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[fuchsia] Always allocate executable memory in W^X mode

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In W^X mode (i.e., FLAG_write_protect_code), the Dart VM allocates
code memory with is_executable==false and then later makes it
executable with Protect(kReadExecute). However, on Fuchsia, this will
require a VMO with ZX_RIGHT_EXECUTE (which soon will not be the
default).

This CL takes the approach of always adding ZX_RIGHT_EXECUTE when in
W^X mode. This is suboptimal because it means all VM allocated memory
can be changed to executable, but currently the OS-independent
VirtualMemory::Allocate API doesn't provide us a way to identify
memory that doesn't need to be executable now but will in the future.
(Note that ZX_RIGHT_EXECUTE only *allows* mapping the memory as
executable; the memory is still initially mapped by
VirtualMemory::Allocate as non-executable.)

Extending the VirtualMemory::Allocate API is tracked in FL-172.

Bug: SEC-42
Change-Id: I20555c546c5ab1798c4c36b7394f6221d3993c9e
Reviewed-on: https://dart-review.googlesource.com/c/90882
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Zach Anderson <zra@google.com>
This commit is contained in:
Matthew Dempsky 2019-01-24 16:59:08 +00:00 committed by commit-bot@chromium.org
parent c9b1877cbf
commit 8e2f3ea4d6
1 changed files with 17 additions and 4 deletions
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21
runtime/vm/virtual_memory_fuchsia.cc
View file

@ -35,6 +35,8 @@
namespace dart {
DECLARE_FLAG(bool, write_protect_code);
uword VirtualMemory::page_size_ = 0;
void VirtualMemory::Init() {
@ -44,6 +46,14 @@ void VirtualMemory::Init() {
VirtualMemory* VirtualMemory::Allocate(intptr_t size,
bool is_executable,
const char* name) {
// When FLAG_write_protect_code is active, the VM allocates code
// memory with !is_executable, and later changes to executable via
// VirtualMemory::Protect, which requires ZX_RIGHT_EXECUTE on the
// underlying VMO. Conservatively assume all memory needs to be
// executable in this mode.
// TODO(mdempsky): Make into parameter.
const bool can_prot_exec = FLAG_write_protect_code;
ASSERT(Utils::IsAligned(size, page_size_));
zx_handle_t vmo = ZX_HANDLE_INVALID;
zx_status_t status = zx_vmo_create(size, 0u, &vmo);
@ -57,8 +67,8 @@ VirtualMemory* VirtualMemory::Allocate(intptr_t size,
zx_object_set_property(vmo, ZX_PROP_NAME, name, strlen(name));
}
if (is_executable) {
// Add ZX_PERM_EXECUTE permission to VMO, so it can be mapped
if (is_executable || can_prot_exec) {
// Add ZX_RIGHT_EXECUTE permission to VMO, so it can be mapped
// into memory as executable.
status = zx_vmo_replace_as_executable(vmo, ZX_HANDLE_INVALID, &vmo);
if (status != ZX_OK) {
@ -88,6 +98,9 @@ VirtualMemory* VirtualMemory::AllocateAligned(intptr_t size,
intptr_t alignment,
bool is_executable,
const char* name) {
// See explanation in VirtualMemory::Allocate above.
const bool can_prot_exec = FLAG_write_protect_code;
ASSERT(Utils::IsAligned(size, page_size_));
ASSERT(Utils::IsAligned(alignment, page_size_));
intptr_t allocated_size = size + alignment;
@ -105,8 +118,8 @@ VirtualMemory* VirtualMemory::AllocateAligned(intptr_t size,
zx_object_set_property(vmo, ZX_PROP_NAME, name, strlen(name));
}
if (is_executable) {
// Add ZX_PERM_EXECUTE permission to VMO, so it can be mapped
if (is_executable || can_prot_exec) {
// Add ZX_RIGHT_EXECUTE permission to VMO, so it can be mapped
// into memory as executable.
status = zx_vmo_replace_as_executable(vmo, ZX_HANDLE_INVALID, &vmo);
if (status != ZX_OK) {