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Commit 92fd3caf authored by Tri Vo's avatar Tri Vo
Browse files

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
parent ff89b8d8

libcutils/ashmem-dev.cpp

+19 −50
Original line number Diff line number Diff line
@@ -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

+0 −2
Original line number Diff line number Diff line
@@ -94,5 +94,3 @@ int ashmem_get_size_region(int fd) 


    return buf.st_size;

}
 


void ashmem_init() {}

libcutils/include/cutils/ashmem.h

+0 −1
Original line number Diff line number Diff line
@@ -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

}