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https://github.com/RGBCube/serenity
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Kernel: Make copy_to/from_user safe and remove unnecessary checks
Since the CPU already does almost all necessary validation steps for us, we don't really need to attempt to do this. Doing it ourselves doesn't really work very reliably, because we'd have to account for other processors modifying virtual memory, and we'd have to account for e.g. pages not being able to be allocated due to insufficient resources. So change the copy_to/from_user (and associated helper functions) to use the new safe_memcpy, which will return whether it succeeded or not. The only manual validation step needed (which the CPU can't perform for us) is making sure the pointers provided by user mode aren't pointing to kernel mappings. To make it easier to read/write from/to either kernel or user mode data add the UserOrKernelBuffer helper class, which will internally either use copy_from/to_user or directly memcpy, or pass the data through directly using a temporary buffer on the stack. Last but not least we need to keep syscall params trivial as we need to copy them from/to user mode using copy_from/to_user.
This commit is contained in:
Tom
Andreas Kling
parent
7d1b8417bd
commit
c8d9f1b9c9
149 changed files with 1585 additions and 1244 deletions
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@ -34,51 +34,43 @@
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namespace Kernel {
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int Process::sys$select(const Syscall::SC_select_params* params)
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int Process::sys$select(const Syscall::SC_select_params* user_params)
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{
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REQUIRE_PROMISE(stdio);
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// FIXME: Return -EINVAL if timeout is invalid.
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if (!validate_read_typed(params))
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return -EFAULT;
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Syscall::SC_select_params params;
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SmapDisabler disabler;
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if (!copy_from_user(¶ms, user_params))
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return -EFAULT;
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int nfds = params->nfds;
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fd_set* readfds = params->readfds;
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fd_set* writefds = params->writefds;
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fd_set* exceptfds = params->exceptfds;
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const timespec* timeout = params->timeout;
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const sigset_t* sigmask = params->sigmask;
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if (writefds && !validate_write_typed(writefds))
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return -EFAULT;
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if (readfds && !validate_write_typed(readfds))
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return -EFAULT;
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if (exceptfds && !validate_write_typed(exceptfds))
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return -EFAULT;
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if (timeout && !validate_read_typed(timeout))
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return -EFAULT;
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if (sigmask && !validate_read_typed(sigmask))
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return -EFAULT;
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if (nfds < 0)
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if (params.nfds < 0)
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return -EINVAL;
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timespec computed_timeout;
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bool select_has_timeout = false;
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if (timeout && (timeout->tv_sec || timeout->tv_nsec)) {
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timespec ts_since_boot;
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timeval_to_timespec(Scheduler::time_since_boot(), ts_since_boot);
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timespec_add(ts_since_boot, *timeout, computed_timeout);
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select_has_timeout = true;
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if (params.timeout) {
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timespec timeout_copy;
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if (!copy_from_user(&timeout_copy, params.timeout))
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return -EFAULT;
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if (timeout_copy.tv_sec || timeout_copy.tv_nsec) {
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timespec ts_since_boot;
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timeval_to_timespec(Scheduler::time_since_boot(), ts_since_boot);
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timespec_add(ts_since_boot, timeout_copy, computed_timeout);
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select_has_timeout = true;
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}
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}
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auto current_thread = Thread::current();
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u32 previous_signal_mask = 0;
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if (sigmask)
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previous_signal_mask = current_thread->update_signal_mask(*sigmask);
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if (params.sigmask) {
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sigset_t sigmask_copy;
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if (!copy_from_user(&sigmask_copy, params.sigmask))
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return -EFAULT;
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previous_signal_mask = current_thread->update_signal_mask(sigmask_copy);
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}
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ScopeGuard rollback_signal_mask([&]() {
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if (sigmask)
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if (params.sigmask)
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current_thread->update_signal_mask(previous_signal_mask);
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});
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@ -86,12 +78,15 @@ int Process::sys$select(const Syscall::SC_select_params* params)
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Thread::SelectBlocker::FDVector wfds;
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Thread::SelectBlocker::FDVector efds;
