simpleperf/kallsyms.cpp - platform/system/extras - Git at Google

 /*
  * Copyright (C) 2020 The Android Open Source Project
  *
  * 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 "kallsyms.h"

 #include <inttypes.h>

 #include <string>

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>

 #include "environment.h"
 #include "read_elf.h"
 #include "utils.h"

 namespace simpleperf {

 #if defined(__linux__)

 namespace {

 const char kKallsymsPath[] = "/proc/kallsyms";
 const char kProcModulesPath[] = "/proc/modules";
 const char kPtrRestrictPath[] = "/proc/sys/kernel/kptr_restrict";
 const char kLowerPtrRestrictAndroidProp[] = "security.lower_kptr_restrict";
 const unsigned int kMinLineTestNonNullSymbols = 10;

 // Tries to read the kernel symbol file and ensure that at least some symbol
 // addresses are non-null.
 bool CanReadKernelSymbolAddresses() {
   LineReader reader(kKallsymsPath);
   if (!reader.Ok()) {
     LOG(DEBUG) << "Failed to read " << kKallsymsPath;
     return false;
   }
   auto symbol_callback = [&](const KernelSymbol& symbol) { return (symbol.addr != 0u); };
   for (unsigned int i = 0; i < kMinLineTestNonNullSymbols; i++) {
     std::string* line = reader.ReadLine();
     if (line == nullptr) {
       return false;
     }
     if (ProcessKernelSymbols(*line, symbol_callback)) {
       return true;
     }
   }
   return false;
 }

 // Define a scope in which access to kallsyms is possible.
 // This is based on the Perfetto implementation.
 class ScopedKptrUnrestrict {
  public:
   ScopedKptrUnrestrict();   // Lowers kptr_restrict if necessary.
   ~ScopedKptrUnrestrict();  // Restores the initial kptr_restrict.

   // Indicates if access to kallsyms should be successful.
   bool KallsymsAvailable() { return kallsyms_available_; }

   static void ResetWarning() { kernel_address_warning_printed_ = false; }

  private:
   bool WriteKptrRestrict(const std::string& value);
   void PrintWarning();

   bool restore_property_ = false;
   bool restore_restrict_value_ = false;
   std::string saved_restrict_value_;
   bool kallsyms_available_ = false;

   static bool kernel_address_warning_printed_;
 };

 bool ScopedKptrUnrestrict::kernel_address_warning_printed_ = false;

 ScopedKptrUnrestrict::ScopedKptrUnrestrict() {
   if (CanReadKernelSymbolAddresses()) {
     // Everything seems to work (e.g., we are running as root and kptr_restrict
     // is < 2). Don't touching anything.
     kallsyms_available_ = true;
     return;
   }

   if (GetAndroidVersion() >= 12 && IsRoot()) {
     // Enable kernel addresses by setting property.
     if (!android::base::SetProperty(kLowerPtrRestrictAndroidProp, "1")) {
       LOG(DEBUG) << "Unable to set " << kLowerPtrRestrictAndroidProp << " to 1.";
       PrintWarning();
       return;
     }
     restore_property_ = true;
     // Init takes some time to react to the property change.
     // Unfortunately, we cannot read kptr_restrict because of SELinux. Instead,
     // we detect this by reading the initial lines of kallsyms and checking
     // that they are non-zero. This loop waits for at most 250ms (50 * 5ms).
     for (int attempt = 1; attempt <= 50; ++attempt) {
       usleep(5000);
       if (CanReadKernelSymbolAddresses()) {
         kallsyms_available_ = true;
         return;
       }
     }
     LOG(DEBUG) << "kallsyms addresses are still masked after setting "
                << kLowerPtrRestrictAndroidProp;
     PrintWarning();
     return;
   }

   // Otherwise, read the kptr_restrict value and lower it if needed.
   if (!android::base::ReadFileToString(kPtrRestrictPath, &saved_restrict_value_)) {
     LOG(DEBUG) << "Failed to read " << kPtrRestrictPath;
     PrintWarning();
     return;
   }

   // Progressively lower kptr_restrict until we can read kallsyms.
   for (int value = atoi(saved_restrict_value_.c_str()); value > 0; --value) {
     if (!WriteKptrRestrict(std::to_string(value))) {
       break;
     }
     restore_restrict_value_ = true;
     if (CanReadKernelSymbolAddresses()) {
       kallsyms_available_ = true;
       return;
     }
   }
   PrintWarning();
 }

