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Kernel+Userland: Add ioctl to set process ownership of DisplayConnector

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Now that the infrastructure of the Graphics subsystem is quite stable,
it is time to try to fix a long-standing problem, which is the lack of
locking on display connector devices. Reading and writing from multiple
processes to a framebuffer controlled by the display connector is not a
huge problem - it could be solved with POSIX locking.

The real problem is some program that will try to do ioctl operations on
a display connector without the WindowServer being aware of that which
can lead to very bad situations, for example - assuming a framebuffer is
encoded at a known resolution and certain display timings, but another
process changed the ModeSetting of the display connector, leading to
inconsistency on the properties of the current ModeSetting.

To solve this, there's a new "master" ioctl to take "ownership" and
another one to release that ownership of a display connector device. To
ensure we will not hold a Process object forever just because it has an
ownership over a display connector, we hold it with a weak reference,
and if the process is gone, someone else can take an ownership.
This commit is contained in:
Liav A 2022-06-10 14:16:28 +03:00 • committed by Linus Groh
parent 1968aba69b
commit 977aa81310
5 changed files with 101 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

10
Kernel/API/Graphics.h
View file

@ -50,6 +50,16 @@ ALWAYS_INLINE int graphics_connector_get_head_edid(int fd, GraphicsHeadEDID* inf
return 0;
}
ALWAYS_INLINE int graphics_connector_set_responsible(int fd)
{
return ioctl(fd, GRAPHICS_IOCTL_SET_RESPONSIBLE, nullptr);
}
ALWAYS_INLINE int graphics_connector_unset_responsible(int fd)
{
return ioctl(fd, GRAPHICS_IOCTL_UNSET_RESPONSIBLE, nullptr);
}
ALWAYS_INLINE int fb_get_head_vertical_offset_buffer(int fd, GraphicsHeadVerticalOffset* vertical_offset)
{
return ioctl(fd, GRAPHICS_IOCTL_GET_HEAD_VERTICAL_OFFSET_BUFFER, vertical_offset);