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auto transfer_fds = [&](auto* fds, auto& vector) -> int {
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auto transfer_fds = [&](auto* fds_unsafe, auto& vector) -> int {
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vector.clear_with_capacity();
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if (!fds)
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if (!fds_unsafe)
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return 0;
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for (int fd = 0; fd < nfds; ++fd) {
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if (FD_ISSET(fd, fds)) {
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fd_set fds;
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if (!copy_from_user(&fds, fds_unsafe))
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return -EFAULT;
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for (int fd = 0; fd < params.nfds; ++fd) {
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if (FD_ISSET(fd, &fds)) {
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if (!file_description(fd)) {
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dbg() << "sys$select: Bad fd number " << fd;
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return -EBADF;
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@ -101,47 +96,42 @@ int Process::sys$select(const Syscall::SC_select_params* params)
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}
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return 0;
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};
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if (int error = transfer_fds(writefds, wfds))
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if (int error = transfer_fds(params.writefds, wfds))
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return error;
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if (int error = transfer_fds(readfds, rfds))
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if (int error = transfer_fds(params.readfds, rfds))
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return error;
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if (int error = transfer_fds(exceptfds, efds))
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if (int error = transfer_fds(params.exceptfds, efds))
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return error;
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#if defined(DEBUG_IO) || defined(DEBUG_POLL_SELECT)
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dbg() << "selecting on (read:" << rfds.size() << ", write:" << wfds.size() << "), timeout=" << timeout;
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dbg() << "selecting on (read:" << rfds.size() << ", write:" << wfds.size() << "), timeout=" << params.timeout;
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#endif
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if (!timeout || select_has_timeout) {
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if (!params.timeout || select_has_timeout) {
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if (current_thread->block<Thread::SelectBlocker>(select_has_timeout ? &computed_timeout : nullptr, rfds, wfds, efds).was_interrupted())
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return -EINTR;
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// While we blocked, the process lock was dropped. This gave other threads
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// the opportunity to mess with the memory. For example, it could free the
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// region, and map it to a region to which it has no write permissions.
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// Therefore, we need to re-validate all pointers.
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if (writefds && !validate_write_typed(writefds))
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return -EFAULT;
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if (readfds && !validate_write_typed(readfds))
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return -EFAULT;
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// See the fixme below.
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if (exceptfds && !validate_write_typed(exceptfds))
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return -EFAULT;
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}
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int marked_fd_count = 0;
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auto mark_fds = [&](auto* fds, auto& vector, auto should_mark) {
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if (!fds)
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return;
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FD_ZERO(fds);
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auto mark_fds = [&](auto* fds_unsafe, auto& vector, auto should_mark) {
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if (!fds_unsafe)
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return 0;
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fd_set fds;
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FD_ZERO(&fds);
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for (int fd : vector) {
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if (auto description = file_description(fd); description && should_mark(*description)) {
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FD_SET(fd, fds);
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FD_SET(fd, &fds);
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++marked_fd_count;
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}
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}
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if (!copy_to_user(fds_unsafe, &fds))
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return -EFAULT;
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return 0;
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};
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mark_fds(readfds, rfds, [](auto& description) { return description.can_read(); });
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mark_fds(writefds, wfds, [](auto& description) { return description.can_write(); });
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if (int error = mark_fds(params.readfds, rfds, [](auto& description) { return description.can_read(); }))
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return error;
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if (int error = mark_fds(params.writefds, wfds, [](auto& description) { return description.can_write(); }))
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return error;
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// FIXME: We should also mark exceptfds as appropriate.
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return marked_fd_count;
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@ -153,33 +143,39 @@ int Process::sys$poll(Userspace<const Syscall::SC_poll_params*> user_params)
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// FIXME: Return -EINVAL if timeout is invalid.
