Re: [PATCH] eal: add support for TRNG with Arm RNG feature

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-07-24 16:35, Stephen Hemminger wrote:
> On Wed, 24 Jul 2024 08:40:39 +0200
> Mattias Rönnblom <hofors@lysator.liu.se> wrote:
> 
>> On 2024-07-23 23:27, Shunzhi Wen wrote:> True Random Number Generator
>> (TRNG) is capable of
>>   > generating random numbers from a physical entropy source.
>>   > TRNG is enabled when compiled on Arm arch that supports
>>   > FEAT_RNG introduced in Armv8.5-A flagged by __ARM_FEATURE_RNG.
>>   >
>>
>> I'm missing a rationale here. Why is this useful?
>>
>>   > Signed-off-by: Shunzhi Wen <shunzhi.wen@arm.com>
>>   > Reviewed-by: Wathsala Vithanage <wathsala.vithanage@arm.com>
>>   > Reviewed-by: Jack Bond-Preston <jack.bond-preston@arm.com>
>>   > Reviewed-by: Dhruv Tripathi <dhruv.tripathi@arm.com>
>>   > ---
>>   >   .mailmap                                      |  2 ++
>>   >   app/test/test_rand_perf.c                     | 25 +++++++++++++++++--
>>   >   config/arm/meson.build                        |  2 +-
>>   >   lib/eal/arm/include/rte_cpuflags_64.h         |  3 +++
>>   >   lib/eal/arm/meson.build                       |  1 +
>>   >   lib/eal/arm/rte_cpuflags.c                    |  1 +
>>   >   lib/eal/arm/rte_random.c                      | 20 +++++++++++++++
>>   >   .../{rte_random.c => eal_common_random.c}     |  0
>>   >   lib/eal/common/meson.build                    |  2 +-
>>   >   lib/eal/include/rte_random.h                  | 17 +++++++++++++
>>   >   lib/eal/loongarch/meson.build                 |  1 +
>>   >   lib/eal/loongarch/rte_random.c                | 14 +++++++++++
>>   >   lib/eal/ppc/meson.build                       |  1 +
>>   >   lib/eal/ppc/rte_random.c                      | 14 +++++++++++
>>   >   lib/eal/riscv/meson.build                     |  1 +
>>   >   lib/eal/riscv/rte_random.c                    | 14 +++++++++++
>>   >   lib/eal/version.map                           |  1 +
>>   >   lib/eal/x86/meson.build                       |  1 +
>>   >   lib/eal/x86/rte_random.c                      | 14 +++++++++++
>>   >   19 files changed, 130 insertions(+), 4 deletions(-)
>>   >   create mode 100644 lib/eal/arm/rte_random.c
>>   >   rename lib/eal/common/{rte_random.c => eal_common_random.c} (100%)
>>   >   create mode 100644 lib/eal/loongarch/rte_random.c
>>   >   create mode 100644 lib/eal/ppc/rte_random.c
>>   >   create mode 100644 lib/eal/riscv/rte_random.c
>>   >   create mode 100644 lib/eal/x86/rte_random.c
>>   >
>>   > diff --git a/.mailmap b/.mailmap
>>   > index ac06962e82..23209edfd2 100644
>>   > --- a/.mailmap
>>   > +++ b/.mailmap
>>   > @@ -338,6 +338,7 @@ Dexia Li <dexia.li@jaguarmicro.com>
>>   >   Dexuan Cui <decui@microsoft.com>
>>   >   Dharmik Thakkar <dharmikjayesh.thakkar@arm.com>
>> <dharmik.thakkar@arm.com>
>>   >   Dheemanth Mallikarjun <dheemanthm@vmware.com>
>>   > +Dhruv Tripathi <dhruv.tripathi@arm.com>
