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Commit eedd38a8 authored by Elliott Hughes's avatar Elliott Hughes
Browse files

Let the kernel hwrng thread manage hw_random mixing. 

This has been something the kernel does automatically since 2014, so
there's no obvious reason to add extra work during boot to duplicate
that effort.

Bug: http://b/179086242
Test: treehugger
Change-Id: I44cce99a892e4f2a6a303c2126bd29f955f5fb23
parent 3ce24b87

init/init.cpp

+0 −5
Original line number Diff line number Diff line
@@ -902,7 +902,6 @@ int SecondStageMain(int argc, char** argv) { 
    am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");

    am.QueueBuiltinAction(TransitionSnapuserdAction, "TransitionSnapuserd");

    // ... so that we can start queuing up actions that require stuff from /dev.

    am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");

    am.QueueBuiltinAction(SetMmapRndBitsAction, "SetMmapRndBits");

    Keychords keychords;

    am.QueueBuiltinAction(
@@ -918,10 +917,6 @@ int SecondStageMain(int argc, char** argv) { 
    // Trigger all the boot actions to get us started.

    am.QueueEventTrigger("init");



    // Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random

    // wasn't ready immediately after wait_for_coldboot_done

    am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");



    // Don't mount filesystems or start core system services in charger mode.

    std::string bootmode = GetProperty("ro.bootmode", "");

    if (bootmode == "charger") {

init/security.cpp

+0 −53
Original line number Diff line number Diff line
@@ -36,59 +36,6 @@ using android::base::SetProperty; 
namespace android {

namespace init {



// Writes 512 bytes of output from Hardware RNG (/dev/hw_random, backed

// by Linux kernel's hw_random framework) into Linux RNG's via /dev/urandom.

// Does nothing if Hardware RNG is not present.

//

// Since we don't yet trust the quality of Hardware RNG, these bytes are not

// mixed into the primary pool of Linux RNG and the entropy estimate is left

// unmodified.

//

// If the HW RNG device /dev/hw_random is present, we require that at least

// 512 bytes read from it are written into Linux RNG. QA is expected to catch

// devices/configurations where these I/O operations are blocking for a long

// time. We do not reboot or halt on failures, as this is a best-effort

// attempt.

Result<void> MixHwrngIntoLinuxRngAction(const BuiltinArguments&) {

    unique_fd hwrandom_fd(

        TEMP_FAILURE_RETRY(open("/dev/hw_random", O_RDONLY | O_NOFOLLOW | O_CLOEXEC)));

    if (hwrandom_fd == -1) {

        if (errno == ENOENT) {

            LOG(INFO) << "/dev/hw_random not found";

            // It's not an error to not have a Hardware RNG.

            return {};

        }

        return ErrnoError() << "Failed to open /dev/hw_random";

    }



    unique_fd urandom_fd(

        TEMP_FAILURE_RETRY(open("/dev/urandom", O_WRONLY | O_NOFOLLOW | O_CLOEXEC)));

    if (urandom_fd == -1) {

        return ErrnoError() << "Failed to open /dev/urandom";

    }



    char buf[512];

    size_t total_bytes_written = 0;

    while (total_bytes_written < sizeof(buf)) {

        ssize_t chunk_size =

            TEMP_FAILURE_RETRY(read(hwrandom_fd, buf, sizeof(buf) - total_bytes_written));

        if (chunk_size == -1) {

            return ErrnoError() << "Failed to read from /dev/hw_random";

        } else if (chunk_size == 0) {

            return Error() << "Failed to read from /dev/hw_random: EOF";

        }



        chunk_size = TEMP_FAILURE_RETRY(write(urandom_fd, buf, chunk_size));

        if (chunk_size == -1) {

            return ErrnoError() << "Failed to write to /dev/urandom";

        }

        total_bytes_written += chunk_size;

    }



    LOG(INFO) << "Mixed " << total_bytes_written << " bytes from /dev/hw_random into /dev/urandom";

    return {};

}



static bool SetHighestAvailableOptionValue(const std::string& path, int min, int max) {

    std::ifstream inf(path, std::fstream::in);

    if (!inf) {

init/security.h

+0 −1
Original line number Diff line number Diff line
@@ -26,7 +26,6 @@ 
namespace android {

namespace init {



Result<void> MixHwrngIntoLinuxRngAction(const BuiltinArguments&);

Result<void> SetMmapRndBitsAction(const BuiltinArguments&);

Result<void> SetKptrRestrictAction(const BuiltinArguments&);

Result<void> TestPerfEventSelinuxAction(const BuiltinArguments&);