70
Kernel/Graphics/DisplayConnector.cpp
View file

@ -231,11 +231,81 @@ ErrorOr<ByteBuffer> DisplayConnector::get_edid() const
return ByteBuffer::copy(m_edid_bytes, sizeof(m_edid_bytes));
}
struct GraphicsIOCtlChecker {
unsigned ioctl_number;
StringView name;
bool requires_ownership { false };
};
static constexpr GraphicsIOCtlChecker s_checkers[] = {
{ GRAPHICS_IOCTL_GET_PROPERTIES, "GRAPHICS_IOCTL_GET_PROPERTIES"sv, false },
{ GRAPHICS_IOCTL_SET_HEAD_VERTICAL_OFFSET_BUFFER, "GRAPHICS_IOCTL_SET_HEAD_VERTICAL_OFFSET_BUFFER"sv, true },
{ GRAPHICS_IOCTL_GET_HEAD_VERTICAL_OFFSET_BUFFER, "GRAPHICS_IOCTL_GET_HEAD_VERTICAL_OFFSET_BUFFER"sv, false },
{ GRAPHICS_IOCTL_FLUSH_HEAD_BUFFERS, "GRAPHICS_IOCTL_FLUSH_HEAD_BUFFERS"sv, true },
{ GRAPHICS_IOCTL_FLUSH_HEAD, "GRAPHICS_IOCTL_FLUSH_HEAD"sv, true },
{ GRAPHICS_IOCTL_SET_HEAD_MODE_SETTING, "GRAPHICS_IOCTL_SET_HEAD_MODE_SETTING"sv, true },
{ GRAPHICS_IOCTL_GET_HEAD_MODE_SETTING, "GRAPHICS_IOCTL_GET_HEAD_MODE_SETTING"sv, false },
{ GRAPHICS_IOCTL_SET_SAFE_HEAD_MODE_SETTING, "GRAPHICS_IOCTL_SET_SAFE_HEAD_MODE_SETTING"sv, true },
{ GRAPHICS_IOCTL_SET_RESPONSIBLE, "GRAPHICS_IOCTL_SET_RESPONSIBLE"sv, false },
{ GRAPHICS_IOCTL_UNSET_RESPONSIBLE, "GRAPHICS_IOCTL_UNSET_RESPONSIBLE"sv, true },
};
static StringView ioctl_to_stringview(unsigned request)
{
for (auto& checker : s_checkers) {
if (checker.ioctl_number == request)
return checker.name;
}
VERIFY_NOT_REACHED();
}
bool DisplayConnector::ioctl_requires_ownership(unsigned request) const
{
for (auto& checker : s_checkers) {
if (checker.ioctl_number == request)
return checker.requires_ownership;
}
VERIFY_NOT_REACHED();
}
ErrorOr<void> DisplayConnector::ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg)
{
TRY(Process::current().require_promise(Pledge::video));
// Note: We only allow to set responsibility on a DisplayConnector,
// get the current ModeSetting or the hardware framebuffer properties without the
// need of having an established responsibility on a DisplayConnector.
if (ioctl_requires_ownership(request)) {
auto process = m_responsible_process.strong_ref();
if (!process || process.ptr() != &Process::current()) {
dbgln("DisplayConnector::ioctl: {} requires ownership over the device", ioctl_to_stringview(request));
return Error::from_errno(EPERM);
}
}
switch (request) {
case GRAPHICS_IOCTL_SET_RESPONSIBLE: {
SpinlockLocker locker(m_responsible_process_lock);
auto process = m_responsible_process.strong_ref();
// Note: If there's already a process being responsible, just return an error.
// We could technically return 0 if the the requesting process is already
// was set to be responsible for this DisplayConnector, but it servicing no
// no good purpose and should be considered a bug if this happens anyway.
if (process)
return Error::from_errno(EPERM);
m_responsible_process = Process::current();
return {};
}
case GRAPHICS_IOCTL_UNSET_RESPONSIBLE: {
SpinlockLocker locker(m_responsible_process_lock);
auto process = m_responsible_process.strong_ref();
if (!process)
return Error::from_errno(ESRCH);
if (process.ptr() != &Process::current())
return Error::from_errno(EPERM);
m_responsible_process.clear();
return {};
}
case GRAPHICS_IOCTL_GET_PROPERTIES: {
auto user_properties = static_ptr_cast<GraphicsConnectorProperties*>(arg);
GraphicsConnectorProperties properties {};

5
Kernel/Graphics/DisplayConnector.h
View file

@ -148,6 +148,8 @@ private:
virtual void will_be_destroyed() override;
virtual void after_inserting() override;
bool ioctl_requires_ownership(unsigned request) const;
OwnPtr<Memory::Region> m_framebuffer_region;
OwnPtr<Memory::Region> m_fake_writes_framebuffer_region;
u8* m_framebuffer_data {};
@ -162,6 +164,9 @@ protected:
private:
RefPtr<Memory::SharedFramebufferVMObject> m_shared_framebuffer_vmobject;
WeakPtr<Process> m_responsible_process;
Spinlock m_responsible_process_lock;
IntrusiveListNode<DisplayConnector, RefPtr<DisplayConnector>> m_list_node;
};
}

