bpf loader improvements for better long term compatibility with mainline
This is bpfLoader v0.1, previously we had no version number, the version immediately preceding this commit we'll call v0.0. Versions older than that are either pre-S and don't matter, since loading mainline eBpf code was only added in S, or are from early during the S development cycle (ie. pre-March 5th 2021 or earlier) and simply no longer supported (no need to maintain compatibility). Bug: 190519702 Test: atest, TreeHugger - existing bpf programs load examination of bpfloader logs Signed-off-by: Maciej Żenczykowski <maze@google.com> Change-Id: I36fa5b917540be7ea3ecfddc5fe7834e9eb18d88
This commit is contained in:
Maciej Żenczykowski
parent
80f73b878b
commit
9217eee3df
3 changed files with 225 additions and 14 deletions
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@ -28,6 +28,12 @@
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#include <sys/utsname.h>
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#include <unistd.h>
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// This is BpfLoader 0.1, we need to define this prior to including bpf_map_def.h
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// to get the 0.1 struct definitions
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#define BPFLOADER_VERSION_MAJOR 0u
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#define BPFLOADER_VERSION_MINOR 1u
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#define BPFLOADER_VERSION ((BPFLOADER_VERSION_MAJOR << 16) | BPFLOADER_VERSION_MINOR)
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#include "../progs/include/bpf_map_def.h"
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#include "bpf/BpfUtils.h"
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#include "include/libbpf_android.h"
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@ -205,6 +211,29 @@ static int readSectionByName(const char* name, ifstream& elfFile, vector<char>&
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return -2;
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}
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static unsigned int readSectionUint(const char* name, ifstream& elfFile, unsigned int defVal) {
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vector<char> theBytes;
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int ret = readSectionByName(name, elfFile, theBytes);
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if (ret) {
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ALOGD("Couldn't find section %s (defaulting to %u [0x%x]).\n", name, defVal, defVal);
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return defVal;
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} else if (theBytes.size() < sizeof(unsigned int)) {
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ALOGE("Section %s too short (defaulting to %u [0x%x]).\n", name, defVal, defVal);
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return defVal;
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} else {
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// decode first 4 bytes as LE32 uint, there will likely be more bytes due to alignment.
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unsigned int value = static_cast<unsigned char>(theBytes[3]);
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value <<= 8;
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value += static_cast<unsigned char>(theBytes[2]);
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value <<= 8;
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value += static_cast<unsigned char>(theBytes[1]);
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value <<= 8;
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value += static_cast<unsigned char>(theBytes[0]);
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ALOGI("Section %s value is %u [0x%x]\n", name, value, value);
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return value;
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}
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}
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static int readSectionByType(ifstream& elfFile, int type, vector<char>& data) {
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int ret;
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vector<Elf64_Shdr> shTable;
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@ -281,14 +310,36 @@ static bool isRelSection(codeSection& cs, string& name) {
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return false;
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}
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static int readProgDefs(ifstream& elfFile, vector<struct bpf_prog_def>& pd) {
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static int readProgDefs(ifstream& elfFile, vector<struct bpf_prog_def>& pd,
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size_t sizeOfBpfProgDef) {
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vector<char> pdData;
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int ret = readSectionByName("progs", elfFile, pdData);
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// Older file formats do not require a 'progs' section at all.
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// (We should probably figure out whether this is behaviour which is safe to remove now.)
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if (ret == -2) return 0;
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if (ret) return ret;
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pd.resize(pdData.size() / sizeof(struct bpf_prog_def));
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memcpy(pd.data(), pdData.data(), pdData.size());
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if (pdData.size() % sizeOfBpfProgDef) {
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ALOGE("readProgDefs failed due to improper sized progs section, %zu %% %zu != 0\n",
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pdData.size(), sizeOfBpfProgDef);
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return -1;
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};
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int progCount = pdData.size() / sizeOfBpfProgDef;
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pd.resize(progCount);
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size_t trimmedSize = std::min(sizeOfBpfProgDef, sizeof(struct bpf_prog_def));
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const char* dataPtr = pdData.data();
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for (auto& p : pd) {
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// First we zero initialize
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memset(&p, 0, sizeof(p));
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// Then we set non-zero defaults
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p.bpfloader_max_ver = DEFAULT_BPFLOADER_MAX_VER; // v1.0
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// Then we copy over the structure prefix from the ELF file.