>>   >   Diana Wang <na.wang@corigine.com>
>>   >   Didier Pallard <didier.pallard@6wind.com>
>>   >   Dilshod Urazov <dilshod.urazov@oktetlabs.ru>
>>   > @@ -1353,6 +1354,7 @@ Shuki Katzenelson <shuki@lightbitslabs.com>
>>   >   Shun Hao <shunh@nvidia.com>
>>   >   Shu Shen <shu.shen@radisys.com>
>>   >   Shujing Dong <shujing.dong@corigine.com>
>>   > +Shunzhi Wen <shunzhi.wen@arm.com>
>>   >   Shweta Choudaha <shweta.choudaha@att.com>
>>   >   Shyam Kumar Shrivastav <shrivastav.shyam@gmail.com>
>>   >   Shy Shyman <shys@nvidia.com> <shys@mellanox.com>
>>   > diff --git a/app/test/test_rand_perf.c b/app/test/test_rand_perf.c
>>   > index 30204e12c0..b61cc75014 100644
>>   > --- a/app/test/test_rand_perf.c
>>   > +++ b/app/test/test_rand_perf.c
>>   > @@ -20,6 +20,7 @@ static volatile uint64_t vsum;
>>   >
>>   >   enum rand_type {
>>   >   	rand_type_64,
>>   > +	rand_type_true_rand_64,
>>   >   	rand_type_float,
>>   >   	rand_type_bounded_best_case,
>>   >   	rand_type_bounded_worst_case
>>   > @@ -31,6 +32,8 @@ rand_type_desc(enum rand_type rand_type)
>>   >   	switch (rand_type) {
>>   >   	case rand_type_64:
>>   >   		return "Full 64-bit [rte_rand()]";
>>   > +	case rand_type_true_rand_64:
>>   > +		return "Full 64-bit True Random [rte_trand()]";
>>   >   	case rand_type_float:
>>   >   		return "Floating point [rte_drand()]";
>>   >   	case rand_type_bounded_best_case:
>>   > @@ -50,6 +53,9 @@ test_rand_perf_type(enum rand_type rand_type)
>>   >   	uint64_t end;
>>   >   	uint64_t sum = 0;
>>   >   	uint64_t op_latency;
>>   > +	int ret;
>>   > +	uint64_t val;
>>   > +	uint32_t fail_count = 0;
>>   >
>>   >   	start = rte_rdtsc();
>>   >
>>   > @@ -58,6 +64,13 @@ test_rand_perf_type(enum rand_type rand_type)
>>   >   		case rand_type_64:
>>   >   			sum += rte_rand();
>>   >   			break;
>>   > +		case rand_type_true_rand_64:
>>   > +			ret = rte_trand(&val);
>>   > +			if (ret == 0)
>>   > +				sum += val;
>>   > +			else
>>   > +				fail_count++;
>>   > +			break;
>>   >   		case rand_type_float:
>>   >   			sum += 1000. * rte_drand();
>>   >   			break;
>>   > @@ -77,8 +90,15 @@ test_rand_perf_type(enum rand_type rand_type)
>>   >
>>   >   	op_latency = (end - start) / ITERATIONS;
>>   >
>>   > -	printf("%s: %"PRId64" TSC cycles/op\n", rand_type_desc(rand_type),
>>   > -	       op_latency);
>>   > +	if (!fail_count)
>>   > +		printf("%s: %"PRId64" TSC cycles/op\n",
>>   > +		       rand_type_desc(rand_type),
>>   > +		       op_latency);
>>   > +	else
>>   > +		printf("%s: %"PRId64" TSC cycles/op (failed %d time(s))\n",
>>   > +		       rand_type_desc(rand_type),
>>   > +		       op_latency,
>>   > +			   fail_count);
>>   >   }
>>   >
>>   >   static int
>>   > @@ -89,6 +109,7 @@ test_rand_perf(void)
>>   >   	printf("Pseudo-random number generation latencies:\n");
>>   >
>>   >   	test_rand_perf_type(rand_type_64);
>>   > +	test_rand_perf_type(rand_type_true_rand_64);
>>   >   	test_rand_perf_type(rand_type_float);
