, provided by firmware.

Add the definitions of the SMCCC functions as defined by the spec.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
 include/linux/arm-smccc.h | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index f860645f6512..62c54234576c 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -102,6 +102,37 @@
 			   ARM_SMCCC_OWNER_STANDARD_HYP,	\
 			   0x21)
 
+/* TRNG entropy source calls (defined by ARM DEN0098) */
+#define ARM_SMCCC_TRNG_VERSION					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x50)
+
+#define ARM_SMCCC_TRNG_FEATURES					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x51)
+
+#define ARM_SMCCC_TRNG_GET_UUID					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x52)
+
+#define ARM_SMCCC_TRNG_RND32					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x53)
+
+#define ARM_SMCCC_TRNG_RND64					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_64,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x53)
+
 /*
  * Return codes defined in ARM DEN 0070A
  * ARM DEN 0070A is now merged/consolidated into ARM DEN 0028 C
-- 
2.17.1

Re: [PATCH v4 1/5] firmware: smccc: Add SMCCC TRNG function call IDs

[Sudeep Holla]

On Fri, Dec 11, 2020 at 04:00:01PM +0000, Andre Przywara wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> The ARM architected TRNG firmware interface, described in ARM spec
> DEN0098, define an ARM SMCCC based interface to a true random number
> generator, provided by firmware.
> 
> Add the definitions of the SMCCC functions as defined by the spec.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep

[PATCH v4 2/5] firmware: smccc: Introduce SMCCC TRNG framework

[Andre Przywara]

The ARM DEN0098 document describe an SMCCC based firmware service to
deliver hardware generated random numbers. Its existence is advertised
according to the SMCCC v1.1 specification.

Add a (dummy) call to probe functions implemented in each architecture
(ARM and arm64), to determine the existence of this interface.
For now this return false, but this will be overwritten by each
architecture's support patch.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
 arch/arm/include/asm/archrandom.h   | 10 ++++++++++
 arch/arm64/include/asm/archrandom.h | 12 ++++++++++++
 drivers/firmware/smccc/smccc.c      |  6 ++++++
 3 files changed, 28 insertions(+)
 create mode 100644 arch/arm/include/asm/archrandom.h

diff --git a/arch/arm/include/asm/archrandom.h b/arch/arm/include/asm/archrandom.h
new file mode 100644
index 000000000000..a8e84ca5c2ee
--- /dev/null
+++ b/arch/arm/include/asm/archrandom.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARCHRANDOM_H
+#define _ASM_ARCHRANDOM_H
+
+static inline bool __init smccc_probe_trng(void)
+{
+	return false;
+}
+
+#endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
index ffb1a40d5475..abe07c21da8e 100644
--- a/arch/arm64/include/asm/archrandom.h
+++ b/arch/arm64/include/asm/archrandom.h
@@ -8,6 +8,11 @@
 #include <linux/kernel.h>
 #include <asm/cpufeature.h>
 
+static inline bool __init smccc_probe_trng(void)
+{
+	return false;
+}
+
 static inline bool __arm64_rndr(unsigned long *v)
 {
 	bool ok;
@@ -79,5 +84,12 @@ arch_get_random_seed_long_early(unsigned long *v)
 }
 #define arch_get_random_seed_long_early arch_get_random_seed_long_early
 
+#else /* !CONFIG_ARCH_RANDOM */
+
+static inline bool __init smccc_probe_trng(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_ARCH_RANDOM */
 #endif /* _ASM_ARCHRANDOM_H */
diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
index 00c88b809c0c..d52bfc5ed5e4 100644
--- a/drivers/firmware/smccc/smccc.c
+++ b/drivers/firmware/smccc/smccc.c
@@ -5,16 +5,22 @@
 
 #define pr_fmt(fmt) "smccc: " fmt
 
+#include <linux/cache.h>
 #include <linux/init.h>
 #include <linux/arm-smccc.h>
+#include <asm/archrandom.h>
 
 static u32 smccc_version = ARM_SMCCC_VERSION_1_0;
 static enum arm_smccc_conduit smccc_conduit = SMCCC_CONDUIT_NONE;
 
