Helper reallocate packet (microsoft#3110)

* add reallocate_packet flag to helper prototype struct.

* PR Feedback.

* fix.

* export reallocate_packet flag.

docs/eBpfExtensions.md

@@ -130,6 +130,7 @@ Helper function IDs for different program types need not be unique.
 * `return_type`: Set the appropriate value for the `ebpf_return_type_t` enum that represents the return type of the
 helper function.
 * `arguments`: Array of (at most) five helper function arguments of type `ebpf_argument_type_t`.
+* `reallocate_packet`: Flag indicating if this helper function performs packet reallocation.
 
 #### `ebpf_argument_type_t` Enum
 This enum describes the various argument types that can be passed to an eBPF helper function. This is defined in the

include/ebpf_program_types.h

@@ -7,12 +7,14 @@
 
 #include <guiddef.h>
 #if !defined(NO_CRT) && !defined(_NO_CRT_STDIO_INLINE)
+#include <stdbool.h>
 #include <stdint.h>
 #else
 typedef unsigned char uint8_t;
 typedef unsigned int uint32_t;
 typedef unsigned long long uint64_t;
 typedef unsigned short wchar_t;
+#define bool _Bool
 #endif
 
 #define EBPF_MAX_PROGRAM_DESCRIPTOR_NAME_LENGTH 256
@@ -27,12 +29,15 @@ typedef struct _ebpf_program_type_descriptor
     char is_privileged;
 } ebpf_program_type_descriptor_t;
 
+#define HELPER_FUNCTION_REALLOCATE_PACKET 0x1
+
 typedef struct _ebpf_helper_function_prototype
 {
     uint32_t helper_id;
     const char* name;
     ebpf_return_type_t return_type;
     ebpf_argument_type_t arguments[5];
+    bool reallocate_packet : 1;
 } ebpf_helper_function_prototype_t;
 
 typedef struct _ebpf_program_info

libs/api_common/store_helper_internal.cpp

@@ -50,8 +50,9 @@ _load_helper_prototype(
 
         // Read serialized helper prototype information.
         char serialized_data[sizeof(ebpf_helper_function_prototype_t)] = {0};
+        bool reallocate_packet = false;
         size_t expected_size = sizeof(helper_prototype->helper_id) + sizeof(helper_prototype->return_type) +
-                               sizeof(helper_prototype->arguments);
+                               sizeof(helper_prototype->arguments) + sizeof(reallocate_packet);
 
         status = ebpf_read_registry_value_binary(
             helper_info_key, EBPF_HELPER_DATA_PROTOTYPE, (uint8_t*)serialized_data, expected_size);
@@ -71,6 +72,10 @@ _load_helper_prototype(
         memcpy(&helper_prototype->arguments, serialized_data + offset, sizeof(helper_prototype->arguments));
         offset += sizeof(helper_prototype->arguments);
 
+        memcpy(&reallocate_packet, serialized_data + offset, sizeof(reallocate_packet));
+        helper_prototype->reallocate_packet = reallocate_packet ? HELPER_FUNCTION_REALLOCATE_PACKET : 0;
+        offset += sizeof(reallocate_packet);
+
         helper_prototype->name =
             cxplat_duplicate_string(ebpf_down_cast_from_wstring(std::wstring(helper_name)).c_str());
         if (helper_prototype->name == nullptr) {

libs/api_common/windows_helpers.cpp

@@ -61,5 +61,7 @@ get_helper_prototype_windows(int32_t n)
         verifier_prototype.argument_type[i] = raw_prototype->arguments[i];
     }
 
+    verifier_prototype.reallocate_packet = raw_prototype->reallocate_packet == TRUE;
+
     return verifier_prototype;
 }

libs/execution_context/ebpf_program.c

@@ -2063,6 +2063,7 @@ _IRQL_requires_max_(PASSIVE_LEVEL) static ebpf_result_t _ebpf_program_compute_pr
     //   b. Helper name.
     //   c. Helper return type.
     //   d. Helper argument types.
+    //   e. reallocate_packet flag (if set).
 
