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VirtualAlloc on Windows 7 does not currently provide sufficient randomization to protect JIT code from being aligned in large regions at a predictable location.

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This patch manually randomizes the allocation address for PAGE_EXECUTE_READWRITE regions between kAllocationRandomAddressMin and kAllocationRandomAddressMax.

BUG=none
TEST=allocate lots of javascript code and check for contiguous allocations

Patch by Paul Mehta <pmehta@chromium.org>

Review URL: http://codereview.chromium.org/2832095


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5169 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
sgjesse@chromium.org 2010-08-02 15:27:25 +00:00
parent 571eca3118
commit ff00c907cd
2 changed files with 28 additions and 1 deletions
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1
src/platform-linux.cc
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@ -236,6 +236,7 @@ size_t OS::AllocateAlignment() {
void* OS::Allocate(const size_t requested,
size_t* allocated,
bool is_executable) {
// TODO(805): Port randomization of allocated executable memory to Linux.
const size_t msize = RoundUp(requested, sysconf(_SC_PAGESIZE));
int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

28
src/platform-win32.cc
View File

@ -838,12 +838,38 @@ size_t OS::AllocateAlignment() {
void* OS::Allocate(const size_t requested,
size_t* allocated,
bool is_executable) {
// The address range used to randomize RWX allocations in OS::Allocate
// Try not to map pages into the default range that windows loads DLLs
// Note: This does not guarantee RWX regions will be within the
// range kAllocationRandomAddressMin to kAllocationRandomAddressMax
#ifdef V8_HOST_ARCH_64_BIT
static const intptr_t kAllocationRandomAddressMin = 0x0000000080000000;
static const intptr_t kAllocationRandomAddressMax = 0x000004FFFFFFFFFF;
#else
static const intptr_t kAllocationRandomAddressMin = 0x04000000;
static const intptr_t kAllocationRandomAddressMax = 0x4FFFFFFF;
#endif
// VirtualAlloc rounds allocated size to page size automatically.
size_t msize = RoundUp(requested, static_cast<int>(GetPageSize()));
intptr_t address = NULL;
// Windows XP SP2 allows Data Excution Prevention (DEP).
int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
LPVOID mbase = VirtualAlloc(NULL, msize, MEM_COMMIT | MEM_RESERVE, prot);
// For exectutable pages try and randomize the allocation address
if (prot == PAGE_EXECUTE_READWRITE && msize >= Page::kPageSize) {
address = (V8::Random() << kPageSizeBits) | kAllocationRandomAddressMin;
address &= kAllocationRandomAddressMax;
}
LPVOID mbase = VirtualAlloc(reinterpret_cast<void *>(address),
msize,
MEM_COMMIT | MEM_RESERVE,
prot);
if (mbase == NULL && address != NULL)
mbase = VirtualAlloc(NULL, msize, MEM_COMMIT | MEM_RESERVE, prot);
if (mbase == NULL) {
LOG(StringEvent("OS::Allocate", "VirtualAlloc failed"));
return NULL;