+bool __ro_after_init smccc_trng_available = false;
+
 void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit)
 {
 	smccc_version = version;
 	smccc_conduit = conduit;
+
+	smccc_trng_available = smccc_probe_trng();
 }
 
 enum arm_smccc_conduit arm_smccc_1_1_get_conduit(void)
-- 
2.17.1

Re: [PATCH v4 2/5] firmware: smccc: Introduce SMCCC TRNG framework

[Sudeep Holla]

On Fri, Dec 11, 2020 at 04:00:02PM +0000, Andre Przywara wrote:
> The ARM DEN0098 document describe an SMCCC based firmware service to
> deliver hardware generated random numbers. Its existence is advertised
> according to the SMCCC v1.1 specification.
> 
> Add a (dummy) call to probe functions implemented in each architecture
> (ARM and arm64), to determine the existence of this interface.
> For now this return false, but this will be overwritten by each
> architecture's support patch.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep

[PATCH v4 3/5] ARM: implement support for SMCCC TRNG entropy source

[Andre Przywara]

From: Ard Biesheuvel <ardb@kernel.org>

Implement arch_get_random_seed_*() for ARM based on the firmware
or hypervisor provided entropy source described in ARM DEN0098.

This will make the kernel's random number generator consume entropy
provided by this interface, at early boot, and periodically at
runtime when reseeding.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[Andre: rework to be initialised by the SMCCC firmware driver]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
 arch/arm/Kconfig                  |  4 ++
 arch/arm/include/asm/archrandom.h | 64 +++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fe2f17eb2b50..a6d2d66f4110 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1667,6 +1667,10 @@ config STACKPROTECTOR_PER_TASK
 	  Enable this option to switch to a different method that uses a
 	  different canary value for each task.
 
+config ARCH_RANDOM
+	def_bool y
+	depends on HAVE_ARM_SMCCC_DISCOVERY
+
 endmenu
 
 menu "Boot options"
diff --git a/arch/arm/include/asm/archrandom.h b/arch/arm/include/asm/archrandom.h
index a8e84ca5c2ee..f3e96a5b65f8 100644
--- a/arch/arm/include/asm/archrandom.h
+++ b/arch/arm/include/asm/archrandom.h
@@ -2,9 +2,73 @@
 #ifndef _ASM_ARCHRANDOM_H
 #define _ASM_ARCHRANDOM_H
 
+#ifdef CONFIG_ARCH_RANDOM
+
+#include <linux/arm-smccc.h>
+#include <linux/kernel.h>
+
+#define ARM_SMCCC_TRNG_MIN_VERSION     0x10000UL
+
+extern bool smccc_trng_available;
+
+static inline bool __init smccc_probe_trng(void)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res);
+	if ((s32)res.a0 < 0)
+		return false;
+	if (res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION) {
+		/* double check that the 32-bit flavor is available */
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_FEATURES,
+				     ARM_SMCCC_TRNG_RND32,
+				     &res);
+		if ((s32)res.a0 >= 0)
+			return true;
+	}
+
+	return false;
+}
+
+static inline bool __must_check arch_get_random_long(unsigned long *v)
+{
+	return false;
+}
+
+static inline bool __must_check arch_get_random_int(unsigned int *v)
+{
+	return false;
+}
+
+static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
+{
+	struct arm_smccc_res res;
+
+	if (smccc_trng_available) {
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND32, 8 * sizeof(*v), &res);
+
+		if (res.a0 != 0)
+			return false;
+
+		*v = res.a3;
+		return true;
+	}
+
+	return false;
+}
+
+static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+{
+	return arch_get_random_seed_long((unsigned long *)v);
+}
+
+
+#else /* !CONFIG_ARCH_RANDOM */
+
 static inline bool __init smccc_probe_trng(void)
 {
 	return false;
 }
 
+#endif /* CONFIG_ARCH_RANDOM */
 #endif /* _ASM_ARCHRANDOM_H */
-- 
2.17.1

[PATCH v4 4/5] arm64: Add support for SMCCC TRNG entropy source

[Andre Przywara]

The ARM architected TRNG firmware interface, described in ARM spec
DEN0098, defines an ARM SMCCC based interface to a true random number
generator, provided by firmware.
This can be discovered via the SMCCC >=v1.1 interface, and provides
up to 192 bits of entropy per call.

Hook this SMC call into arm64's arch_get_random_*() implementation,
coming to the rescue when the CPU does not implement the ARM v8.5 RNG
system registers.

