tequilaOS/platform_system_core
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Let the kernel hwrng thread manage hw_random mixing.

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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
This commit is contained in:
Elliott Hughes 2021-02-05 11:10:00 -08:00
parent 3ce24b87a2
commit eedd38a82a
3 changed files with 0 additions and 59 deletions
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5
init/init.cpp
View file

@ -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") {

53
init/security.cpp
View file

@ -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) {

1
init/security.h
View file

@ -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&);