 ScopedKptrUnrestrict::~ScopedKptrUnrestrict() {
   if (restore_property_) {
     android::base::SetProperty(kLowerPtrRestrictAndroidProp, "0");
   }
   if (restore_restrict_value_) {
     WriteKptrRestrict(saved_restrict_value_);
   }
 }

 bool ScopedKptrUnrestrict::WriteKptrRestrict(const std::string& value) {
   if (!android::base::WriteStringToFile(value, kPtrRestrictPath)) {
     LOG(DEBUG) << "Failed to set " << kPtrRestrictPath << " to " << value;
     return false;
   }
   return true;
 }

 void ScopedKptrUnrestrict::PrintWarning() {
   if (!kernel_address_warning_printed_) {
     kernel_address_warning_printed_ = true;
     LOG(WARNING) << "Access to kernel symbol addresses is restricted. If "
                  << "possible, please do `echo 0 >/proc/sys/kernel/kptr_restrict` "
                  << "to fix this.";
   }
 }

 }  // namespace

 std::vector<KernelMmap> GetLoadedModules() {
   ScopedKptrUnrestrict kptr_unrestrict;
   if (!kptr_unrestrict.KallsymsAvailable()) return {};
   std::vector<KernelMmap> result;
   LineReader reader(kProcModulesPath);
   if (!reader.Ok()) {
     // There is no /proc/modules on Android devices, so we don't print error if failed to open it.
     PLOG(DEBUG) << "failed to open file /proc/modules";
     return result;
   }
   std::string* line;
   std::string name_buf;
   while ((line = reader.ReadLine()) != nullptr) {
     // Parse line like: nf_defrag_ipv6 34768 1 nf_conntrack_ipv6, Live 0xffffffffa0fe5000
     name_buf.resize(line->size());
     char* name = name_buf.data();
     uint64_t addr;
     uint64_t len;
     if (sscanf(line->data(), "%s%" PRIu64 "%*u%*s%*s 0x%" PRIx64, name, &len, &addr) == 3) {
       KernelMmap map;
       map.name = name;
       map.start_addr = addr;
       map.len = len;
       result.push_back(map);
     }
   }
   bool all_zero = true;
   for (const auto& map : result) {
     if (map.start_addr != 0) {
       all_zero = false;
     }
   }
   if (all_zero) {
     LOG(DEBUG) << "addresses in /proc/modules are all zero, so ignore kernel modules";
     return std::vector<KernelMmap>();
   }
   return result;
 }

 uint64_t GetKernelStartAddress() {
   ScopedKptrUnrestrict kptr_unrestrict;
   if (!kptr_unrestrict.KallsymsAvailable()) return 0;
   LineReader reader(kKallsymsPath);
   if (!reader.Ok()) {
     return 0;
   }
   std::string* line;
   while ((line = reader.ReadLine()) != nullptr) {
     if (strstr(line->data(), "_stext") != nullptr) {
       uint64_t addr;
       if (sscanf(line->data(), "%" PRIx64, &addr) == 1) {
         return addr;
       }
     }
   }
   return 0;
 }

 bool LoadKernelSymbols(std::string* kallsyms) {
   ScopedKptrUnrestrict kptr_unrestrict;
   if (kptr_unrestrict.KallsymsAvailable()) {
     return android::base::ReadFileToString(kKallsymsPath, kallsyms);
   }
   return false;
 }

 void ResetKernelAddressWarning() {
   ScopedKptrUnrestrict::ResetWarning();
 }

 #endif  // defined(__linux__)

 bool ProcessKernelSymbols(std::string& symbol_data,
                           const std::function<bool(const KernelSymbol&)>& callback) {
   char* p = &symbol_data[0];
   char* data_end = p + symbol_data.size();
   while (p < data_end) {
     char* line_end = strchr(p, '\n');
     if (line_end != nullptr) {
       *line_end = '\0';
     }
     size_t line_size = (line_end != nullptr) ? (line_end - p) : (data_end - p);
     // Parse line like: ffffffffa005c4e4 d __warned.41698       [libsas]
     char name[line_size];
     char module[line_size];
     strcpy(module, "");

     KernelSymbol symbol;
     int ret = sscanf(p, "%" PRIx64 " %c %s%s", &symbol.addr, &symbol.type, name, module);
     if (line_end != nullptr) {
       *line_end = '\n';
       p = line_end + 1;
     } else {
       p = data_end;
     }
     if (ret >= 3) {
       if (IsArmMappingSymbol(name)) {
         continue;
       }

       symbol.name = name;
       size_t module_len = strlen(module);
       if (module_len > 2 && module[0] == '[' && module[module_len - 1] == ']') {
         module[module_len - 1] = '\0';
         symbol.module = &module[1];
       } else {
         symbol.module = nullptr;
       }

       if (callback(symbol)) {
         return true;
       }
     }
   }
   return false;
 }

