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// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "gin/thread_isolation.h"
#if PA_BUILDFLAG(ENABLE_THREAD_ISOLATION)
#include <sys/mman.h>
#include <sys/utsname.h>
#include <cstddef>
#include "base/check.h"
#include "base/check_op.h"
#include "base/compiler_specific.h"
#include "base/memory/page_size.h"
#include "base/metrics/histogram_functions.h"
#include "base/no_destructor.h"
#include "partition_alloc/thread_isolation/alignment.h"
WEAK_SYMBOL extern int pkey_alloc(unsigned int flags,
unsigned int access_rights);
namespace {
bool KernelHasPkruFix() {
// PKU was broken on Linux kernels before 5.13 (see
// https://lore.kernel.org/all/20210623121456.399107624@linutronix.de/).
// A fix is also included in the 5.4.182 and 5.10.103 versions ("x86/fpu:
// Correct pkru/xstate inconsistency" by Brian Geffon <bgeffon@google.com>).
// Thus check the kernel version we are running on, and bail out if does not
// contain the fix.
struct utsname uname_buffer;
CHECK_EQ(0, uname(&uname_buffer));
int kernel, major, minor;
// Conservatively return if the release does not match the format we expect.
// SAFETY: required from system when uname() returns successfully.
if (UNSAFE_BUFFERS(sscanf(uname_buffer.release, "%d.%d.%d", &kernel, &major,
&minor)) != 3) {
return -1;
}
return kernel > 5 || (kernel == 5 && major >= 13) || // anything >= 5.13
(kernel == 5 && major == 4 && minor >= 182) || // 5.4 >= 5.4.182
(kernel == 5 && major == 10 && minor >= 103); // 5.10 >= 5.10.103
}
int PkeyAlloc(int access_rights) {
if (!pkey_alloc) {
return -1;
}
static bool kernel_has_pkru_fix = KernelHasPkruFix();
if (!kernel_has_pkru_fix) {
return -1;
}
return pkey_alloc(0, access_rights);
}
uint32_t Rdpkru() {
uint32_t pkru;
asm volatile(".byte 0x0f,0x01,0xee\n" : "=a"(pkru) : "c"(0), "d"(0));
return pkru;
}
void Wrpkru(uint32_t pkru) {
asm volatile(".byte 0x0f,0x01,0xef\n" : : "a"(pkru), "c"(0), "d"(0));
}
static constexpr uint32_t kBitsPerPkey = 2;
void PkeyDisableWriteAccess(int pkey) {
#ifdef PKEY_DISABLE_WRITE
uint32_t pkru = Rdpkru();
uint32_t disable_write = static_cast<uint32_t>(PKEY_DISABLE_WRITE)
<< (static_cast<uint32_t>(pkey) * kBitsPerPkey);
Wrpkru(pkru | disable_write);
#endif
}
} // namespace
namespace gin {
void ThreadIsolationData::InitializeBeforeThreadCreation() {
bool page_size_mismatch = PA_THREAD_ISOLATED_ALIGN_SZ < base::GetPageSize();
base::UmaHistogramBoolean("V8.CFIPageSizeMismatch", page_size_mismatch);
if (page_size_mismatch) {
// We write-protect global variables and need to align and pad them to (a
// multiple of) the OS page size. But since page size is not a compile time
// constant, check at runtime that our value was large enough.
return;
}
pkey = PkeyAlloc(0);
if (pkey == -1) {
return;
}
allocator->Initialize(pkey);
PkeyDisableWriteAccess(pkey);
}
bool ThreadIsolationData::Initialized() const {
return pkey != -1;
}
ThreadIsolationData& GetThreadIsolationData() {
static ThreadIsolationData thread_isolation_data;
DCHECK_EQ((reinterpret_cast<size_t>(&thread_isolation_data) %
PA_THREAD_ISOLATED_ALIGN_SZ),
0llu);
return thread_isolation_data;
}
} // namespace gin
#endif // PA_BUILDFLAG(ENABLE_THREAD_ISOLATION)
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