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memcpy(&p, dataPtr, trimmedSize);
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// Move to next struct in the ELF file
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dataPtr += sizeOfBpfProgDef;
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}
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return 0;
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}
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@ -335,7 +386,7 @@ static int getSectionSymNames(ifstream& elfFile, const string& sectionName, vect
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}
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/* Read a section by its index - for ex to get sec hdr strtab blob */
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static int readCodeSections(ifstream& elfFile, vector<codeSection>& cs) {
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static int readCodeSections(ifstream& elfFile, vector<codeSection>& cs, size_t sizeOfBpfProgDef) {
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vector<Elf64_Shdr> shTable;
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int entries, ret = 0;
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@ -344,7 +395,7 @@ static int readCodeSections(ifstream& elfFile, vector<codeSection>& cs) {
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entries = shTable.size();
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vector<struct bpf_prog_def> pd;
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ret = readProgDefs(elfFile, pd);
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ret = readProgDefs(elfFile, pd, sizeOfBpfProgDef);
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if (ret) return ret;
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vector<string> progDefNames;
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ret = getSectionSymNames(elfFile, "progs", progDefNames);
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@ -416,7 +467,7 @@ static int getSymNameByIdx(ifstream& elfFile, int index, string& name) {
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}
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static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>& mapFds,
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const char* prefix) {
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const char* prefix, size_t sizeOfBpfMapDef) {
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int ret;
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vector<char> mdData;
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vector<struct bpf_map_def> md;
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@ -426,8 +477,28 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>&
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ret = readSectionByName("maps", elfFile, mdData);
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if (ret == -2) return 0; // no maps to read
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if (ret) return ret;
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md.resize(mdData.size() / sizeof(struct bpf_map_def));
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memcpy(md.data(), mdData.data(), mdData.size());
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if (mdData.size() % sizeOfBpfMapDef) {
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ALOGE("createMaps failed due to improper sized maps section, %zu %% %zu != 0\n",
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mdData.size(), sizeOfBpfMapDef);
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return -1;
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};
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int mapCount = mdData.size() / sizeOfBpfMapDef;
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md.resize(mapCount);
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size_t trimmedSize = std::min(sizeOfBpfMapDef, sizeof(struct bpf_map_def));
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const char* dataPtr = mdData.data();
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for (auto& m : md) {
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// First we zero initialize
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memset(&m, 0, sizeof(m));
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// Then we set non-zero defaults
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m.bpfloader_max_ver = DEFAULT_BPFLOADER_MAX_VER; // v1.0
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// Then we copy over the structure prefix from the ELF file.
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memcpy(&m, dataPtr, trimmedSize);
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// Move to next struct in the ELF file
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dataPtr += sizeOfBpfMapDef;
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}
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ret = getSectionSymNames(elfFile, "maps", mapNames);
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if (ret) return ret;
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@ -436,10 +507,24 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>&
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unique_fd fd;
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int saved_errno;
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// Format of pin location is /sys/fs/bpf/<prefix>map_<filename>_<mapname>
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string mapPinLoc;
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string mapPinLoc =
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string(BPF_FS_PATH) + prefix + "map_" + fname + "_" + string(mapNames[i]);
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bool reuse = false;
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mapPinLoc = string(BPF_FS_PATH) + prefix + "map_" + fname + "_" + string(mapNames[i]);
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if (BPFLOADER_VERSION < md[i].bpfloader_min_ver) {
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ALOGI("skipping map %s which requires bpfloader min ver 0x%05x\n", mapNames[i].c_str(),
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md[i].bpfloader_min_ver);
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mapFds.push_back(std::move(fd)); // -1
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continue;
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}
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if (BPFLOADER_VERSION >= md[i].bpfloader_max_ver) {
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ALOGI("skipping map %s which requires bpfloader max ver 0x%05x\n", mapNames[i].c_str(),
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md[i].bpfloader_max_ver);
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mapFds.push_back(std::move(fd)); // -1
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continue;
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}
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if (access(mapPinLoc.c_str(), F_OK) == 0) {
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fd.reset(bpf_obj_get(mapPinLoc.c_str()));
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saved_errno = errno;
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@ -574,6 +659,8 @@ static int loadCodeSections(const char* elfPath, vector<codeSection>& cs, const
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for (int i = 0; i < (int)cs.size(); i++) {
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string name = cs[i].name;
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unsigned bpfMinVer = DEFAULT_BPFLOADER_MIN_VER; // v0.0
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unsigned bpfMaxVer = DEFAULT_BPFLOADER_MAX_VER; // v1.0
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if (cs[i].prog_def.has_value()) {
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unsigned min_kver = cs[i].prog_def->min_kver;
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@ -582,8 +669,16 @@ static int loadCodeSections(const char* elfPath, vector<codeSection>& cs, const
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max_kver, kvers);
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if (kvers < min_kver) continue;
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if (kvers >= max_kver) continue;
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bpfMinVer = cs[i].prog_def->bpfloader_min_ver;
