init/security.cpp - android_system_core - Gitiles

 /*
  * Copyright (C) 2017 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 "security.h"
 #include "util.h"

 #include <errno.h>
 #include <fcntl.h>
 #include <linux/perf_event.h>
 #include <selinux/selinux.h>
 #include <sys/ioctl.h>
 #include <sys/syscall.h>
 #include <unistd.h>

 #include <fstream>

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

 using android::base::unique_fd;
 using android::base::SetProperty;

 namespace android {
 namespace init {

 static bool SetHighestAvailableOptionValue(const std::string& path, int min, int max) {
     std::ifstream inf(path, std::fstream::in);
     if (!inf) {
         LOG(ERROR) << "Cannot open for reading: " << path;
         return false;
     }

     int current = max;
     while (current >= min) {
         // try to write out new value
         std::string str_val = std::to_string(current);
         std::ofstream of(path, std::fstream::out);
         if (!of) {
             LOG(ERROR) << "Cannot open for writing: " << path;
             return false;
         }
         of << str_val << std::endl;
         of.close();

         // check to make sure it was recorded
         inf.seekg(0);
         std::string str_rec;
         inf >> str_rec;
         if (str_val.compare(str_rec) == 0) {
             break;
         }
         current--;
     }
     inf.close();

     if (current < min) {
         LOG(ERROR) << "Unable to set minimum option value " << min << " in " << path;
         return false;
     }
     return true;
 }

 #define MMAP_RND_PATH "/proc/sys/vm/mmap_rnd_bits"
 #define MMAP_RND_COMPAT_PATH "/proc/sys/vm/mmap_rnd_compat_bits"

 static bool SetMmapRndBitsMin(int start, int min, bool compat) {
     std::string path;
     if (compat) {
         path = MMAP_RND_COMPAT_PATH;
     } else {
         path = MMAP_RND_PATH;
     }

     return SetHighestAvailableOptionValue(path, min, start);
 }

 // Set /proc/sys/vm/mmap_rnd_bits and potentially
 // /proc/sys/vm/mmap_rnd_compat_bits to the maximum supported values.
 // Returns an error if unable to set these to an acceptable value.
 //
 // To support this sysctl, the following upstream commits are needed:
 //
 // d07e22597d1d mm: mmap: add new /proc tunable for mmap_base ASLR
 // e0c25d958f78 arm: mm: support ARCH_MMAP_RND_BITS
 // 8f0d3aa9de57 arm64: mm: support ARCH_MMAP_RND_BITS
 // 9e08f57d684a x86: mm: support ARCH_MMAP_RND_BITS
 // ec9ee4acd97c drivers: char: random: add get_random_long()
 // 5ef11c35ce86 mm: ASLR: use get_random_long()
 Result<void> SetMmapRndBitsAction(const BuiltinArguments&) {
 // values are arch-dependent
 #if defined(USER_MODE_LINUX)
     // uml does not support mmap_rnd_bits
     return {};
 #elif defined(__aarch64__)
     // arm64 architecture supports 18 - 33 rnd bits depending on pagesize and
     // VA_SIZE. However the kernel might have been compiled with a narrower
     // range using CONFIG_ARCH_MMAP_RND_BITS_MIN/MAX. To use the maximum
     // supported number of bits, we start from the theoretical maximum of 33
     // bits and try smaller values until we reach 24 bits which is the
     // Android-specific minimum. Don't go lower even if the configured maximum
     // is smaller than 24.
     if (SetMmapRndBitsMin(33, 24, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
         return {};
     }
 #elif defined(__riscv)
     // TODO: sv48 and sv57 were both added to the kernel this year, so we
     // probably just need some kernel fixes to enable higher ASLR randomization,
     // but for now 24 is the maximum that the kernel supports.
     if (SetMmapRndBitsMin(24, 18, false)) {
         return {};
     }
 #elif defined(__x86_64__)
     // x86_64 supports 28 - 32 rnd bits, but Android wants to ensure that the
     // theoretical maximum of 32 bits is always supported and used.
     if (SetMmapRndBitsMin(32, 32, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
         return {};
     }
 #elif defined(__arm__) || defined(__i386__)
     // check to see if we're running on 64-bit kernel
     bool h64 = !access(MMAP_RND_COMPAT_PATH, F_OK);
     // supported 32-bit architecture must have 16 bits set
     if (SetMmapRndBitsMin(16, 16, h64)) {
         return {};
     }
 #else
     LOG(ERROR) << "Unknown architecture";
 #endif