For the detection, we piggy back on the PSCI/SMCCC discovery (which gives
us the conduit to use (hvc/smc)), then try to call the
ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is
not implemented.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 arch/arm64/include/asm/archrandom.h | 72 ++++++++++++++++++++++++-----
 1 file changed, 61 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
index abe07c21da8e..e188228b2bcc 100644
--- a/arch/arm64/include/asm/archrandom.h
+++ b/arch/arm64/include/asm/archrandom.h
@@ -4,13 +4,24 @@
 
 #ifdef CONFIG_ARCH_RANDOM
 
+#include <linux/arm-smccc.h>
 #include <linux/bug.h>
 #include <linux/kernel.h>
 #include <asm/cpufeature.h>
 
+#define ARM_SMCCC_TRNG_MIN_VERSION	0x10000UL
+
+extern bool smccc_trng_available;
+
 static inline bool __init smccc_probe_trng(void)
 {
-	return false;
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res);
+	if ((s32)res.a0 < 0)
+		return false;
+
+	return res.a0 >= ARM_SMCCC_TRNG_MIN_VERSION;
 }
 
 static inline bool __arm64_rndr(unsigned long *v)
@@ -43,26 +54,55 @@ static inline bool __must_check arch_get_random_int(unsigned int *v)
 
 static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
 {
+	struct arm_smccc_res res;
+
+	/*
+	 * We prefer the SMCCC call, since its semantics (return actual
+	 * hardware backed entropy) is closer to the idea behind this
+	 * function here than what even the RNDRSS register provides
+	 * (the output of a pseudo RNG freshly seeded by a TRNG).
+	 */
+	if (smccc_trng_available) {
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
+		if ((int)res.a0 >= 0) {
+			*v = res.a3;
+			return true;
+		}
+	}
+
 	/*
 	 * Only support the generic interface after we have detected
 	 * the system wide capability, avoiding complexity with the
 	 * cpufeature code and with potential scheduling between CPUs
 	 * with and without the feature.
 	 */
-	if (!cpus_have_const_cap(ARM64_HAS_RNG))
-		return false;
+	if (cpus_have_const_cap(ARM64_HAS_RNG))
+		return __arm64_rndr(v);
 
-	return __arm64_rndr(v);
+	return false;
 }
 
-
 static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
 {
+	struct arm_smccc_res res;
 	unsigned long val;
-	bool ok = arch_get_random_seed_long(&val);
 
-	*v = val;
-	return ok;
+	if (smccc_trng_available) {
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 32, &res);
+		if ((int)res.a0 >= 0) {
+			*v = res.a3 & GENMASK(31, 0);
+			return true;
+		}
+	}
+
+	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
+		if (__arm64_rndr(&val)) {
+			*v = val;
+			return true;
+		}
+	}
+
+	return false;
 }
 
 static inline bool __init __early_cpu_has_rndr(void)
@@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long *v)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
 
-	if (!__early_cpu_has_rndr())
-		return false;
+	if (__early_cpu_has_rndr())
+		return __arm64_rndr(v);
+
+	if (smccc_trng_available) {
+		struct arm_smccc_res res;
 
-	return __arm64_rndr(v);
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
+		if ((int)res.a0 >= 0) {
+			*v = res.a3;
+			return true;
+		}
+	}
+
+	return false;
 }
 #define arch_get_random_seed_long_early arch_get_random_seed_long_early
 
-- 
2.17.1

Re: [PATCH v4 4/5] arm64: Add support for SMCCC TRNG entropy source

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 1174 bytes --]

On Fri, Dec 11, 2020 at 04:00:04PM +0000, Andre Przywara wrote:

>  static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
>  {
> +	struct arm_smccc_res res;
> +
> +	/*
> +	 * We prefer the SMCCC call, since its semantics (return actual
> +	 * hardware backed entropy) is closer to the idea behind this
> +	 * function here than what even the RNDRSS register provides
> +	 * (the output of a pseudo RNG freshly seeded by a TRNG).
> +	 */

This logic...