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bpfMaxVer = cs[i].prog_def->bpfloader_max_ver;
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}
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ALOGD("cs[%d].name:%s requires bpfloader version [0x%05x,0x%05x)\n", i, name.c_str(),
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bpfMinVer, bpfMaxVer);
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if (BPFLOADER_VERSION < bpfMinVer) continue;
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if (BPFLOADER_VERSION >= bpfMaxVer) continue;
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// strip any potential $foo suffix
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// this can be used to provide duplicate programs
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// conditionally loaded based on running kernel version
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@ -674,7 +769,46 @@ int loadProg(const char* elfPath, bool* isCritical, const char* prefix) {
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elfPath, (char*)license.data());
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}
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ret = readCodeSections(elfFile, cs);
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// the following default values are for bpfloader V0.0 format which does not include them
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unsigned int bpfLoaderMinVer =
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readSectionUint("bpfloader_min_ver", elfFile, DEFAULT_BPFLOADER_MIN_VER);
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unsigned int bpfLoaderMaxVer =
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readSectionUint("bpfloader_max_ver", elfFile, DEFAULT_BPFLOADER_MAX_VER);
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size_t sizeOfBpfMapDef =
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readSectionUint("size_of_bpf_map_def", elfFile, DEFAULT_SIZEOF_BPF_MAP_DEF);
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size_t sizeOfBpfProgDef =
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readSectionUint("size_of_bpf_prog_def", elfFile, DEFAULT_SIZEOF_BPF_PROG_DEF);
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// inclusive lower bound check
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if (BPFLOADER_VERSION < bpfLoaderMinVer) {
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ALOGI("BpfLoader version 0x%05x ignoring ELF object %s with min ver 0x%05x\n",
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BPFLOADER_VERSION, elfPath, bpfLoaderMinVer);
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return 0;
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}
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// exclusive upper bound check
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if (BPFLOADER_VERSION >= bpfLoaderMaxVer) {
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ALOGI("BpfLoader version 0x%05x ignoring ELF object %s with max ver 0x%05x\n",
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BPFLOADER_VERSION, elfPath, bpfLoaderMaxVer);
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return 0;
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}
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ALOGI("BpfLoader version 0x%05x processing ELF object %s with ver [0x%05x,0x%05x)\n",
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BPFLOADER_VERSION, elfPath, bpfLoaderMinVer, bpfLoaderMaxVer);
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if (sizeOfBpfMapDef < DEFAULT_SIZEOF_BPF_MAP_DEF) {
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ALOGE("sizeof(bpf_map_def) of %zu is too small (< %d)\n", sizeOfBpfMapDef,
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DEFAULT_SIZEOF_BPF_MAP_DEF);
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return -1;
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}
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if (sizeOfBpfProgDef < DEFAULT_SIZEOF_BPF_PROG_DEF) {
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ALOGE("sizeof(bpf_prog_def) of %zu is too small (< %d)\n", sizeOfBpfProgDef,
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DEFAULT_SIZEOF_BPF_PROG_DEF);
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return -1;
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}
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ret = readCodeSections(elfFile, cs, sizeOfBpfProgDef);
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if (ret) {
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ALOGE("Couldn't read all code sections in %s\n", elfPath);
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return ret;
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@ -683,7 +817,7 @@ int loadProg(const char* elfPath, bool* isCritical, const char* prefix) {
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/* Just for future debugging */
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if (0) dumpAllCs(cs);
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ret = createMaps(elfPath, elfFile, mapFds, prefix);
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ret = createMaps(elfPath, elfFile, mapFds, prefix, sizeOfBpfMapDef);
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if (ret) {
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ALOGE("Failed to create maps: (ret=%d) in %s\n", ret, elfPath);
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return ret;
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@ -6,11 +6,47 @@
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#include "bpf_map_def.h"
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/******************************************************************************
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* WARNING: CHANGES TO THIS FILE OUTSIDE OF AOSP/MASTER ARE LIKELY TO BREAK *
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* DEVICE COMPATIBILITY WITH MAINLINE MODULES SHIPPING EBPF CODE. *
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* *
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* THIS WILL LIKELY RESULT IN BRICKED DEVICES AT SOME ARBITRARY FUTURE TIME *
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* *
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* THAT GOES ESPECIALLY FOR THE 'SEC' 'LICENSE' AND 'CRITICAL' MACRO DEFINES *
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* *
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* We strongly suggest that if you need changes to bpfloader functionality *
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* you get your changes reviewed and accepted into aosp/master. *
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* *
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******************************************************************************/
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/* place things in different elf sections */
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#define SEC(NAME) __attribute__((section(NAME), used))
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/* Example use: LICENSE("GPL"); or LICENSE("Apache 2.0"); */
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#define LICENSE(NAME) char _license[] SEC("license") = (NAME)
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/* Must be present in every program, example usage:
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* LICENSE("GPL"); or LICENSE("Apache 2.0");
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*
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* We also take this opportunity to embed a bunch of other useful values in
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* the resulting .o (This is to enable some limited forward compatibility
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* with mainline module shipped ebpf programs)
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*
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* The bpfloader_{min/max}_ver defines the [min, max) range of bpfloader
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* versions that should load this .o file (bpfloaders outside of this range
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* will simply ignore/skip this *entire* .o)
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* The [inclusive,exclusive) matches what we do for kernel ver dependencies.