>>   >   	test_rand_perf_type(rand_type_bounded_best_case);
>>   >   	test_rand_perf_type(rand_type_bounded_worst_case);
>>   > diff --git a/config/arm/meson.build b/config/arm/meson.build
>>   > index 012935d5d7..13be94254e 100644
>>   > --- a/config/arm/meson.build
>>   > +++ b/config/arm/meson.build
>>   > @@ -95,7 +95,7 @@ part_number_config_arm = {
>>   >       },
>>   >       '0xd49': {
>>   >           'march': 'armv9-a',
>>   > -        'march_features': ['sve2'],
>>   > +        'march_features': ['sve2', 'rng'],
>>   >           'fallback_march': 'armv8.5-a',
>>   >           'mcpu': 'neoverse-n2',
>>   >           'flags': [
>>   > diff --git a/lib/eal/arm/include/rte_cpuflags_64.h
>> b/lib/eal/arm/include/rte_cpuflags_64.h
>>   > index afe70209c3..6aa067339f 100644
>>   > --- a/lib/eal/arm/include/rte_cpuflags_64.h
>>   > +++ b/lib/eal/arm/include/rte_cpuflags_64.h
>>   > @@ -36,6 +36,9 @@ enum rte_cpu_flag_t {
>>   >   	RTE_CPUFLAG_SVEF64MM,
>>   >   	RTE_CPUFLAG_SVEBF16,
>>   >   	RTE_CPUFLAG_AARCH64,
>>   > +
>>   > +	/* RNDR, RNDRRS instructions */
>>   > +	RTE_CPUFLAG_RNG,
>>   >   };
>>   >
>>   >   #include "generic/rte_cpuflags.h"
>>   > diff --git a/lib/eal/arm/meson.build b/lib/eal/arm/meson.build
>>   > index 6fba3d6ba7..e9e468cbf0 100644
>>   > --- a/lib/eal/arm/meson.build
>>   > +++ b/lib/eal/arm/meson.build
>>   > @@ -9,4 +9,5 @@ sources += files(
>>   >           'rte_hypervisor.c',
>>   >           'rte_mmu.c',
>>   >           'rte_power_intrinsics.c',
>>   > +        'rte_random.c',
>>   >   )
>>   > diff --git a/lib/eal/arm/rte_cpuflags.c b/lib/eal/arm/rte_cpuflags.c
>>   > index 7ba4f8ba97..56074f0c6a 100644
>>   > --- a/lib/eal/arm/rte_cpuflags.c
>>   > +++ b/lib/eal/arm/rte_cpuflags.c
>>   > @@ -116,6 +116,7 @@ const struct feature_entry
>> rte_cpu_feature_table[] = {
>>   >   	FEAT_DEF(SVEF64MM,	REG_HWCAP2,   11)
>>   >   	FEAT_DEF(SVEBF16,	REG_HWCAP2,   12)
>>   >   	FEAT_DEF(AARCH64,	REG_PLATFORM,  0)
>>   > +	FEAT_DEF(RNG,		REG_HWCAP2,   16)
>>   >   };
>>   >   #endif /* RTE_ARCH */
>>   >
>>   > diff --git a/lib/eal/arm/rte_random.c b/lib/eal/arm/rte_random.c
>>   > new file mode 100644
>>   > index 0000000000..74c8fa733b
>>   > --- /dev/null
>>   > +++ b/lib/eal/arm/rte_random.c
>>   > @@ -0,0 +1,20 @@
>>   > +/* SPDX-License-Identifier: BSD-3-Clause
>>   > + * Copyright(c) 2024 Arm Limited
>>   > + */
>>   > +
>>   > +#include "arm_acle.h"
>>   > +#include "rte_common.h"
>>   > +#include "rte_random.h"
>>   > +#include <errno.h>
>>   > +
>>   > +int
>>   > +rte_trand(uint64_t *val)
>>   > +{
>>   > +#if defined __ARM_FEATURE_RNG
>>   > +	int ret = __rndr(val);
>>   > +	return (ret == 0) ? 0 : -ENODATA;
>>   > +#else
>>   > +	RTE_SET_USED(val);
>>   > +	return -ENOTSUP;
>>   > +#endif
>>   > +}
>>   > diff --git a/lib/eal/common/rte_random.c
>> b/lib/eal/common/eal_common_random.c
>>   > similarity index 100%
>>   > rename from lib/eal/common/rte_random.c
>>   > rename to lib/eal/common/eal_common_random.c