4
Userland/Libraries/LibC/sys/ioctl_numbers.h
View file

@ -101,6 +101,8 @@ enum IOCtlNumber {
GRAPHICS_IOCTL_SET_HEAD_MODE_SETTING,
GRAPHICS_IOCTL_GET_HEAD_MODE_SETTING,
GRAPHICS_IOCTL_SET_SAFE_HEAD_MODE_SETTING,
GRAPHICS_IOCTL_SET_RESPONSIBLE,
GRAPHICS_IOCTL_UNSET_RESPONSIBLE,
KEYBOARD_IOCTL_GET_NUM_LOCK,
KEYBOARD_IOCTL_SET_NUM_LOCK,
KEYBOARD_IOCTL_GET_CAPS_LOCK,
@ -160,6 +162,8 @@ enum IOCtlNumber {
#define GRAPHICS_IOCTL_SET_HEAD_MODE_SETTING GRAPHICS_IOCTL_SET_HEAD_MODE_SETTING
#define GRAPHICS_IOCTL_GET_HEAD_MODE_SETTING GRAPHICS_IOCTL_GET_HEAD_MODE_SETTING
#define GRAPHICS_IOCTL_SET_SAFE_HEAD_MODE_SETTING GRAPHICS_IOCTL_SET_SAFE_HEAD_MODE_SETTING
#define GRAPHICS_IOCTL_SET_RESPONSIBLE GRAPHICS_IOCTL_SET_RESPONSIBLE
#define GRAPHICS_IOCTL_UNSET_RESPONSIBLE GRAPHICS_IOCTL_UNSET_RESPONSIBLE
#define KEYBOARD_IOCTL_GET_NUM_LOCK KEYBOARD_IOCTL_GET_NUM_LOCK
#define KEYBOARD_IOCTL_SET_NUM_LOCK KEYBOARD_IOCTL_SET_NUM_LOCK
#define KEYBOARD_IOCTL_GET_CAPS_LOCK KEYBOARD_IOCTL_GET_CAPS_LOCK

20
Userland/Services/WindowServer/main.cpp
View file

@ -9,6 +9,7 @@
#include "EventLoop.h"
#include "Screen.h"
#include "WindowManager.h"
#include <Kernel/API/Graphics.h>
#include <LibCore/ConfigFile.h>
#include <LibCore/DirIterator.h>
#include <LibCore/File.h>
@ -68,7 +69,7 @@ ErrorOr<int> serenity_main(Main::Arguments)
WindowServer::ScreenLayout screen_layout;
String error_msg;
auto add_unconfigured_display_connector_devices = [&]() {
auto add_unconfigured_display_connector_devices = [&]() -> ErrorOr<void> {
// Enumerate the /dev/gpu/connectorX devices and try to set up any ones we find that we haven't already used
Core::DirIterator di("/dev/gpu", Core::DirIterator::SkipParentAndBaseDir);
while (di.has_next()) {
@ -78,18 +79,23 @@ ErrorOr<int> serenity_main(Main::Arguments)
auto full_path = String::formatted("/dev/gpu/{}", path);
if (!Core::File::is_device(full_path))
continue;
auto display_connector_fd = TRY(Core::System::open(full_path, O_RDWR | O_CLOEXEC));
if (int rc = graphics_connector_set_responsible(display_connector_fd); rc != 0)
return Error::from_syscall("graphics_connector_set_responsible"sv, rc);
TRY(Core::System::close(display_connector_fd));
if (fb_devices_configured.find(full_path) != fb_devices_configured.end())
continue;
if (!screen_layout.try_auto_add_display_connector(full_path))
dbgln("Could not auto-add display connector device {} to screen layout", full_path);
}
return {};
};
auto apply_and_generate_generic_screen_layout = [&]() {
auto apply_and_generate_generic_screen_layout = [&]() -> ErrorOr<bool> {
screen_layout = {};
fb_devices_configured = {};
add_unconfigured_display_connector_devices();
TRY(add_unconfigured_display_connector_devices());
if (!WindowServer::Screen::apply_layout(move(screen_layout), error_msg)) {
dbgln("Failed to apply generated fallback screen layout: {}", error_msg);
return false;
@ -104,17 +110,15 @@ ErrorOr<int> serenity_main(Main::Arguments)
if (screen_info.mode == WindowServer::ScreenLayout::Screen::Mode::Device)
fb_devices_configured.set(screen_info.device.value());
add_unconfigured_display_connector_devices();
TRY(add_unconfigured_display_connector_devices());
if (!WindowServer::Screen::apply_layout(move(screen_layout), error_msg)) {
dbgln("Error applying screen layout: {}", error_msg);
if (!apply_and_generate_generic_screen_layout())
return 1;
TRY(apply_and_generate_generic_screen_layout());
}
} else {
dbgln("Error loading screen configuration: {}", error_msg);
if (!apply_and_generate_generic_screen_layout())
return 1;
TRY(apply_and_generate_generic_screen_layout());
}
}