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/*
* Copyright (C) 2020 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if defined(LIBC_STATIC)
#error This file should not be compiled for static targets.
#endif
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ucontext.h>
#include <sys/un.h>
#include <async_safe/log.h>
#include <platform/bionic/malloc.h>
#include <platform/bionic/reserved_signals.h>
#include <private/ErrnoRestorer.h>
#include <private/ScopedFd.h>
#include "malloc_heapprofd.h"
// This file defines the handler for the reserved signal sent by the Android
// platform's profilers. The accompanying signal value discriminates between
// specific requestors:
// 0: heapprofd heap profiler.
// 1: traced_perf perf profiler.
static constexpr int kHeapprofdSignalValue = 0;
static constexpr int kTracedPerfSignalValue = 1;
static void HandleProfilingSignal(int, siginfo_t*, void*);
// Called during dynamic libc preinit.
__LIBC_HIDDEN__ void __libc_init_profiling_handlers() {
struct sigaction action = {};
action.sa_flags = SA_SIGINFO | SA_RESTART;
action.sa_sigaction = HandleProfilingSignal;
sigaction(BIONIC_SIGNAL_PROFILER, &action, nullptr);
// The perfetto_hprof ART plugin installs a signal handler to handle this signal. That plugin
// does not get loaded for a) non-apps, b) non-profilable apps on user. The default signal
// disposition is to crash. We do not want the target to crash if we accidentally target a
// non-app or non-profilable process.
signal(BIONIC_SIGNAL_ART_PROFILER, SIG_IGN);
}
static void HandleSigsysSeccompOverride(int, siginfo_t*, void*);
static void HandleTracedPerfSignal();
static void HandleProfilingSignal(int /*signal_number*/, siginfo_t* info, void* /*ucontext*/) {
ErrnoRestorer errno_restorer;
if (info->si_code != SI_QUEUE) {
return;
}
int signal_value = info->si_value.sival_int;
async_safe_format_log(ANDROID_LOG_INFO, "libc", "%s: received profiling signal with si_value: %d",
getprogname(), signal_value);
// Proceed only if the process is considered profileable.
bool profileable = false;
android_mallopt(M_GET_PROCESS_PROFILEABLE, &profileable, sizeof(profileable));
if (!profileable) {
async_safe_write_log(ANDROID_LOG_ERROR, "libc", "profiling signal rejected (not profileable)");
return;
}
// Temporarily override SIGSYS handling, in a best-effort attempt at not
// crashing if we happen to be running in a process with a seccomp filter that
// disallows some of the syscalls done by this signal handler. This protects
// against SECCOMP_RET_TRAP with a crashing SIGSYS handler (typical of android
// minijails). Won't help if the filter is using SECCOMP_RET_KILL_*.
// Note: the override is process-wide, but short-lived. The syscalls are still
// blocked, but the overridden handler recovers from SIGSYS, and fakes the
// syscall return value as ENOSYS.
struct sigaction sigsys_override = {};
sigsys_override.sa_sigaction = &HandleSigsysSeccompOverride;
sigsys_override.sa_flags = SA_SIGINFO;
struct sigaction old_act = {};
sigaction(SIGSYS, &sigsys_override, &old_act);
if (signal_value == kHeapprofdSignalValue) {
HandleHeapprofdSignal();
} else if (signal_value == kTracedPerfSignalValue) {
HandleTracedPerfSignal();
} else {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "unrecognized profiling signal si_value: %d",
signal_value);
}
sigaction(SIGSYS, &old_act, nullptr);
}
// Open /proc/self/{maps,mem}, connect to traced_perf, send the fds over the
// socket. Everything happens synchronously within the signal handler. Socket
// is made non-blocking, and we do not retry.
static void HandleTracedPerfSignal() {
ScopedFd sock_fd{ socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0 /*protocol*/) };
if (sock_fd.get() == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to create socket: %s", strerror(errno));
return;
}
sockaddr_un saddr{ AF_UNIX, "/dev/socket/traced_perf" };
size_t addrlen = sizeof(sockaddr_un);
if (connect(sock_fd.get(), reinterpret_cast<const struct sockaddr*>(&saddr), addrlen) == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to connect to traced_perf socket: %s",
strerror(errno));
return;
}
// If the process is undumpable, /proc/self/mem will be owned by root:root, and therefore
// inaccessible to the process itself (see man 5 proc). We temporarily mark the process as
// dumpable to allow for the open. Note: prctl is not async signal safe per posix, but bionic's
// implementation is. Error checking on prctls is omitted due to them being trivial.
int orig_dumpable = prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
if (!orig_dumpable) {
prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
}
ScopedFd maps_fd{ open("/proc/self/maps", O_RDONLY | O_CLOEXEC) };
ScopedFd mem_fd{ open("/proc/self/mem", O_RDONLY | O_CLOEXEC) };
if (!orig_dumpable) {
prctl(PR_SET_DUMPABLE, orig_dumpable, 0, 0, 0);
}
if (maps_fd.get() == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to open /proc/self/maps: %s",
strerror(errno));
return;
}
if (mem_fd.get() == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to open /proc/self/mem: %s",
strerror(errno));
return;
}
// Send 1 byte with auxiliary data carrying two fds.
int send_fds[2] = { maps_fd.get(), mem_fd.get() };
int num_fds = 2;
char iobuf[1] = {};
msghdr msg_hdr = {};
iovec iov = { reinterpret_cast<void*>(iobuf), sizeof(iobuf) };
msg_hdr.msg_iov = &iov;
msg_hdr.msg_iovlen = 1;
alignas(cmsghdr) char control_buf[256] = {};
const auto raw_ctl_data_sz = num_fds * sizeof(int);
const size_t control_buf_len = static_cast<size_t>(CMSG_SPACE(raw_ctl_data_sz));
msg_hdr.msg_control = control_buf;
msg_hdr.msg_controllen = control_buf_len; // used by CMSG_FIRSTHDR
struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg_hdr);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = static_cast<size_t>(CMSG_LEN(raw_ctl_data_sz));
memcpy(CMSG_DATA(cmsg), send_fds, num_fds * sizeof(int));
if (sendmsg(sock_fd.get(), &msg_hdr, 0) == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to sendmsg: %s", strerror(errno));
}
}
static void HandleSigsysSeccompOverride(int /*signal_number*/, siginfo_t* info,
void* void_context) {
ErrnoRestorer errno_restorer;
if (info->si_code != SYS_SECCOMP) {
return;
}
async_safe_format_log(
ANDROID_LOG_WARN, "libc",
"Profiling setup: trapped seccomp SIGSYS for syscall %d. Returning ENOSYS to caller.",
info->si_syscall);
// The handler is responsible for setting the return value as if the system
// call happened (which is arch-specific). Use a plausible unsuccessful value.
auto ret = -ENOSYS;
ucontext_t* ctx = reinterpret_cast<ucontext_t*>(void_context);
#if defined(__arm__)
ctx->uc_mcontext.arm_r0 = ret;
#elif defined(__aarch64__)
ctx->uc_mcontext.regs[0] = ret; // x0
#elif defined(__i386__)
ctx->uc_mcontext.gregs[REG_EAX] = ret;
#elif defined(__x86_64__)
ctx->uc_mcontext.gregs[REG_RAX] = ret;
#else
#error "unsupported architecture"
#endif
}
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