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Commit bfe6900f authored by Ricardo Quesada's avatar Ricardo Quesada
Browse files

fs-verity: replace ioctl(FS_IOC_MEASURE_VERITY) with statx() 

This CL replaces the open(file) + ioctl(FS_IOC_MEASURE_VERITY) with
statx() to improve performance. This is because opening fs-verity files
is expensive.

This CL assumes that statx(STATX_ATTR_VERITY) is supported by the kernel.
This is the case for all the Android common kernels that support
fs-verity.

Bug: 146676114
Test: atest com.android.apkverity.ApkVerityTest
      All 17 tests passed
      Tested on Cuttlefish.
Change-Id: I21c70132682c0d4ae6922419b269aa9f5de2fb72
parent bac0268f

services/core/java/com/android/server/security/VerityUtils.java

+6 −10
Original line number Diff line number Diff line
@@ -81,22 +81,18 @@ abstract public class VerityUtils { 


    /** Returns whether the file has fs-verity enabled. */

    public static boolean hasFsverity(@NonNull String filePath) {

        // NB: only measure but not check the actual measurement here. As long as this succeeds,

        // the file is on readable if the measurement can be verified against a trusted key, and

        // this is good enough for installed apps.

        int errno = measureFsverityNative(filePath);

        if (errno != 0) {

            if (errno != OsConstants.ENODATA) {

                Slog.e(TAG, "Failed to measure fs-verity, errno " + errno + ": " + filePath);

            }

        int retval = statxForFsverityNative(filePath);

        if (retval < 0) {

            Slog.e(TAG, "Failed to check whether fs-verity is enabled, errno " + -retval + ": "

                    + filePath);

            return false;

        }

        return true;

        return (retval == 1);

    }



    private static native int enableFsverityNative(@NonNull String filePath,

            @NonNull byte[] pkcs7Signature);

    private static native int measureFsverityNative(@NonNull String filePath);

    private static native int statxForFsverityNative(@NonNull String filePath);



    /**

     * Generates legacy Merkle tree and fs-verity metadata with Signing Block skipped.

services/core/jni/com_android_server_security_VerityUtils.cpp

+17 −22
Original line number Diff line number Diff line
@@ -25,17 +25,14 @@ 
#include <errno.h>

#include <fcntl.h>

#include <linux/fsverity.h>

#include <linux/stat.h>

#include <string.h>

#include <sys/ioctl.h>

#include <sys/stat.h>

#include <sys/types.h>



#include <type_traits>



#include <android-base/unique_fd.h>



const int kSha256Bytes = 32;



namespace android {



namespace {
@@ -69,30 +66,28 @@ int enableFsverity(JNIEnv* env, jobject /* clazz */, jstring filePath, jbyteArra 
    return 0;

}



int measureFsverity(JNIEnv* env, jobject /* clazz */, jstring filePath) {

    using Storage = std::aligned_storage_t<sizeof(fsverity_digest) + kSha256Bytes>;



    Storage bytes;

    fsverity_digest *data = reinterpret_cast<fsverity_digest *>(&bytes);

    data->digest_size = kSha256Bytes;  // the only input/output parameter



// Returns whether the file has fs-verity enabled.

// 0 if it is not present, 1 if is present, and -errno if there was an error.

int statxForFsverity(JNIEnv *env, jobject /* clazz */, jstring filePath) {

    ScopedUtfChars path(env, filePath);

    if (path.c_str() == nullptr) {

        return EINVAL;

    }

    ::android::base::unique_fd rfd(open(path.c_str(), O_RDONLY | O_CLOEXEC));

    if (rfd.get() < 0) {

        return errno;



    struct statx out = {};

    if (statx(AT_FDCWD, path.c_str(), 0 /* flags */, STATX_ALL, &out) != 0) {

        return -errno;

    }

    if (ioctl(rfd.get(), FS_IOC_MEASURE_VERITY, data) < 0) {

        return errno;



    // Sanity check.

    if ((out.stx_attributes_mask & STATX_ATTR_VERITY) == 0) {

        ALOGE("Unexpected, STATX_ATTR_VERITY not supported by kernel");

        return -ENOSYS;

    }

    return 0;



    return (out.stx_attributes & STATX_ATTR_VERITY) != 0;

}



const JNINativeMethod sMethods[] = {

        {"enableFsverityNative", "(Ljava/lang/String;[B)I", (void *)enableFsverity},

    { "measureFsverityNative", "(Ljava/lang/String;)I", (void *)measureFsverity },

        {"statxForFsverityNative", "(Ljava/lang/String;)I", (void *)statxForFsverity},

};



}  // namespace