     // Note:
     // Order and fields being hashed is important. The order and fields being hashed must match the order and fields
@@ -2128,6 +2129,13 @@ _IRQL_requires_max_(PASSIVE_LEVEL) static ebpf_result_t _ebpf_program_compute_pr
                 goto Exit;
             }
         }
+
+        if (helper_function_prototype->reallocate_packet) {
+            result = EBPF_CRYPTOGRAPHIC_HASH_APPEND_STR(cryptographic_hash, "reallocate_packet");
+            if (result != EBPF_SUCCESS) {
+                goto Exit;
+            }
+        }
     }
     *hash_length = 0;
     result = ebpf_cryptographic_hash_get_hash_length(cryptographic_hash, hash_length);

libs/shared/ebpf_serialize.c

@@ -29,6 +29,7 @@ typedef struct _ebpf_serialized_helper_function_prototype
     uint32_t helper_id;
     ebpf_return_type_t return_type;
     ebpf_argument_type_t arguments[5];
+    uint8_t reallocate_packet;
     size_t name_length;
     uint8_t name[1];
 } ebpf_serialized_helper_function_prototype_t;
@@ -462,6 +463,8 @@ ebpf_serialize_program_info(
             for (uint16_t index = 0; index < EBPF_COUNT_OF(helper_prototype->arguments); index++) {
                 serialized_helper_prototype->arguments[index] = helper_prototype->arguments[index];
             }
+            serialized_helper_prototype->reallocate_packet =
+                helper_prototype->reallocate_packet ? HELPER_FUNCTION_REALLOCATE_PACKET : 0;
             serialized_helper_prototype->name_length = helper_function_name_length;
             // Copy the program type descriptor name buffer.
             memcpy(serialized_helper_prototype->name, helper_prototype->name, helper_function_name_length);
@@ -627,12 +630,14 @@ ebpf_deserialize_program_info(
             goto Exit;
         }
 
-        // Serialize helper prototype.
+        // Deserialize helper prototype.
         helper_prototype->helper_id = serialized_helper_prototype->helper_id;
         helper_prototype->return_type = serialized_helper_prototype->return_type;
         for (int i = 0; i < EBPF_COUNT_OF(helper_prototype->arguments); i++) {
             helper_prototype->arguments[i] = serialized_helper_prototype->arguments[i];
         }
+        helper_prototype->reallocate_packet =
+            serialized_helper_prototype->reallocate_packet == HELPER_FUNCTION_REALLOCATE_PACKET;
 
         // Adjust remaining buffer length.
         result = ebpf_safe_size_t_subtract(

libs/store_helper/ebpf_store_helper.c

@@ -1,7 +1,6 @@
 // Copyright (c) Microsoft Corporation
 // SPDX-License-Identifier: MIT
 
-#include "ebpf_program_types.h"
 #include "ebpf_registry_helper.h"
 #include "ebpf_store_helper.h"
 #include "ebpf_windows.h"
@@ -41,6 +40,7 @@ _ebpf_store_update_helper_prototype(
     uint32_t offset;
     ebpf_store_key_t helper_function_key = NULL;
     char serialized_data[sizeof(ebpf_helper_function_prototype_t)] = {0};
+    const bool reallocate_packet = helper_info->reallocate_packet;
 
     wchar_t* wide_helper_name = ebpf_get_wstring_from_string(helper_info->name);
     if (wide_helper_name == NULL) {
@@ -63,6 +63,9 @@ _ebpf_store_update_helper_prototype(
     memcpy(serialized_data + offset, helper_info->arguments, sizeof(helper_info->arguments));
     offset += sizeof(helper_info->arguments);
 