> @@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long *v)
>  {
>  	WARN_ON(system_state != SYSTEM_BOOTING);
>  
> -	if (!__early_cpu_has_rndr())
> -		return false;
> +	if (__early_cpu_has_rndr())
> +		return __arm64_rndr(v);
> +
> +	if (smccc_trng_available) {
> +		struct arm_smccc_res res;
>  
> -	return __arm64_rndr(v);
> +		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
> +		if ((int)res.a0 >= 0) {
> +			*v = res.a3;
> +			return true;
> +		}
> +	}
> +
> +	return false;

...seems to also apply here but we prefer the RNDR instead of the SMCC.
We probably want to either do the same thing or add a comment saying
what's going on.

[-- Attachment #2: signature.asc --]
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Re: [PATCH v4 4/5] arm64: Add support for SMCCC TRNG entropy source

[Andre Przywara]

On Fri, 11 Dec 2020 16:26:12 +0000
Mark Brown <broonie@kernel.org> wrote:

> On Fri, Dec 11, 2020 at 04:00:04PM +0000, Andre Przywara wrote:
> 
> >  static inline bool __must_check arch_get_random_seed_long(unsigned
> > long *v) {
> > +	struct arm_smccc_res res;
> > +
> > +	/*
> > +	 * We prefer the SMCCC call, since its semantics (return
> > actual
> > +	 * hardware backed entropy) is closer to the idea behind
> > this
> > +	 * function here than what even the RNDRSS register
> > provides
> > +	 * (the output of a pseudo RNG freshly seeded by a TRNG).
> > +	 */  
> 
> This logic...
> 
> > @@ -77,10 +117,20 @@ arch_get_random_seed_long_early(unsigned long
> > *v) {
> >  	WARN_ON(system_state != SYSTEM_BOOTING);
> >  
> > -	if (!__early_cpu_has_rndr())
> > -		return false;
> > +	if (__early_cpu_has_rndr())
> > +		return __arm64_rndr(v);
> > +
> > +	if (smccc_trng_available) {
> > +		struct arm_smccc_res res;
> >  
> > -	return __arm64_rndr(v);
> > +		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64,
> > &res);
> > +		if ((int)res.a0 >= 0) {
> > +			*v = res.a3;
> > +			return true;
> > +		}
> > +	}
> > +
> > +	return false;  
> 
> ...seems to also apply here but we prefer the RNDR instead of the
> SMCC. We probably want to either do the same thing or add a comment
> saying what's going on.

Argh, you are right, I missed to change this part as well.

Will send a fixed and rebased v5 ASAP.

Cheers,
Andre

[PATCH v4 5/5] KVM: arm64: implement the TRNG hypervisor call

[Andre Przywara]

From: Ard Biesheuvel <ardb@kernel.org>

Provide a hypervisor implementation of the ARM architected TRNG firmware
interface described in ARM spec DEN0098. All function IDs are implemented,
including both 32-bit and 64-bit versions of the TRNG_RND service, which
is the centerpiece of the API.

The API is backed by the kernel's entropy pool only, to avoid guests
draining more precious direct entropy sources.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[Andre: minor fixes, drop arch_get_random() usage]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 arch/arm64/include/asm/kvm_host.h |  2 +
 arch/arm64/kvm/Makefile           |  2 +-
 arch/arm64/kvm/hypercalls.c       |  6 +++
 arch/arm64/kvm/trng.c             | 85 +++++++++++++++++++++++++++++++
 4 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/kvm/trng.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 781d029b8aa8..615932bacf76 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -652,4 +652,6 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
 #define kvm_arm_vcpu_sve_finalized(vcpu) \
 	((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
 
