Add support for memfd

This patch adds support to make libcutils create and use memfd where
possible, instead of ashmem.

The libcutils library is made dynamic, since apps are still sending over
ashmem FDs to processes and we are working on moving those apps away
from ashmem. The best we can do for that is make the library work, and
force apps in the long run to move away from directly using ashmem.

Due to further complications mentioned in the 'NOTE' section of the
patch, memfd is kept disabled for now, so nothing changes yet. To enable
it, set the sys.use_memfd property (check user_debug build).

Bug: 113362644
Change-Id: I491cb7841b664db5b1c26b3e07a440a14810e182
Signed-off-by: Joel Fernandes <joelaf@google.com>

libcutils/Android.bp

@@ -172,7 +172,10 @@ cc_library {
         }
     },
 
-    shared_libs: ["liblog"],
+    shared_libs: [
+        "liblog",
+        "libbase",
+    ],
     header_libs: [
         "libbase_headers",
         "libcutils_headers",

libcutils/ashmem-dev.cpp

@@ -29,17 +29,34 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/ashmem.h>
+#include <linux/memfd.h>
+#include <log/log.h>
 #include <pthread.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <sys/stat.h>
+#include <sys/syscall.h>
 #include <sys/sysmacros.h>
 #include <sys/types.h>
 #include <unistd.h>
-#include <log/log.h>
+
+#include <android-base/properties.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
+
+/*
+ * The minimum vendor API level at and after which it is safe to use memfd.
+ * This is to facilitate deprecation of ashmem.
+ */
+#define MIN_MEMFD_VENDOR_API_LEVEL 29
+#define MIN_MEMFD_VENDOR_API_LEVEL_CHAR 'Q'
+
 /* ashmem identity */
 static dev_t __ashmem_rdev;
 /*
@@ -72,6 +89,130 @@ openFdType initOpenAshmemFd() {
 }
 #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
+ * check for needed support in it. Also we check if the VNDK version of
+ * libcutils being used is new enough, if its not, then we cannot use memfd
+ * since the older copies may be using ashmem so we just use ashmem. Once all
+ * Android devices that are getting updates are new enough (ex, they were
+ * originally shipped with Android release > P), then we can just use memfd and
+ * delete all ashmem code from libcutils (while preserving the interface).
+ *
+ * NOTE:
+ * The sys.use_memfd property is set by default to false in Android
+ * to temporarily disable memfd, till vendor and apps are ready for it.
+ * The main issue: either apps or vendor processes can directly make ashmem
+ * IOCTLs on FDs they receive by assuming they are ashmem, without going
+ * through libcutils. Such fds could have very well be originally created with
+ * libcutils hence they could be memfd. Thus the IOCTLs will break.
+ *
+ * Set default value of sys.use_memfd property to true once the issue is
+ * resolved, so that the code can then self-detect if kernel support is present
+ * on the device. The property can also set to true from adb shell, for
+ * debugging.
+ */
+
+static bool debug_log = false;            /* set to true for verbose logging and other debug  */
+static bool pin_deprecation_warn = true; /* Log the pin deprecation warning only once */
+
+/* Determine if vendor processes would be ok with memfd in the system:
+ *
+ * If VNDK is using older libcutils, don't use memfd. This is so that the
+ * same shared memory mechanism is used across binder transactions between
+ * vendor partition processes and system partition processes.
+ */
+static bool check_vendor_memfd_allowed() {
+    std::string vndk_version = android::base::GetProperty("ro.vndk.version", "");
+
+    if (vndk_version == "") {
+        ALOGE("memfd: ro.vndk.version not defined or invalid (%s), this is mandated since P.\n",
+              vndk_version.c_str());
+        return false;
+    }
+
+    /* No issues if vendor is targetting current Dessert */
+    if (vndk_version == "current") {
+        return false;
+    }
+
+    /* Check if VNDK version is a number and act on it */
+    char* p;
+    long int vers = strtol(vndk_version.c_str(), &p, 10);
+    if (*p == 0) {
+        if (vers < MIN_MEMFD_VENDOR_API_LEVEL) {
+            ALOGI("memfd: device VNDK version (%s) is < Q so using ashmem.\n",
+                  vndk_version.c_str());
+            return false;
+        }
+
+        return true;
+    }
+
+    /* If its not a number, assume string, but check if its a sane string */
+    if (tolower(vndk_version[0]) < 'a' || tolower(vndk_version[0]) > 'z') {
+        ALOGE("memfd: ro.vndk.version not defined or invalid (%s), this is mandated since P.\n",
+              vndk_version.c_str());
+        return false;
+    }
+
+    if (tolower(vndk_version[0]) < tolower(MIN_MEMFD_VENDOR_API_LEVEL_CHAR)) {
+        ALOGI("memfd: device is using VNDK version (%s) which is less than Q. Use ashmem only.\n",
+              vndk_version.c_str());
+        return false;
+    }
+
+    return true;
+}
+
+
+/* Determine if memfd can be supported. This is just one-time hardwork
+ * which will be cached by the caller.
+ */
+static bool __has_memfd_support() {
+    if (check_vendor_memfd_allowed() == false) {
+        return false;
+    }
+
+    /* Used to turn on/off the detection at runtime, in the future this
+     * property will be removed once we switch everything over to ashmem.
+     * Currently it is used only for debugging to switch the system over.
+     */
+    if (!android::base::GetBoolProperty("sys.use_memfd", false)) {
+        if (debug_log) {
+            ALOGD("sys.use_memfd=false so memfd disabled\n");
+        }
+        return false;
+    }
+
+    /* Check if kernel support exists, otherwise fall back to ashmem */
+    android::base::unique_fd fd(
+            syscall(__NR_memfd_create, "test_android_memfd", MFD_ALLOW_SEALING));
+    if (fd == -1) {
+        ALOGE("memfd_create failed: %s, no memfd support.\n", strerror(errno));
+        return false;
+    }
+
+    if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
+        ALOGE("fcntl(F_ADD_SEALS) failed: %s, no memfd support.\n", strerror(errno));
+        return false;
+    }
+
+    if (debug_log) {
+        ALOGD("memfd: device has memfd support, using it\n");
+    }
+    return true;
+}
+
+static bool has_memfd_support() {
+    /* memfd_supported is the initial global per-process state of what is known
+     * about memfd.
+     */
+    static bool memfd_supported = __has_memfd_support();
+
+    return memfd_supported;
+}
+
 /* logistics of getting file descriptor for ashmem */
 static int __ashmem_open_locked()
 {
@@ -177,11 +318,49 @@ static int __ashmem_check_failure(int fd, int result)
     return result;
 }
 