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*
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* The size_of_bpf_{map,prog}_def allow the bpfloader to load programs where
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* these structures have been extended with additional fields (they will of
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* course simply be ignored then).
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*
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* If missing, bpfloader_{min/max}_ver default to 0/0x10000 ie. [v0.0, v1.0),
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* while size_of_bpf_{map/prog}_def default to 32/20 which are the v0.0 sizes.
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*/
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#define LICENSE(NAME) \
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unsigned int _bpfloader_min_ver SEC("bpfloader_min_ver") = DEFAULT_BPFLOADER_MIN_VER; \
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unsigned int _bpfloader_max_ver SEC("bpfloader_max_ver") = DEFAULT_BPFLOADER_MAX_VER; \
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size_t _size_of_bpf_map_def SEC("size_of_bpf_map_def") = sizeof(struct bpf_map_def); \
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size_t _size_of_bpf_prog_def SEC("size_of_bpf_prog_def") = sizeof(struct bpf_prog_def); \
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char _license[] SEC("license") = (NAME)
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/* flag the resulting bpf .o file as critical to system functionality,
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* loading all kernel version appropriate programs in it must succeed
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@ -68,6 +104,7 @@ static int (*bpf_map_delete_elem_unsafe)(const struct bpf_map_def* map,
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.key_size = sizeof(TypeOfKey), \
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.value_size = sizeof(TypeOfValue), \
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.max_entries = (num_entries), \
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.map_flags = 0, \
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.uid = (usr), \
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.gid = (grp), \
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.mode = (md), \
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@ -25,6 +25,34 @@
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// Pull in AID_* constants from //system/core/libcutils/include/private/android_filesystem_config.h
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#include <private/android_filesystem_config.h>
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/******************************************************************************
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* *
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* ! ! ! W A R N I N G ! ! ! *
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* *
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* CHANGES TO THESE STRUCTURE DEFINITIONS OUTSIDE OF AOSP/MASTER *WILL* BREAK *
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* MAINLINE MODULE COMPATIBILITY *
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* *
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* AND THUS MAY RESULT IN YOUR DEVICE BRICKING AT SOME ARBITRARY POINT IN *
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* THE FUTURE *
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* *
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* (and even in aosp/master you may only append new fields at the very end, *
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* you may *never* delete fields, change their types, ordering, insert in *
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* the middle, etc. If a mainline module using the old definition has *
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* already shipped (which happens roughly monthly), then it's set in stone) *
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* *
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******************************************************************************/
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// For now we default to v0.0 format
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#ifndef BPFLOADER_VERSION
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#define BPFLOADER_VERSION 0u
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#endif
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// These are the values used if these fields are missing
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#define DEFAULT_BPFLOADER_MIN_VER 0u // v0.0
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#define DEFAULT_BPFLOADER_MAX_VER 0x10000u // v1.0
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#define DEFAULT_SIZEOF_BPF_MAP_DEF 32 // v0.0 struct: enum + alignment padding + 7 uint
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#define DEFAULT_SIZEOF_BPF_PROG_DEF 20 // v0.0 struct: 4 uint + bool + alignment padding
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/*
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* Map structure to be used by Android eBPF C programs. The Android eBPF loader
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* uses this structure from eBPF object to create maps at boot time.
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@ -51,6 +79,12 @@ struct bpf_map_def {
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unsigned int uid; // uid_t
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unsigned int gid; // gid_t
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unsigned int mode; // mode_t
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#if BPFLOADER_VERSION >= 1u
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// The following fields were added in version 0.1
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unsigned int bpfloader_min_ver; // if missing, defaults to 0, ie. v0.0
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unsigned int bpfloader_max_ver; // if missing, defaults to 0x10000, ie. v1.0
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#endif
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};
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struct bpf_prog_def {
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@ -62,4 +96,10 @@ struct bpf_prog_def {
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unsigned int max_kver;
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bool optional; // program section (ie. function) may fail to load, continue onto next func.
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#if BPFLOADER_VERSION >= 1u
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// The following fields were added in version 0.1
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unsigned int bpfloader_min_ver; // if missing, defaults to 0, ie. v0.0
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unsigned int bpfloader_max_ver; // if missing, defaults to 0x10000, ie. v1.0
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#endif
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};
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