+int kvm_trng_call(struct kvm_vcpu *vcpu);
+
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 1504c81fbf5d..a510037e3270 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -16,7 +16,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
 	 inject_fault.o regmap.o va_layout.o handle_exit.o \
 	 guest.o debug.o reset.o sys_regs.o \
 	 vgic-sys-reg-v3.o fpsimd.o pmu.o \
-	 aarch32.o arch_timer.o \
+	 aarch32.o arch_timer.o trng.o \
 	 vgic/vgic.o vgic/vgic-init.o \
 	 vgic/vgic-irqfd.o vgic/vgic-v2.o \
 	 vgic/vgic-v3.o vgic/vgic-v4.o \
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 25ea4ecb6449..ead21b98b620 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -71,6 +71,12 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		if (gpa != GPA_INVALID)
 			val = gpa;
 		break;
+	case ARM_SMCCC_TRNG_VERSION:
+	case ARM_SMCCC_TRNG_FEATURES:
+	case ARM_SMCCC_TRNG_GET_UUID:
+	case ARM_SMCCC_TRNG_RND32:
+	case ARM_SMCCC_TRNG_RND64:
+		return kvm_trng_call(vcpu);
 	default:
 		return kvm_psci_call(vcpu);
 	}
diff --git a/arch/arm64/kvm/trng.c b/arch/arm64/kvm/trng.c
new file mode 100644
index 000000000000..99bdd7103c9c
--- /dev/null
+++ b/arch/arm64/kvm/trng.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 Arm Ltd.
+
+#include <linux/arm-smccc.h>
+#include <linux/kvm_host.h>
+
+#include <asm/kvm_emulate.h>
+
+#include <kvm/arm_hypercalls.h>
+
+#define ARM_SMCCC_TRNG_VERSION_1_0	0x10000UL
+
+/* Those values are deliberately separate from the generic SMCCC definitions. */
+#define TRNG_SUCCESS			0UL
+#define TRNG_NOT_SUPPORTED		((unsigned long)-1)
+#define TRNG_INVALID_PARAMETER		((unsigned long)-2)
+#define TRNG_NO_ENTROPY			((unsigned long)-3)
+
+#define TRNG_MAX_BITS64			192
+
+static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
+	0x0d21e000, 0x4384, 0x11eb, 0x80, 0x70, 0x52, 0x44, 0x55, 0x4e, 0x5a, 0x4c);
+
+static int kvm_trng_do_rnd(struct kvm_vcpu *vcpu, int size)
+{
+	DECLARE_BITMAP(bits, TRNG_MAX_BITS64);
+	u32 num_bits = smccc_get_arg1(vcpu);
+	int i;
+
+	if (num_bits > 3 * size) {
+		smccc_set_retval(vcpu, TRNG_INVALID_PARAMETER, 0, 0, 0);
+		return 1;
+	}
+
+	/* get as many bits as we need to fulfil the request */
+	for (i = 0; i < DIV_ROUND_UP(num_bits, BITS_PER_LONG); i++)
+		bits[i] = get_random_long();
+
+	bitmap_clear(bits, num_bits, TRNG_MAX_BITS64 - num_bits);
+
+	if (size == 32)
+		smccc_set_retval(vcpu, TRNG_SUCCESS, lower_32_bits(bits[1]),
+				 upper_32_bits(bits[0]), lower_32_bits(bits[0]));
+	else
+		smccc_set_retval(vcpu, TRNG_SUCCESS, bits[2], bits[1], bits[0]);
+
+	memzero_explicit(bits, sizeof(bits));
+	return 1;
+}
+
+int kvm_trng_call(struct kvm_vcpu *vcpu)
+{
+	const __le32 *u = (__le32 *)arm_smc_trng_uuid.b;
+	u32 func_id = smccc_get_function(vcpu);
+	unsigned long val = TRNG_NOT_SUPPORTED;
+	int size = 64;
+
+	switch (func_id) {
+	case ARM_SMCCC_TRNG_VERSION:
+		val = ARM_SMCCC_TRNG_VERSION_1_0;
+		break;
+	case ARM_SMCCC_TRNG_FEATURES:
+		switch (smccc_get_arg1(vcpu)) {
+		case ARM_SMCCC_TRNG_VERSION:
+		case ARM_SMCCC_TRNG_FEATURES:
+		case ARM_SMCCC_TRNG_GET_UUID:
+		case ARM_SMCCC_TRNG_RND32:
+		case ARM_SMCCC_TRNG_RND64:
+			val = TRNG_SUCCESS;
+		}
+		break;
+	case ARM_SMCCC_TRNG_GET_UUID:
+		smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
+				 le32_to_cpu(u[2]), le32_to_cpu(u[3]));
+		return 1;
+	case ARM_SMCCC_TRNG_RND32:
+		size = 32;
+		fallthrough;
+	case ARM_SMCCC_TRNG_RND64:
+		return kvm_trng_do_rnd(vcpu, size);
+	}
+
+	smccc_set_retval(vcpu, val, 0, 0, 0);
+	return 1;
+}
-- 
2.17.1