+static bool memfd_is_ashmem(int fd) {
+    static bool fd_check_error_once = false;
+
+    if (__ashmem_is_ashmem(fd, 0) == 0) {
+        if (!fd_check_error_once) {
+            ALOGE("memfd: memfd expected but ashmem fd used - please use libcutils.\n");
+            fd_check_error_once = true;
+        }
+
+        return true;
+    }
+
+    return false;
+}
+
 int ashmem_valid(int fd)
 {
+    if (has_memfd_support() && !memfd_is_ashmem(fd)) {
+        return 1;
+    }
+
     return __ashmem_is_ashmem(fd, 0) >= 0;
 }
 
+static int memfd_create_region(const char* name, size_t size) {
+    android::base::unique_fd fd(syscall(__NR_memfd_create, name, MFD_ALLOW_SEALING));
+
+    if (fd == -1) {
+        ALOGE("memfd_create(%s, %zd) failed: %s\n", name, size, strerror(errno));
+        return -1;
+    }
+
+    if (ftruncate(fd, size) == -1) {
+        ALOGE("ftruncate(%s, %zd) failed for memfd creation: %s\n", name, size, strerror(errno));
+        return -1;
+    }
+
+    if (debug_log) {
+        ALOGE("memfd_create(%s, %zd) success. fd=%d\n", name, size, fd.get());
+    }
+    return fd.release();
+}
+
 /*
  * ashmem_create_region - creates a new ashmem region and returns the file
  * descriptor, or <0 on error
@@ -193,6 +372,10 @@ int ashmem_create_region(const char *name, size_t size)
 {
     int ret, save_errno;
 
+    if (has_memfd_support()) {
+        return memfd_create_region(name ? name : "none", size);
+    }
+
     int fd = __ashmem_open();
     if (fd < 0) {
         return fd;
@@ -222,28 +405,78 @@ error:
     return ret;
 }
 
+static int memfd_set_prot_region(int fd, int prot) {
+    /* Only proceed if an fd needs to be write-protected */
+    if (prot & PROT_WRITE) {
+        return 0;
+    }
+
+    if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
+        ALOGE("memfd_set_prot_region(%d, %d): F_SEAL_FUTURE_WRITE seal failed: %s\n", fd, prot,
+              strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
 int ashmem_set_prot_region(int fd, int prot)
 {
+    if (has_memfd_support() && !memfd_is_ashmem(fd)) {
+        return memfd_set_prot_region(fd, prot);
+    }
+
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_SET_PROT_MASK, prot)));
 }
 
 int ashmem_pin_region(int fd, size_t offset, size_t len)
 {
+    if (!pin_deprecation_warn || debug_log) {
+        ALOGE("Pinning is deprecated since Android Q. Please use trim or other methods.\n");
+        pin_deprecation_warn = true;
+    }
+
+    if (has_memfd_support() && !memfd_is_ashmem(fd)) {
+        return 0;
+    }
+
     // TODO: should LP64 reject too-large offset/len?
     ashmem_pin pin = { static_cast<uint32_t>(offset), static_cast<uint32_t>(len) };
-
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_PIN, &pin)));
 }
 
 int ashmem_unpin_region(int fd, size_t offset, size_t len)
 {
+    if (!pin_deprecation_warn || debug_log) {
+        ALOGE("Pinning is deprecated since Android Q. Please use trim or other methods.\n");
+        pin_deprecation_warn = true;
+    }
+
+    if (has_memfd_support() && !memfd_is_ashmem(fd)) {
+        return 0;
+    }
+
     // TODO: should LP64 reject too-large offset/len?
     ashmem_pin pin = { static_cast<uint32_t>(offset), static_cast<uint32_t>(len) };
-
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_UNPIN, &pin)));
 }
 
 int ashmem_get_size_region(int fd)
 {
+    if (has_memfd_support() && !memfd_is_ashmem(fd)) {
+        struct stat sb;
+
+        if (fstat(fd, &sb) == -1) {
+            ALOGE("ashmem_get_size_region(%d): fstat failed: %s\n", fd, strerror(errno));
+            return -1;
+        }
+
+        if (debug_log) {
+            ALOGD("ashmem_get_size_region(%d): %d\n", fd, static_cast<int>(sb.st_size));
+        }
+
+        return sb.st_size;
+    }
+
     return __ashmem_check_failure(fd, TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_GET_SIZE, NULL)));
 }

libpixelflinger/tests/Android.bp

@@ -8,6 +8,7 @@ cc_defaults {
 
     header_libs: ["libpixelflinger_internal"],
     static_libs: [
+        "libbase",
         "libcutils",
         "liblog",
         "libpixelflinger",