+    memcpy(serialized_data + offset, &reallocate_packet, sizeof(reallocate_packet));
+    offset += sizeof(reallocate_packet);
+
     // Save the helper prototype data.
     result = ebpf_write_registry_value_binary(
         helper_function_key, EBPF_HELPER_DATA_PROTOTYPE, (uint8_t*)&serialized_data[0], offset);

libs/store_helper/kernel/ebpf_store_helper_km.vcxproj

@@ -113,7 +113,7 @@
     <ClCompile>
       <WarningLevel>Level3</WarningLevel>
       <SDLCheck>true</SDLCheck>
-      <PreprocessorDefinitions>_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>_DEBUG;_LIB;_NO_CRT_STDIO_INLINE=1;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <ConformanceMode>true</ConformanceMode>
       <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <AdditionalIncludeDirectories>$(SolutionDir)libs/shared;$(SolutionDir)libs/shared/kernel;$(SolutionDir)libs/runtime;$(SolutionDir)libs/runtime/kernel;$(SolutionDir)external\usersim\cxplat\inc;$(SolutionDir)external\usersim\cxplat\inc\winkernel;$(IntDir);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
@@ -127,7 +127,7 @@
     <ClCompile>
       <WarningLevel>Level3</WarningLevel>
       <SDLCheck>true</SDLCheck>
-      <PreprocessorDefinitions>_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>_DEBUG;_LIB;_NO_CRT_STDIO_INLINE=1;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <ConformanceMode>true</ConformanceMode>
       <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <AdditionalIncludeDirectories>$(SolutionDir)libs/shared;$(SolutionDir)libs/shared/kernel;$(SolutionDir)libs/runtime;$(SolutionDir)libs/runtime/kernel;$(SolutionDir)external\usersim\cxplat\inc;$(SolutionDir)external\usersim\cxplat\inc\winkernel;$(IntDir);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>

netebpfext/net_ebpf_ext_program_info.h

@@ -14,7 +14,8 @@ static const ebpf_helper_function_prototype_t _xdp_test_ebpf_extension_helper_fu
     {XDP_EXT_HELPER_FUNCTION_START + 1,
      "bpf_xdp_adjust_head",
      EBPF_RETURN_TYPE_INTEGER,
-     {EBPF_ARGUMENT_TYPE_PTR_TO_CTX, EBPF_ARGUMENT_TYPE_ANYTHING}}};
+     {EBPF_ARGUMENT_TYPE_PTR_TO_CTX, EBPF_ARGUMENT_TYPE_ANYTHING},
+     HELPER_FUNCTION_REALLOCATE_PACKET}};
 
 // XDP_TEST program information.
 static const ebpf_context_descriptor_t _ebpf_xdp_test_context_descriptor = {

tests/end_to_end/netsh_test.cpp

@@ -356,6 +356,29 @@ TEST_CASE("show verification droppacket_unsafe.o", "[netsh][verification]")
                   "\n");
 }
 
+TEST_CASE("show verification xdp_adjust_head_unsafe.o", "[netsh][verification]")
+{
+    _test_helper_netsh test_helper;
+    test_helper.initialize();
+
+    int result;
+    std::string output =
+        _run_netsh_command(handle_ebpf_show_verification, L"xdp_adjust_head_unsafe.o", L"xdp", nullptr, &result);
+    REQUIRE(result == ERROR_SUPPRESS_OUTPUT);
+    output = strip_paths(output);
+    REQUIRE(
+        output == "Verification failed\n"
+                  "\n"
+                  "Verification report:\n"
+                  "\n"
+                  "; ./tests/sample/unsafe/xdp_adjust_head_unsafe.c:42\n"
+                  ";     ethernet_header->Type = 0x0800;\n"
+                  "17: Upper bound must be at most packet_size (valid_access(r1.offset+12, width=2) for write)\n"
+                  "\n"
+                  "1 errors\n"
+                  "\n");
+}
+
 TEST_CASE("show verification printk_unsafe.o", "[netsh][verification]")
 {
     _test_helper_netsh test_helper;

