Add support for Random extern to PSA/eBPF backend (#3251)

Co-authored-by: Mateusz Kossakowski <[email protected]>
Co-authored-by: Jan Palimąka <[email protected]>

backends/ebpf/CMakeLists.txt

@@ -48,6 +48,7 @@ set (P4C_EBPF_SRCS
   psa/externs/ebpfPsaChecksum.cpp
   psa/externs/ebpfPsaHashAlgorithm.cpp
   psa/externs/ebpfPsaTableImplementation.cpp
+  psa/externs/ebpfPsaRandom.cpp
   psa/externs/ebpfPsaRegister.cpp
   psa/externs/ebpfPsaMeter.cpp
 )
@@ -83,6 +84,7 @@ set (P4C_EBPF_HDRS
   psa/externs/ebpfPsaHashAlgorithm.h
   psa/externs/ebpfPsaTableImplementation.h
   psa/externs/ebpfPsaRegister.h
+  psa/externs/ebpfPsaRandom.h
   psa/externs/ebpfPsaMeter.h
 )
 

backends/ebpf/psa/README.md

@@ -299,6 +299,12 @@ for a given key exists. A value of the BPF map is ignored.
 **Note:** As of April 2022, support for value_set in `psabpf-ctl` CLI/API is not implemented yet. As a workaround you can
 use the `bpftool` command.
 
+### Random 
+
+The [Random](https://p4.org/p4-spec/docs/PSA.html#sec-random) extern is a mean to retrieve a pseudo-random number in a specified range within a P4 program.
+The PSA-eBPF compiler uses the `bpf_get_prandom_u32()` BPF helper to get a pseudo-random number. 
+Each `read()` operation on the Random extern in a P4 program is translated into a call to the BPF helper.
+
 # Getting started
 
 ## Installation 

backends/ebpf/psa/ebpfPsaControl.cpp

@@ -75,6 +75,10 @@ void ControlBodyTranslatorPSA::processMethod(const P4::ExternMethod* method) {
         auto hash = control->to<EBPFControlPSA>()->getHash(name);
         hash->processMethod(builder, method->method->name.name, method->expr, this);
         return;
+    } else if (declType->name.name == "Random") {
+        auto rand = control->to<EBPFControlPSA>()->getRandomExt(name);
+        rand->processMethod(builder, method);
+        return;
     } else if (declType->name.name == "Register") {
         auto reg = control->to<EBPFControlPSA>()->getRegister(name);
         if (method->method->type->name == "write") {

backends/ebpf/psa/ebpfPsaControl.h

@@ -20,6 +20,7 @@ limitations under the License.
 #include "ebpfPsaTable.h"
 #include "backends/ebpf/ebpfControl.h"
 #include "backends/ebpf/psa/externs/ebpfPsaChecksum.h"
+#include "backends/ebpf/psa/externs/ebpfPsaRandom.h"
 #include "backends/ebpf/psa/externs/ebpfPsaRegister.h"
 
 namespace EBPF {
@@ -64,6 +65,7 @@ class EBPFControlPSA : public EBPFControl {
     const IR::Parameter* outputStandardMetadata;
 
     std::map<cstring, EBPFHashPSA*> hashes;
+    std::map<cstring, EBPFRandomPSA*> randoms;
     std::map<cstring, EBPFRegisterPSA*>  registers;
     std::map<cstring, EBPFMeterPSA*>  meters;
 
@@ -76,6 +78,12 @@ class EBPFControlPSA : public EBPFControl {
     void emitTableInstances(CodeBuilder* builder) override;
     void emitTableInitializers(CodeBuilder* builder) override;
 