 }  // namespace simpleperf
	/*
	* Copyright (C) 2020 The Android Open Source Project
	*
	* 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 "kallsyms.h"

	#include <inttypes.h>

	#include <string>

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>

	#include "environment.h"
	#include "read_elf.h"
	#include "utils.h"

	namespace simpleperf {

	#if defined(__linux__)

	namespace {

	const char kKallsymsPath[] = "/proc/kallsyms";
	const char kProcModulesPath[] = "/proc/modules";
	const char kPtrRestrictPath[] = "/proc/sys/kernel/kptr_restrict";
	const char kLowerPtrRestrictAndroidProp[] = "security.lower_kptr_restrict";
	const unsigned int kMinLineTestNonNullSymbols = 10;

	// Tries to read the kernel symbol file and ensure that at least some symbol
	// addresses are non-null.
	bool CanReadKernelSymbolAddresses() {
	LineReader reader(kKallsymsPath);
	if (!reader.Ok()) {
	LOG(DEBUG) << "Failed to read " << kKallsymsPath;
	return false;
	}
	auto symbol_callback = [&](const KernelSymbol& symbol) { return (symbol.addr != 0u); };
	for (unsigned int i = 0; i < kMinLineTestNonNullSymbols; i++) {
	std::string* line = reader.ReadLine();
	if (line == nullptr) {
	return false;
	}
	if (ProcessKernelSymbols(*line, symbol_callback)) {
	return true;
	}
	}
	return false;
	}

	// Define a scope in which access to kallsyms is possible.
	// This is based on the Perfetto implementation.
	class ScopedKptrUnrestrict {
	public:
	ScopedKptrUnrestrict(); // Lowers kptr_restrict if necessary.
	~ScopedKptrUnrestrict(); // Restores the initial kptr_restrict.

	// Indicates if access to kallsyms should be successful.
	bool KallsymsAvailable() { return kallsyms_available_; }

	static void ResetWarning() { kernel_address_warning_printed_ = false; }

	private:
	bool WriteKptrRestrict(const std::string& value);
	void PrintWarning();

	bool restore_property_ = false;
	bool restore_restrict_value_ = false;
	std::string saved_restrict_value_;
	bool kallsyms_available_ = false;

	static bool kernel_address_warning_printed_;
	};

	bool ScopedKptrUnrestrict::kernel_address_warning_printed_ = false;

	ScopedKptrUnrestrict::ScopedKptrUnrestrict() {
	if (CanReadKernelSymbolAddresses()) {
	// Everything seems to work (e.g., we are running as root and kptr_restrict
	// is < 2). Don't touching anything.
	kallsyms_available_ = true;
	return;
	}

	if (GetAndroidVersion() >= 12 && IsRoot()) {
	// Enable kernel addresses by setting property.
	if (!android::base::SetProperty(kLowerPtrRestrictAndroidProp, "1")) {
	LOG(DEBUG) << "Unable to set " << kLowerPtrRestrictAndroidProp << " to 1.";
	PrintWarning();
	return;
	}
	restore_property_ = true;
	// Init takes some time to react to the property change.
	// Unfortunately, we cannot read kptr_restrict because of SELinux. Instead,
	// we detect this by reading the initial lines of kallsyms and checking
	// that they are non-zero. This loop waits for at most 250ms (50 * 5ms).
	for (int attempt = 1; attempt <= 50; ++attempt) {
	usleep(5000);
	if (CanReadKernelSymbolAddresses()) {
	kallsyms_available_ = true;
	return;
	}
	}
	LOG(DEBUG) << "kallsyms addresses are still masked after setting "
	<< kLowerPtrRestrictAndroidProp;
	PrintWarning();
	return;
	}

	// Otherwise, read the kptr_restrict value and lower it if needed.
	if (!android::base::ReadFileToString(kPtrRestrictPath, &saved_restrict_value_)) {
	LOG(DEBUG) << "Failed to read " << kPtrRestrictPath;
	PrintWarning();
	return;
	}

	// Progressively lower kptr_restrict until we can read kallsyms.
	for (int value = atoi(saved_restrict_value_.c_str()); value > 0; --value) {
	if (!WriteKptrRestrict(std::to_string(value))) {
	break;
	}
	restore_restrict_value_ = true;
	if (CanReadKernelSymbolAddresses()) {
	kallsyms_available_ = true;
	return;
	}
	}
	PrintWarning();
	}

