libcutils: route to /dev/ashmem<boot_id> instead of ashmemd

Having libcutils ask ashmemd for ashmem fds results in unsatisfactory
performance/memory overhead. Introduce a duplicate of /dev/ashmem and
route to it instead.

Our goal remains as before, namely, use SELinux to phase out usage of
ashmem that doesn't go through libcutils.

Bug: 139855428
Test: boot aosp_crosshatch, browse internet, use camera
Change-Id: I02260a9042acb412571b11f1f4c1d8608483064a

libcutils/ashmem-dev.cpp

@@ -23,9 +23,6 @@
  */
 #define LOG_TAG "ashmem"
 
-#ifndef __ANDROID_VNDK__
-#include <dlfcn.h>
-#endif
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/ashmem.h>
@@ -42,11 +39,11 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#include <android-base/file.h>
 #include <android-base/properties.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 
-#define ASHMEM_DEVICE "/dev/ashmem"
-
 /* Will be added to UAPI once upstream change is merged */
 #define F_SEAL_FUTURE_WRITE 0x0010
 
@@ -65,32 +62,6 @@ static dev_t __ashmem_rdev;
  */
 static pthread_mutex_t __ashmem_lock = PTHREAD_MUTEX_INITIALIZER;
 
-/*
- * We use ashmemd to enforce that apps don't open /dev/ashmem directly. Vendor
- * code can't access system aidl services per Treble requirements. So we limit
- * ashmemd access to the system variant of libcutils.
- */
-#ifndef __ANDROID_VNDK__
-using openFdType = int (*)();
-
-static openFdType openFd;
-
-openFdType initOpenAshmemFd() {
-    openFdType openFd = nullptr;
-    void* handle = dlopen("libashmemd_client.so", RTLD_NOW);
-    if (!handle) {
-        ALOGE("Failed to dlopen() libashmemd_client.so: %s", dlerror());
-        return openFd;
-    }
-
-    openFd = reinterpret_cast<openFdType>(dlsym(handle, "openAshmemdFd"));
-    if (!openFd) {
-        ALOGE("Failed to dlsym() openAshmemdFd() function: %s", dlerror());
-    }
-    return openFd;
-}
-#endif
-
 /*
  * has_memfd_support() determines if the device can use memfd. memfd support
  * has been there for long time, but certain things in it may be missing.  We
@@ -215,25 +186,31 @@ static bool has_memfd_support() {
     return memfd_supported;
 }
 
+static std::string get_ashmem_device_path() {
+    static const std::string boot_id_path = "/proc/sys/kernel/random/boot_id";
+    std::string boot_id;
+    if (!android::base::ReadFileToString(boot_id_path, &boot_id)) {
+        ALOGE("Failed to read %s: %s.\n", boot_id_path.c_str(), strerror(errno));
+        return "";
+    };
+    boot_id = android::base::Trim(boot_id);
+
+    return "/dev/ashmem" + boot_id;
+}
+
 /* logistics of getting file descriptor for ashmem */
 static int __ashmem_open_locked()
 {
+    static const std::string ashmem_device_path = get_ashmem_device_path();
+
     int ret;
     struct stat st;
 
-    int fd = -1;
-#ifndef __ANDROID_VNDK__
-    if (!openFd) {
-        openFd = initOpenAshmemFd();
+    if (ashmem_device_path.empty()) {
+        return -1;
     }
 
-    if (openFd) {
-        fd = openFd();
-    }
-#endif
-    if (fd < 0) {
-        fd = TEMP_FAILURE_RETRY(open(ASHMEM_DEVICE, O_RDWR | O_CLOEXEC));
-    }
+    int fd = TEMP_FAILURE_RETRY(open(ashmem_device_path.c_str(), O_RDWR | O_CLOEXEC));
     if (fd < 0) {
         return fd;
     }
@@ -485,11 +462,3 @@ int ashmem_get_size_region(int fd)
 
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_GET_SIZE, NULL)));
 }
-
-void ashmem_init() {
-#ifndef __ANDROID_VNDK__
-    pthread_mutex_lock(&__ashmem_lock);
-    openFd = initOpenAshmemFd();
-    pthread_mutex_unlock(&__ashmem_lock);
-#endif  //__ANDROID_VNDK__
-}

libcutils/ashmem-host.cpp

@@ -94,5 +94,3 @@ int ashmem_get_size_region(int fd)
 
     return buf.st_size;
 }
-
-void ashmem_init() {}

libcutils/include/cutils/ashmem.h

@@ -26,7 +26,6 @@ int ashmem_set_prot_region(int fd, int prot);
 int ashmem_pin_region(int fd, size_t offset, size_t len);
 int ashmem_unpin_region(int fd, size_t offset, size_t len);
 int ashmem_get_size_region(int fd);
-void ashmem_init();
 
 #ifdef __cplusplus
 }