+    EBPFRandomPSA* getRandomExt(cstring name) const {
+        auto result = ::get(randoms, name);
+        BUG_CHECK(result != nullptr, "No random generator named %1%", name);
+        return result;
+    }
+
     EBPFRegisterPSA* getRegister(cstring name) const {
         auto result = ::get(registers, name);
         BUG_CHECK(result != nullptr, "No register named %1%", name);

backends/ebpf/psa/ebpfPsaGen.cpp

@@ -23,6 +23,7 @@ limitations under the License.
 #include "externs/ebpfPsaCounter.h"
 #include "externs/ebpfPsaHashAlgorithm.h"
 #include "externs/ebpfPsaTableImplementation.h"
+#include "externs/ebpfPsaRandom.h"
 #include "externs/ebpfPsaMeter.h"
 
 namespace EBPF {
@@ -693,6 +694,9 @@ bool ConvertToEBPFControlPSA::preorder(const IR::ExternBlock* instance) {
     } else if (typeName == "Counter") {
         auto ctr = new EBPFCounterPSA(program, di, name, control->codeGen);
         control->counters.emplace(name, ctr);
+    } else if (typeName == "Random") {
+        auto rand = new EBPFRandomPSA(di);
+        control->randoms.emplace(name, rand);
     } else if (typeName == "Register") {
         auto reg = new EBPFRegisterPSA(program, name, di, control->codeGen);
         control->registers.emplace(name, reg);

backends/ebpf/psa/externs/ebpfPsaRandom.cpp

@@ -0,0 +1,104 @@
+/*
+Copyright 2022-present Orange
+Copyright 2022-present Open Networking Foundation
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#include "ebpfPsaRandom.h"
+
+namespace EBPF {
+
+EBPFRandomPSA::EBPFRandomPSA(const IR::Declaration_Instance* di) :
+        minValue(0), maxValue(0), range(0) {
+    CHECK_NULL(di);
+
+    // verify type
+    if (!di->type->is<IR::Type_Specialized>()) {
+        ::error(ErrorType::ERR_MODEL, "Missing specialization: %1%", di);
+        return;
+    }
+    auto ts = di->type->to<IR::Type_Specialized>();
+    BUG_CHECK(ts->arguments->size() == 1, "%1%, Lack of specialization argument", ts);
+    auto type = ts->arguments->at(0);
+    if (!type->is<IR::Type_Bits>()) {
+        ::error(ErrorType::ERR_UNSUPPORTED, "Must be bit or int type: %1%", ts);
+        return;
+    }
+    if (type->width_bits()  > 32) {
+        ::error(ErrorType::ERR_UNSUPPORTED, "%1%: up to 32 bits width is supported", ts);
+    }
+
+    if (di->arguments->size() != 2) {
+        ::error(ErrorType::ERR_MODEL, "Expected 2 arguments to: %1%", di);
+        return;
+    }
+
+    unsigned tmp[2] = {0};
+    for (int i = 0; i < 2; ++i) {
+        auto expr = di->arguments->at(i)->expression->to<IR::Constant>();
+        if (expr != nullptr) {
+            if (expr->fitsUint()) {
+                tmp[i] = expr->asUnsigned();
+            } else {
+                ::error(ErrorType::ERR_OVERLIMIT, "%1%: size too large", expr);
+            }
+        } else {
+            ::error(ErrorType::ERR_UNSUPPORTED, "Must be constant value: %1%",
+                    di->arguments->at(i)->expression);
+        }
+    }
+
+    minValue = tmp[0];
+    maxValue = tmp[1];
+    range = (long) maxValue - minValue + 1;
+
+    // verify constructor parameters
+    if (minValue > maxValue) {
+        ::error(ErrorType::ERR_INVALID, "%1%: Max value lower than min value", di);
+    }
+    if (minValue == maxValue) {
+        ::warning(ErrorType::WARN_IGNORE,
+                  "%1%: No randomness, will always return the same value "
+                  "due to that the min value is equal to the max value", di);
+    }
+}
+
+void EBPFRandomPSA::processMethod(CodeBuilder* builder, const P4::ExternMethod* method) const {
+    if (method->method->type->name == "read") {
+        emitRead(builder);
+    } else {
+        ::error(ErrorType::ERR_UNSUPPORTED, "%1%: Method not implemented yet", method->expr);
+    }
+}
+
+void EBPFRandomPSA::emitRead(CodeBuilder* builder) const {
+    if (minValue == maxValue || range == 0) {
+        builder->append(minValue);
+        return;
+    }
+
+    bool rangeIsPowerOf2 = (range & (range - 1)) == 0;
+
+    if (minValue != 0)
+        builder->appendFormat("(%uu + ", minValue);
+
+    builder->append("(bpf_get_prandom_u32() ");
+    if (rangeIsPowerOf2) {
+        builder->appendFormat("& 0x%llxu", range - 1);
+    } else {
+        builder->appendFormat("%% %lluu", range);
+    }
+    builder->append(")");
+
+    if (minValue != 0)
+        builder->append(")");
+}
+
+}  // namespace EBPF