     LOG(FATAL) << "Unable to set adequate mmap entropy value!";
     return Error();
 }

 #define KPTR_RESTRICT_PATH "/proc/sys/kernel/kptr_restrict"
 #define KPTR_RESTRICT_MINVALUE 2
 #define KPTR_RESTRICT_MAXVALUE 4

 // Set kptr_restrict to the highest available level.
 //
 // Aborts if unable to set this to an acceptable value.
 Result<void> SetKptrRestrictAction(const BuiltinArguments&) {
     std::string path = KPTR_RESTRICT_PATH;

     if (!SetHighestAvailableOptionValue(path, KPTR_RESTRICT_MINVALUE, KPTR_RESTRICT_MAXVALUE)) {
         LOG(FATAL) << "Unable to set adequate kptr_restrict value!";
         return Error();
     }
     return {};
 }

 // Test for whether the kernel has SELinux hooks for the perf_event_open()
 // syscall. If the hooks are present, we can stop using the other permission
 // mechanism (perf_event_paranoid sysctl), and use only the SELinux policy to
 // control access to the syscall. The hooks are expected on all Android R
 // release kernels, but might be absent on devices that upgrade while keeping an
 // older kernel.
 //
 // There is no direct/synchronous way of finding out that a syscall failed due
 // to SELinux. Therefore we test for a combination of a success and a failure
 // that are explained by the platform's SELinux policy for the "init" domain:
 // * cpu-scoped perf_event is allowed
 // * ioctl() on the event fd is disallowed with EACCES
 //
 // Since init has CAP_SYS_ADMIN, these tests are not affected by the system-wide
 // perf_event_paranoid sysctl.
 //
 // If the SELinux hooks are detected, a special sysprop
 // (sys.init.perf_lsm_hooks) is set, which translates to a modification of
 // perf_event_paranoid (through init.rc sysprop actions).
 //
 // TODO(b/137092007): this entire test can be removed once the platform stops
 // supporting kernels that precede the perf_event_open hooks (Android common
 // kernels 4.4 and 4.9).
 Result<void> TestPerfEventSelinuxAction(const BuiltinArguments&) {
     // Special case: for *development devices* that boot with permissive
     // SELinux, treat the LSM hooks as present for the effect of lowering the
     // perf_event_paranoid sysctl. The sysprop is reused for pragmatic reasons,
     // as there no existing way for init rules to check for permissive boot at
     // the time of writing.
     if (ALLOW_PERMISSIVE_SELINUX) {
         if (!security_getenforce()) {
             LOG(INFO) << "Permissive SELinux boot, forcing sys.init.perf_lsm_hooks to 1.";
             SetProperty("sys.init.perf_lsm_hooks", "1");
             return {};
         }
     }

     // Use a trivial event that will be configured, but not started.
     struct perf_event_attr pe = {
             .type = PERF_TYPE_SOFTWARE,
             .size = sizeof(struct perf_event_attr),
             .config = PERF_COUNT_SW_TASK_CLOCK,
             .disabled = 1,
             .exclude_kernel = 1,
     };

     // Open the above event targeting cpu 0. (EINTR not possible.)
     unique_fd fd(static_cast<int>(syscall(__NR_perf_event_open, &pe, /*pid=*/-1,
                                           /*cpu=*/0,
                                           /*group_fd=*/-1, /*flags=*/0)));
     if (fd == -1) {
         PLOG(ERROR) << "Unexpected perf_event_open error";
         return {};
     }

     int ioctl_ret = ioctl(fd.get(), PERF_EVENT_IOC_RESET);
     if (ioctl_ret != -1) {
         // Success implies that the kernel doesn't have the hooks.
         return {};
     } else if (errno != EACCES) {
         PLOG(ERROR) << "Unexpected perf_event ioctl error";
         return {};
     }

     // Conclude that the SELinux hooks are present.
     SetProperty("sys.init.perf_lsm_hooks", "1");
     return {};
 }

 }  // namespace init
 }  // namespace android
	/*
	* Copyright (C) 2017 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 "security.h"
	#include "util.h"

