// Copyright 2018 The gVisor Authors. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. #include "vdso/vdso_time.h" #include <stdint.h> #include <sys/time.h> #include <time.h> #include "vdso/cycle_clock.h" #include "vdso/seqlock.h" #include "vdso/syscalls.h" // struct params defines the layout of the parameter page maintained by the // kernel (i.e., sentry). // // This is similar to the VVAR page maintained by the normal Linux kernel for // its VDSO, but it has a different layout. // // It must be kept in sync with VDSOParamPage in pkg/sentry/kernel/vdso.go. struct params { uint64_t seq_count; uint64_t monotonic_ready; int64_t monotonic_base_cycles; int64_t monotonic_base_ref; uint64_t monotonic_frequency; uint64_t realtime_ready; int64_t realtime_base_cycles; int64_t realtime_base_ref; uint64_t realtime_frequency; }; // Returns a pointer to the global parameter page. // // This page lives in the page just before the VDSO binary itself. The linker // defines _params as the page before the VDSO. // // Ideally, we'd simply declare _params as an extern struct params. // Unfortunately various combinations of old/new versions of gcc/clang and // gold/bfd struggle to generate references to such a global without generating // relocations. // // So instead, we use inline assembly with a construct that seems to have wide // compatibility across many toolchains. #if __x86_64__ inline struct params* get_params() { struct params* p = nullptr; asm("leaq _params(%%rip), %0" : "=r"(p) : :); return p; } #elif __aarch64__ inline struct params* get_params() { struct params* p = nullptr; asm("adr %0, _params" : "=r"(p) : :); return p; } #else #error "unsupported architecture" #endif namespace vdso { const uint64_t kNsecsPerSec = 1000000000UL; inline struct timespec ns_to_timespec(uint64_t ns) { struct timespec ts; ts.tv_sec = ns / kNsecsPerSec; ts.tv_nsec = ns % kNsecsPerSec; return ts; } inline uint64_t cycles_to_ns(uint64_t frequency, uint64_t cycles) { uint64_t mult = (kNsecsPerSec << 32) / frequency; return ((unsigned __int128)cycles * mult) >> 32; } // ClockRealtime() is the VDSO implementation of clock_gettime(CLOCK_REALTIME). int ClockRealtime(struct timespec* ts) { struct params* params = get_params(); uint64_t seq; uint64_t ready; int64_t base_ref; int64_t base_cycles; uint64_t frequency; int64_t now_cycles; do { seq = read_seqcount_begin(¶ms->seq_count); ready = params->realtime_ready; base_ref = params->realtime_base_ref; base_cycles = params->realtime_base_cycles; frequency = params->realtime_frequency; now_cycles = cycle_clock(); } while (read_seqcount_retry(¶ms->seq_count, seq)); if (!ready) { // The sandbox kernel ensures that we won't compute a time later than this // once the params are ready. return sys_clock_gettime(CLOCK_REALTIME, ts); } int64_t delta_cycles = (now_cycles < base_cycles) ? 0 : now_cycles - base_cycles; int64_t now_ns = base_ref + cycles_to_ns(frequency, delta_cycles); *ts = ns_to_timespec(now_ns); return 0; } // ClockMonotonic() is the VDSO implementation of // clock_gettime(CLOCK_MONOTONIC). int ClockMonotonic(struct timespec* ts) { struct params* params = get_params(); uint64_t seq; uint64_t ready; int64_t base_ref; int64_t base_cycles; uint64_t frequency; int64_t now_cycles; do { seq = read_seqcount_begin(¶ms->seq_count); ready = params->monotonic_ready; base_ref = params->monotonic_base_ref; base_cycles = params->monotonic_base_cycles; frequency = params->monotonic_frequency; now_cycles = cycle_clock(); } while (read_seqcount_retry(¶ms->seq_count, seq)); if (!ready) { // The sandbox kernel ensures that we won't compute a time later than this // once the params are ready. return sys_clock_gettime(CLOCK_MONOTONIC, ts); } int64_t delta_cycles = (now_cycles < base_cycles) ? 0 : now_cycles - base_cycles; int64_t now_ns = base_ref + cycles_to_ns(frequency, delta_cycles); *ts = ns_to_timespec(now_ns); return 0; } } // namespace vdso