backends/ebpf/psa/externs/ebpfPsaRandom.h

@@ -0,0 +1,34 @@
+/*
+Copyright 2022-present Orange
+Copyright 2022-present Open Networking Foundation
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#ifndef BACKENDS_EBPF_PSA_EXTERNS_EBPFPSARANDOM_H_
+#define BACKENDS_EBPF_PSA_EXTERNS_EBPFPSARANDOM_H_
+
+#include "frontends/p4/methodInstance.h"
+#include "backends/ebpf/ebpfObject.h"
+
+namespace EBPF {
+
+class EBPFRandomPSA : public EBPFObject {
+    unsigned int minValue, maxValue;
+    long range;
+ public:
+    explicit EBPFRandomPSA(const IR::Declaration_Instance* di);
+
+    void processMethod(CodeBuilder* builder, const P4::ExternMethod* method) const;
+    void emitRead(CodeBuilder* builder) const;
+};
+
+}  // namespace EBPF
+
+#endif  // BACKENDS_EBPF_PSA_EXTERNS_EBPFPSARANDOM_H_

backends/ebpf/tests/p4testdata/random.p4

@@ -0,0 +1,96 @@
+/*
+Copyright 2022-present Orange
+Copyright 2022-present Open Networking Foundation
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#include <core.p4>
+#include <psa.p4>
+#include "common_headers.p4"
+
+header random_t {
+    bit<32> f1;
+    bit<16> f2;
+    bit<16> f3;
+}
+
+struct headers {
+    ethernet_t eth;
+    random_t   rand;
+}
+
+parser MyIP(packet_in buffer, out headers hdr, inout empty_t bp,
+            in psa_ingress_parser_input_metadata_t c, in empty_t d, in empty_t e) {
+    state start {
+        buffer.extract(hdr.eth);
+        buffer.extract(hdr.rand);
+        transition accept;
+    }
+}
+
+parser MyEP(packet_in buffer, out empty_t a, inout empty_t b,
+            in psa_egress_parser_input_metadata_t c, in empty_t d, in empty_t e, in empty_t f) {
+    state start {
+        transition accept;
+    }
+}
+
+control MyIC(inout headers a, inout empty_t bc,
+             in psa_ingress_input_metadata_t istd, inout psa_ingress_output_metadata_t ostd) {
+    Random(16w0, 16w127) r1;
+    Random<bit<32>>(0x80_00_00_01, 0x80_00_00_05) r2;
+    Random(16w256, 16w259) r3;
+
+    action do_forward(PortId_t egress_port) {
+        a.rand.f3 = r3.read();
+        send_to_port(ostd, egress_port);
+    }
+
+    table tbl_fwd {
+        key = {
+            istd.ingress_port : exact;
+        }
+        actions = { do_forward; NoAction; }
+        default_action = do_forward((PortId_t) 5);
+        size = 100;
+    }
+
+    apply {
+        a.rand.f1 = r2.read();
+        a.rand.f2 = r1.read();
+        tbl_fwd.apply();
+    }
+}
+
+control MyEC(inout empty_t a, inout empty_t b,
+    in psa_egress_input_metadata_t c, inout psa_egress_output_metadata_t d) {
+    apply { }
+}
+
+control MyID(packet_out buffer, out empty_t a, out empty_t b, out empty_t c,
+    inout headers d, in empty_t e, in psa_ingress_output_metadata_t f) {
+    apply {
+        buffer.emit(d.eth);
+        buffer.emit(d.rand);
+    }
+}
+
+control MyED(packet_out buffer, out empty_t a, out empty_t b, inout empty_t c, in empty_t d,
+    in psa_egress_output_metadata_t e, in psa_egress_deparser_input_metadata_t f) {
+    apply { }
+}
+
+IngressPipeline(MyIP(), MyIC(), MyID()) ip;
+EgressPipeline(MyEP(), MyEC(), MyED()) ep;
+
+PSA_Switch(ip, PacketReplicationEngine(), ep, BufferingQueueingEngine()) main;