	#include <errno.h>
	#include <fcntl.h>
	#include <linux/perf_event.h>
	#include <selinux/selinux.h>
	#include <sys/ioctl.h>
	#include <sys/syscall.h>
	#include <unistd.h>

	#include <fstream>

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

	using android::base::unique_fd;
	using android::base::SetProperty;

	namespace android {
	namespace init {

	static bool SetHighestAvailableOptionValue(const std::string& path, int min, int max) {
	std::ifstream inf(path, std::fstream::in);
	if (!inf) {
	LOG(ERROR) << "Cannot open for reading: " << path;
	return false;
	}

	int current = max;
	while (current >= min) {
	// try to write out new value
	std::string str_val = std::to_string(current);
	std::ofstream of(path, std::fstream::out);
	if (!of) {
	LOG(ERROR) << "Cannot open for writing: " << path;
	return false;
	}
	of << str_val << std::endl;
	of.close();

	// check to make sure it was recorded
	inf.seekg(0);
	std::string str_rec;
	inf >> str_rec;
	if (str_val.compare(str_rec) == 0) {
	break;
	}
	current--;
	}
	inf.close();

	if (current < min) {
	LOG(ERROR) << "Unable to set minimum option value " << min << " in " << path;
	return false;
	}
	return true;
	}

	#define MMAP_RND_PATH "/proc/sys/vm/mmap_rnd_bits"
	#define MMAP_RND_COMPAT_PATH "/proc/sys/vm/mmap_rnd_compat_bits"

	static bool SetMmapRndBitsMin(int start, int min, bool compat) {
	std::string path;
	if (compat) {
	path = MMAP_RND_COMPAT_PATH;
	} else {
	path = MMAP_RND_PATH;
	}

	return SetHighestAvailableOptionValue(path, min, start);
	}

	// Set /proc/sys/vm/mmap_rnd_bits and potentially
	// /proc/sys/vm/mmap_rnd_compat_bits to the maximum supported values.
	// Returns an error if unable to set these to an acceptable value.
	//
	// To support this sysctl, the following upstream commits are needed:
	//
	// d07e22597d1d mm: mmap: add new /proc tunable for mmap_base ASLR
	// e0c25d958f78 arm: mm: support ARCH_MMAP_RND_BITS
	// 8f0d3aa9de57 arm64: mm: support ARCH_MMAP_RND_BITS
	// 9e08f57d684a x86: mm: support ARCH_MMAP_RND_BITS
	// ec9ee4acd97c drivers: char: random: add get_random_long()
	// 5ef11c35ce86 mm: ASLR: use get_random_long()
	Result<void> SetMmapRndBitsAction(const BuiltinArguments&) {
	// values are arch-dependent
	#if defined(USER_MODE_LINUX)
	// uml does not support mmap_rnd_bits
	return {};
	#elif defined(__aarch64__)
	// arm64 architecture supports 18 - 33 rnd bits depending on pagesize and
	// VA_SIZE. However the kernel might have been compiled with a narrower
	// range using CONFIG_ARCH_MMAP_RND_BITS_MIN/MAX. To use the maximum
	// supported number of bits, we start from the theoretical maximum of 33
	// bits and try smaller values until we reach 24 bits which is the
	// Android-specific minimum. Don't go lower even if the configured maximum
	// is smaller than 24.
	if (SetMmapRndBitsMin(33, 24, false) && (!Has32BitAbi() \|\| SetMmapRndBitsMin(16, 16, true))) {
	return {};
	}
	#elif defined(__riscv)
	// TODO: sv48 and sv57 were both added to the kernel this year, so we
	// probably just need some kernel fixes to enable higher ASLR randomization,
	// but for now 24 is the maximum that the kernel supports.
	if (SetMmapRndBitsMin(24, 18, false)) {
	return {};
	}
	#elif defined(__x86_64__)
	// x86_64 supports 28 - 32 rnd bits, but Android wants to ensure that the
	// theoretical maximum of 32 bits is always supported and used.
	if (SetMmapRndBitsMin(32, 32, false) && (!Has32BitAbi() \|\| SetMmapRndBitsMin(16, 16, true))) {
	return {};
	}
	#elif defined(__arm__) \|\| defined(__i386__)
	// check to see if we're running on 64-bit kernel
	bool h64 = !access(MMAP_RND_COMPAT_PATH, F_OK);
	// supported 32-bit architecture must have 16 bits set
	if (SetMmapRndBitsMin(16, 16, h64)) {
	return {};
	}
	#else
	LOG(ERROR) << "Unknown architecture";
	#endif