>>   > diff --git a/lib/eal/common/meson.build b/lib/eal/common/meson.build
>>   > index 22a626ba6f..c4405aa48b 100644
>>   > --- a/lib/eal/common/meson.build
>>   > +++ b/lib/eal/common/meson.build
>>   > @@ -32,7 +32,6 @@ sources += files(
>>   >           'malloc_elem.c',
>>   >           'malloc_heap.c',
>>   >           'rte_malloc.c',
>>   > -        'rte_random.c',
>>   >           'rte_reciprocal.c',
>>   >           'rte_service.c',
>>   >           'rte_version.c',
>>   > @@ -48,6 +47,7 @@ if not is_windows
>>   >               'eal_common_trace.c',
>>   >               'eal_common_trace_ctf.c',
>>   >               'eal_common_trace_utils.c',
>>   > +            'eal_common_random.c',
>>   >               'hotplug_mp.c',
>>   >               'malloc_mp.c',
>>   >               'rte_keepalive.c',
>>   > diff --git a/lib/eal/include/rte_random.h b/lib/eal/include/rte_random.h
>>   > index 5031c6fe5f..e6b5ac46ed 100644
>>   > --- a/lib/eal/include/rte_random.h
>>   > +++ b/lib/eal/include/rte_random.h
>>   > @@ -15,6 +15,7 @@
>>   >   extern "C" {
>>   >   #endif
>>   >
>>   > +#include <rte_compat.h>
>>   >   #include <stdint.h>
>>   >
>>   >   /**
>>   > @@ -84,6 +85,22 @@ rte_rand_max(uint64_t upper_bound);
>>   >    */
>>   >   double rte_drand(void);
>>   >
>>   > +/**
>>   > + * Get a true random value.
>>   > + *
>>   > + * The generator is cryptographically secure.
>>
>> If you want to extend <rte_random.h> with a cryptographically secure
>> random number generator, that's fine.
>>
>> To have an API that's only available on certain ARM CPUs is not.
>>
>> NAK
>>
>> A new function should be called something with "secure", rather than
>> "true" (which is a bit silly, since we might well live in a completely
>> deterministic universe). "secure" would more clearly communicate the
>> intent, and also doesn't imply any particular implementation.
> 
> Agree, with Mattias. What constitutes a secure random number generator
> is a matter of much debate. Most of the HW random generators are taking
> diode (Schottky noise) and doing transforms on it to get something uniform.
> 
> If a key generation type API was added, why not just use existing and more
> researched kernel get_random()?
> 

Ideally, you want to avoid system calls on lcore workers doing packet 
processing. If you have to do system calls (which I believe is the case 
here), it's better to a simple call, not so often.

getentropy() seems to need about 800 core clock cycles on my x86_64, on 
average. (rte_rand() needs ~11 cc/call.) 800 cc is not too horrible, but 
system calls tend to have some pretty bad tail latencies.

To improve efficiency, one could do a getentropy() on a relatively large 
buffer, and cache the result on a per-lcore basis, amortizing the system 
call overhead over many calls.

You still have the tail latency issue to deal with. We could have a 
control thread providing entropy for the lcores, but that seems like 
massive overkill.