backends/ebpf/tests/ptf/test.py

@@ -432,6 +432,58 @@ def runTest(self):
         testutils.verify_no_other_packets(self)
 
 
+# xdp2tc=head is not supported because pkt_len of test packet (Ethernet+RandomHeader) < 34 B
+@xdp2tc_head_not_supported
+class RandomPSATest(P4EbpfTest):
+    """
+    Read random data generated by data plane.
+    Verify that random values are in the expected range.
+    """
+    p4_file_path = "p4testdata/random.p4"
+
+    class RandomHeader(Packet):
+        name = "random"
+        fields_desc = [
+            IntField("f1", 0),
+            ShortField("f2", 0),
+            ShortField("f3", 0)
+        ]
+
+    def setUp(self):
+        super(RandomPSATest, self).setUp()
+        bind_layers(Ether, self.RandomHeader, type=0x801)
+
+    def tearDown(self):
+        split_layers(Ether, self.RandomHeader, type=0x801)
+        super(RandomPSATest, self).tearDown()
+
+    def verify_range(self, value, min_value, max_value):
+        if value < min_value or value > max_value:
+            self.fail("Value {} out of range [{}, {}]".format(value, min_value, max_value))
+
+    def runTest(self):
+        self.table_add(table="MyIC_tbl_fwd", keys=[4], action=1, data=[5])
+        pkt = Ether() / self.RandomHeader()
+        mask = Mask(pkt)
+        mask.set_do_not_care_scapy(self.RandomHeader, "f1")
+        mask.set_do_not_care_scapy(self.RandomHeader, "f2")
+        mask.set_do_not_care_scapy(self.RandomHeader, "f3")
+        sequence = [[], [], []]
+        for _ in range(10):
+            testutils.send_packet(self, PORT0, pkt)
+            (_, recv_pkt) = testutils.verify_packet_any_port(self, mask, ALL_PORTS)
+            recv_pkt = Ether(recv_pkt)
+            self.verify_range(value=recv_pkt[self.RandomHeader].f1, min_value=0x80_00_00_01, max_value=0x80_00_00_05)
+            sequence[0].append(recv_pkt[self.RandomHeader].f1)
+            self.verify_range(value=recv_pkt[self.RandomHeader].f2, min_value=0, max_value=127)
+            sequence[1].append(recv_pkt[self.RandomHeader].f2)
+            self.verify_range(value=recv_pkt[self.RandomHeader].f3, min_value=256, max_value=259)
+            sequence[2].append(recv_pkt[self.RandomHeader].f3)
+        logger.info("f1 sequence: {}".format(sequence[0]))
+        logger.info("f2 sequence: {}".format(sequence[1]))
+        logger.info("f3 sequence: {}".format(sequence[2]))
+
+
 class VerifyPSATest(P4EbpfTest):
     p4_file_path = "p4testdata/verify.p4"