	LOG(FATAL) << "Unable to set adequate mmap entropy value!";
	return Error();
	}

	#define KPTR_RESTRICT_PATH "/proc/sys/kernel/kptr_restrict"
	#define KPTR_RESTRICT_MINVALUE 2
	#define KPTR_RESTRICT_MAXVALUE 4

	// Set kptr_restrict to the highest available level.
	//
	// Aborts if unable to set this to an acceptable value.
	Result<void> SetKptrRestrictAction(const BuiltinArguments&) {
	std::string path = KPTR_RESTRICT_PATH;

	if (!SetHighestAvailableOptionValue(path, KPTR_RESTRICT_MINVALUE, KPTR_RESTRICT_MAXVALUE)) {
	LOG(FATAL) << "Unable to set adequate kptr_restrict value!";
	return Error();
	}
	return {};
	}

	// Test for whether the kernel has SELinux hooks for the perf_event_open()
	// syscall. If the hooks are present, we can stop using the other permission
	// mechanism (perf_event_paranoid sysctl), and use only the SELinux policy to
	// control access to the syscall. The hooks are expected on all Android R
	// release kernels, but might be absent on devices that upgrade while keeping an
	// older kernel.
	//
	// There is no direct/synchronous way of finding out that a syscall failed due
	// to SELinux. Therefore we test for a combination of a success and a failure
	// that are explained by the platform's SELinux policy for the "init" domain:
	// * cpu-scoped perf_event is allowed
	// * ioctl() on the event fd is disallowed with EACCES
	//
	// Since init has CAP_SYS_ADMIN, these tests are not affected by the system-wide
	// perf_event_paranoid sysctl.
	//
	// If the SELinux hooks are detected, a special sysprop
	// (sys.init.perf_lsm_hooks) is set, which translates to a modification of
	// perf_event_paranoid (through init.rc sysprop actions).
	//
	// TODO(b/137092007): this entire test can be removed once the platform stops
	// supporting kernels that precede the perf_event_open hooks (Android common
	// kernels 4.4 and 4.9).
	Result<void> TestPerfEventSelinuxAction(const BuiltinArguments&) {
	// Special case: for development devices that boot with permissive
	// SELinux, treat the LSM hooks as present for the effect of lowering the
	// perf_event_paranoid sysctl. The sysprop is reused for pragmatic reasons,
	// as there no existing way for init rules to check for permissive boot at
	// the time of writing.
	if (ALLOW_PERMISSIVE_SELINUX) {
	if (!security_getenforce()) {
	LOG(INFO) << "Permissive SELinux boot, forcing sys.init.perf_lsm_hooks to 1.";
	SetProperty("sys.init.perf_lsm_hooks", "1");
	return {};
	}
	}

	// Use a trivial event that will be configured, but not started.
	struct perf_event_attr pe = {
	.type = PERF_TYPE_SOFTWARE,
	.size = sizeof(struct perf_event_attr),
	.config = PERF_COUNT_SW_TASK_CLOCK,
	.disabled = 1,
	.exclude_kernel = 1,
	};

	// Open the above event targeting cpu 0. (EINTR not possible.)
	unique_fd fd(static_cast<int>(syscall(__NR_perf_event_open, &pe, /pid=/-1,
	/cpu=/0,
	/group_fd=/-1, /flags=/0)));
	if (fd == -1) {
	PLOG(ERROR) << "Unexpected perf_event_open error";
	return {};
	}

	int ioctl_ret = ioctl(fd.get(), PERF_EVENT_IOC_RESET);
	if (ioctl_ret != -1) {
	// Success implies that the kernel doesn't have the hooks.
	return {};
	} else if (errno != EACCES) {
	PLOG(ERROR) << "Unexpected perf_event ioctl error";
	return {};
	}

	// Conclude that the SELinux hooks are present.
	SetProperty("sys.init.perf_lsm_hooks", "1");
	return {};
	}

	} // namespace init
	} // namespace android