	ScopedKptrUnrestrict::~ScopedKptrUnrestrict() {
	if (restore_property_) {
	android::base::SetProperty(kLowerPtrRestrictAndroidProp, "0");
	}
	if (restore_restrict_value_) {
	WriteKptrRestrict(saved_restrict_value_);
	}
	}

	bool ScopedKptrUnrestrict::WriteKptrRestrict(const std::string& value) {
	if (!android::base::WriteStringToFile(value, kPtrRestrictPath)) {
	LOG(DEBUG) << "Failed to set " << kPtrRestrictPath << " to " << value;
	return false;
	}
	return true;
	}

	void ScopedKptrUnrestrict::PrintWarning() {
	if (!kernel_address_warning_printed_) {
	kernel_address_warning_printed_ = true;
	LOG(WARNING) << "Access to kernel symbol addresses is restricted. If "
	<< "possible, please do `echo 0 >/proc/sys/kernel/kptr_restrict` "
	<< "to fix this.";
	}
	}

	} // namespace

	std::vector<KernelMmap> GetLoadedModules() {
	ScopedKptrUnrestrict kptr_unrestrict;
	if (!kptr_unrestrict.KallsymsAvailable()) return {};
	std::vector<KernelMmap> result;
	LineReader reader(kProcModulesPath);
	if (!reader.Ok()) {
	// There is no /proc/modules on Android devices, so we don't print error if failed to open it.
	PLOG(DEBUG) << "failed to open file /proc/modules";
	return result;
	}
	std::string* line;
	std::string name_buf;
	while ((line = reader.ReadLine()) != nullptr) {
	// Parse line like: nf_defrag_ipv6 34768 1 nf_conntrack_ipv6, Live 0xffffffffa0fe5000
	name_buf.resize(line->size());
	char* name = name_buf.data();
	uint64_t addr;
	uint64_t len;
	if (sscanf(line->data(), "%s%" PRIu64 "%u%s%*s 0x%" PRIx64, name, &len, &addr) == 3) {
	KernelMmap map;
	map.name = name;
	map.start_addr = addr;
	map.len = len;
	result.push_back(map);
	}
	}
	bool all_zero = true;
	for (const auto& map : result) {
	if (map.start_addr != 0) {
	all_zero = false;
	}
	}
	if (all_zero) {
	LOG(DEBUG) << "addresses in /proc/modules are all zero, so ignore kernel modules";
	return std::vector<KernelMmap>();
	}
	return result;
	}

	uint64_t GetKernelStartAddress() {
	ScopedKptrUnrestrict kptr_unrestrict;
	if (!kptr_unrestrict.KallsymsAvailable()) return 0;
	LineReader reader(kKallsymsPath);
	if (!reader.Ok()) {
	return 0;
	}
	std::string* line;
	while ((line = reader.ReadLine()) != nullptr) {
	if (strstr(line->data(), "_stext") != nullptr) {
	uint64_t addr;
	if (sscanf(line->data(), "%" PRIx64, &addr) == 1) {
	return addr;
	}
	}
	}
	return 0;
	}

	bool LoadKernelSymbols(std::string* kallsyms) {
	ScopedKptrUnrestrict kptr_unrestrict;
	if (kptr_unrestrict.KallsymsAvailable()) {
	return android::base::ReadFileToString(kKallsymsPath, kallsyms);
	}
	return false;
	}

	void ResetKernelAddressWarning() {
	ScopedKptrUnrestrict::ResetWarning();
	}

	#endif // defined(__linux__)

	bool ProcessKernelSymbols(std::string& symbol_data,
	const std::function<bool(const KernelSymbol&)>& callback) {
	char* p = &symbol_data[0];
	char* data_end = p + symbol_data.size();
	while (p < data_end) {
	char* line_end = strchr(p, '\n');
	if (line_end != nullptr) {
	*line_end = '\0';
	}
	size_t line_size = (line_end != nullptr) ? (line_end - p) : (data_end - p);
	// Parse line like: ffffffffa005c4e4 d __warned.41698 [libsas]
	char name[line_size];
	char module[line_size];
	strcpy(module, "");

	KernelSymbol symbol;
	int ret = sscanf(p, "%" PRIx64 " %c %s%s", &symbol.addr, &symbol.type, name, module);
	if (line_end != nullptr) {
	*line_end = '\n';
	p = line_end + 1;
	} else {
	p = data_end;
	}
	if (ret >= 3) {
	if (IsArmMappingSymbol(name)) {
	continue;
	}

	symbol.name = name;
	size_t module_len = strlen(module);
	if (module_len > 2 && module[0] == '[' && module[module_len - 1] == ']') {
	module[module_len - 1] = '\0';
	symbol.module = &module[1];
	} else {
	symbol.module = nullptr;
	}

	if (callback(symbol)) {
	return true;
	}
	}
	}
	return false;
	}

	} // namespace simpleperf