2019-04-29 21:25:05 +00:00
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// Copyright 2018 The gVisor Authors.
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2018-04-27 17:37:02 +00:00
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "vdso/vdso_time.h"
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#include <stdint.h>
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#include <sys/time.h>
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#include <time.h>
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#include "vdso/cycle_clock.h"
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#include "vdso/seqlock.h"
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#include "vdso/syscalls.h"
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// struct params defines the layout of the parameter page maintained by the
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// kernel (i.e., sentry).
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//
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// This is similar to the VVAR page maintained by the normal Linux kernel for
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// its VDSO, but it has a different layout.
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//
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// It must be kept in sync with VDSOParamPage in pkg/sentry/kernel/vdso.go.
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struct params {
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uint64_t seq_count;
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uint64_t monotonic_ready;
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int64_t monotonic_base_cycles;
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int64_t monotonic_base_ref;
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uint64_t monotonic_frequency;
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uint64_t realtime_ready;
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int64_t realtime_base_cycles;
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int64_t realtime_base_ref;
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uint64_t realtime_frequency;
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};
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// Returns a pointer to the global parameter page.
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//
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// This page lives in the page just before the VDSO binary itself. The linker
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// defines _params as the page before the VDSO.
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//
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// Ideally, we'd simply declare _params as an extern struct params.
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// Unfortunately various combinations of old/new versions of gcc/clang and
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// gold/bfd struggle to generate references to such a global without generating
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// relocations.
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//
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// So instead, we use inline assembly with a construct that seems to have wide
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// compatibility across many toolchains.
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2019-04-18 23:20:45 +00:00
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#if __x86_64__
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inline struct params* get_params() {
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struct params* p = nullptr;
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asm("leaq _params(%%rip), %0" : "=r"(p) : :);
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return p;
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}
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#elif __aarch64__
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2018-04-27 17:37:02 +00:00
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inline struct params* get_params() {
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struct params* p = nullptr;
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2019-04-18 23:20:45 +00:00
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asm("adr %0, _params" : "=r"(p) : :);
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2018-04-27 17:37:02 +00:00
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return p;
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}
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2019-04-18 23:20:45 +00:00
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#else
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#error "unsupported architecture"
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#endif
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2018-04-27 17:37:02 +00:00
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namespace vdso {
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const uint64_t kNsecsPerSec = 1000000000UL;
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inline struct timespec ns_to_timespec(uint64_t ns) {
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struct timespec ts;
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ts.tv_sec = ns / kNsecsPerSec;
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ts.tv_nsec = ns % kNsecsPerSec;
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return ts;
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}
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inline uint64_t cycles_to_ns(uint64_t frequency, uint64_t cycles) {
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uint64_t mult = (kNsecsPerSec << 32) / frequency;
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return ((unsigned __int128)cycles * mult) >> 32;
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}
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// ClockRealtime() is the VDSO implementation of clock_gettime(CLOCK_REALTIME).
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int ClockRealtime(struct timespec* ts) {
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struct params* params = get_params();
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uint64_t seq;
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uint64_t ready;
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int64_t base_ref;
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int64_t base_cycles;
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uint64_t frequency;
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int64_t now_cycles;
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do {
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seq = read_seqcount_begin(¶ms->seq_count);
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ready = params->realtime_ready;
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base_ref = params->realtime_base_ref;
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base_cycles = params->realtime_base_cycles;
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frequency = params->realtime_frequency;
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now_cycles = cycle_clock();
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} while (read_seqcount_retry(¶ms->seq_count, seq));
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if (!ready) {
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// The sandbox kernel ensures that we won't compute a time later than this
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// once the params are ready.
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return sys_clock_gettime(CLOCK_REALTIME, ts);
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}
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int64_t delta_cycles =
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(now_cycles < base_cycles) ? 0 : now_cycles - base_cycles;
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int64_t now_ns = base_ref + cycles_to_ns(frequency, delta_cycles);
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*ts = ns_to_timespec(now_ns);
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return 0;
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}
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// ClockMonotonic() is the VDSO implementation of
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// clock_gettime(CLOCK_MONOTONIC).
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int ClockMonotonic(struct timespec* ts) {
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struct params* params = get_params();
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uint64_t seq;
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uint64_t ready;
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int64_t base_ref;
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int64_t base_cycles;
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uint64_t frequency;
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int64_t now_cycles;
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do {
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seq = read_seqcount_begin(¶ms->seq_count);
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ready = params->monotonic_ready;
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base_ref = params->monotonic_base_ref;
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base_cycles = params->monotonic_base_cycles;
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frequency = params->monotonic_frequency;
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now_cycles = cycle_clock();
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} while (read_seqcount_retry(¶ms->seq_count, seq));
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if (!ready) {
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// The sandbox kernel ensures that we won't compute a time later than this
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// once the params are ready.
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return sys_clock_gettime(CLOCK_MONOTONIC, ts);
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}
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int64_t delta_cycles =
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(now_cycles < base_cycles) ? 0 : now_cycles - base_cycles;
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int64_t now_ns = base_ref + cycles_to_ns(frequency, delta_cycles);
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*ts = ns_to_timespec(now_ns);
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return 0;
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}
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} // namespace vdso
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