tests/sample/unsafe/xdp_adjust_head_unsafe.c

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation
+// SPDX-License-Identifier: MIT
+
+// clang -O2 -Werror -c xdp_adjust_head_unsafe.c -o xdp_adjust_head_unsafe_jit.o
+//
+// For bpf code: clang -target bpf -O2 -Werror -c xdp_adjust_head_unsafe.c -o xdp_adjust_head_unsafe.o
+//
+
+#include "bpf_endian.h"
+#include "bpf_helpers.h"
+#include "net/if_ether.h"
+#include "net/ip.h"
+#include "net/udp.h"
+
+SEC("xdp")
+int
+xdp_adjust_head_unsafe(xdp_md_t* ctx)
+{
+    int rc = XDP_PASS;
+
+    ETHERNET_HEADER* ethernet_header = NULL;
+    char* next_header = (char*)ctx->data;
+
+    // Access the Ethernet header fields after checking for safety.
+    // This will pass verifier test.
+    if (next_header + sizeof(ETHERNET_HEADER) > (char*)ctx->data_end) {
+        rc = XDP_DROP;
+        goto Done;
+    }
+    ethernet_header = (ETHERNET_HEADER*)next_header;
+    ethernet_header->Type = 0x0800;
+
+    // Adjust the head of the packet by removing the Ethernet header.
+    if (bpf_xdp_adjust_head(ctx, sizeof(ETHERNET_HEADER)) < 0) {
+        rc = XDP_DROP;
+        goto Done;
+    }
+
+    // Access the packet without checking for safety.
+    // This will fail verifier test.
+    ethernet_header = (ETHERNET_HEADER*)ctx->data;
+    ethernet_header->Type = 0x0800;
+
+Done:
+    return rc;
+}

tools/bpf2c/bpf2c.cpp

@@ -116,6 +116,9 @@ get_program_info_type_hash(const std::vector<int32_t>& actual_helper_ids, const
                 hash_t::append_byte_range(
                     byte_range, program_info->program_type_specific_helper_prototype[index].arguments[argument]);
             }
+            if (program_info->program_type_specific_helper_prototype[index].reallocate_packet) {
+                hash_t::append_byte_range(byte_range, reinterpret_cast<const char*>("reallocate_packet"));
+            }
         }
     }
     hash_t hash(algorithm);

tools/bpf2c/bpf2c.vcxproj

@@ -86,13 +86,13 @@
   </ImportGroup>
   <PropertyGroup Label="UserMacros" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
-    <LinkIncremental>true</LinkIncremental>
+    <LinkIncremental>false</LinkIncremental>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='NativeOnlyDebug|x64'">
-    <LinkIncremental>true</LinkIncremental>
+    <LinkIncremental>false</LinkIncremental>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='FuzzerDebug|x64'">
-    <LinkIncremental>true</LinkIncremental>
+    <LinkIncremental>false</LinkIncremental>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
     <LinkIncremental>false</LinkIncremental>
@@ -108,7 +108,7 @@
     </ClCompile>
     <Link>
       <SubSystem>Console</SubSystem>
-      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <GenerateDebugInformation>DebugFull</GenerateDebugInformation>
       <AdditionalDependencies>$(FuzzerLibs);%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
     <PreBuildEvent>
@@ -126,7 +126,7 @@
     </ClCompile>
     <Link>
       <SubSystem>Console</SubSystem>
-      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <GenerateDebugInformation>DebugFull</GenerateDebugInformation>
       <AdditionalDependencies>$(FuzzerLibs);%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
     <PreBuildEvent>
@@ -141,7 +141,7 @@
     </ClCompile>
     <Link>
       <SubSystem>Console</SubSystem>
-      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <GenerateDebugInformation>DebugFull</GenerateDebugInformation>
       <AdditionalDependencies>$(FuzzerLibs);%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
     <PreBuildEvent>
@@ -159,7 +159,7 @@
       <SubSystem>Console</SubSystem>
       <EnableCOMDATFolding>true</EnableCOMDATFolding>
       <OptimizeReferences>true</OptimizeReferences>
-      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <GenerateDebugInformation>DebugFull</GenerateDebugInformation>
       <AdditionalDependencies>$(FuzzerLibs);%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
     <PreBuildEvent>
@@ -177,7 +177,7 @@
       <SubSystem>Console</SubSystem>
       <EnableCOMDATFolding>true</EnableCOMDATFolding>
       <OptimizeReferences>true</OptimizeReferences>
-      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <GenerateDebugInformation>DebugFull</GenerateDebugInformation>
       <AdditionalDependencies>$(FuzzerLibs);%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
     <PreBuildEvent>