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Syscall::SC_poll_params params;
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if (!validate_read_and_copy_typed(¶ms, user_params))
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if (!copy_from_user(¶ms, user_params))
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return -EFAULT;
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SmapDisabler disabler;
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pollfd* fds = params.fds;
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unsigned nfds = params.nfds;
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if (fds && !validate_read_typed(fds, nfds))
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return -EFAULT;
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timespec timeout = {};
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if (params.timeout && !validate_read_and_copy_typed(&timeout, params.timeout))
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if (params.timeout && !copy_from_user(&timeout, params.timeout))
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return -EFAULT;
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sigset_t sigmask = {};
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if (params.sigmask && !validate_read_and_copy_typed(&sigmask, params.sigmask))
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if (params.sigmask && !copy_from_user(&sigmask, params.sigmask))
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return -EFAULT;
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Vector<pollfd> fds_copy;
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if (params.nfds > 0) {
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Checked nfds_checked = sizeof(pollfd);
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nfds_checked *= params.nfds;
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if (nfds_checked.has_overflow())
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return -EFAULT;
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fds_copy.resize(params.nfds);
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if (!copy_from_user(&fds_copy[0], ¶ms.fds[0], params.nfds * sizeof(pollfd)))
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return -EFAULT;
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}
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Thread::SelectBlocker::FDVector rfds;
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Thread::SelectBlocker::FDVector wfds;
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for (unsigned i = 0; i < nfds; ++i) {
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if (fds[i].events & POLLIN)
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rfds.append(fds[i].fd);
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if (fds[i].events & POLLOUT)
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wfds.append(fds[i].fd);
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for (unsigned i = 0; i < params.nfds; ++i) {
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auto& pfd = fds_copy[i];
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if (pfd.events & POLLIN)
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rfds.append(pfd.fd);
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if (pfd.events & POLLOUT)
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wfds.append(pfd.fd);
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}
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timespec actual_timeout;
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@ -195,7 +191,7 @@ int Process::sys$poll(Userspace<const Syscall::SC_poll_params*> user_params)
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u32 previous_signal_mask = 0;
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if (params.sigmask)
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previous_signal_mask = current_thread->update_signal_mask(params.sigmask);
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previous_signal_mask = current_thread->update_signal_mask(sigmask);
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ScopeGuard rollback_signal_mask([&]() {
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if (params.sigmask)
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current_thread->update_signal_mask(previous_signal_mask);
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@ -210,28 +206,28 @@ int Process::sys$poll(Userspace<const Syscall::SC_poll_params*> user_params)
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return -EINTR;
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}
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// Validate we can still write after waking up.
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if (fds && !validate_write_typed(fds, nfds))
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return -EFAULT;
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int fds_with_revents = 0;
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for (unsigned i = 0; i < nfds; ++i) {
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auto description = file_description(fds[i].fd);
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for (unsigned i = 0; i < params.nfds; ++i) {
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auto& pfd = fds_copy[i];
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auto description = file_description(pfd.fd);
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if (!description) {
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fds[i].revents = POLLNVAL;
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continue;
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}
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fds[i].revents = 0;
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if (fds[i].events & POLLIN && description->can_read())
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fds[i].revents |= POLLIN;
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if (fds[i].events & POLLOUT && description->can_write())
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fds[i].revents |= POLLOUT;
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pfd.revents = POLLNVAL;
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} else {
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pfd.revents = 0;
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if (pfd.events & POLLIN && description->can_read())
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pfd.revents |= POLLIN;
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if (pfd.events & POLLOUT && description->can_write())
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pfd.revents |= POLLOUT;
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if (fds[i].revents)
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++fds_with_revents;
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if (pfd.revents)
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++fds_with_revents;
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}
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}
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if (params.nfds > 0 && !copy_to_user(¶ms.fds[0], &fds_copy[0], params.nfds * sizeof(pollfd)))
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return -EFAULT;
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return fds_with_revents;
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}
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