From 27600805e62f800bacf990354632eae4e487d34c Mon Sep 17 00:00:00 2001 From: Yazen Ghannam Date: Thu, 3 Sep 2026 10:43:25 -0500 Subject: x86/amd_node: Fix PCI device reference counting in amd_smn_init() The local "root" pointer is a temporary variable used during the device search. Therefore, refcount related to the search iterators should be cleaned up after the search is complete. Use the __free() cleanup macro to ensure the refcount is decremented when the temporary pointer goes out of scope. Additionally, increment the refcount when caching a root pointer. This ensures the in-use refcount is separate from the temporary search refcounting. Finally, drop the redundant "root = NULL" before the second search loop. The pci_get_class() iterator always decrements the refcount of its "from" argument, so the first loop can only fall through with "root" already NULL. Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com Reported-by: Sashiko Assisted-by: LLM Signed-off-by: Yazen Ghannam Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Mario Limonciello (AMD) Cc: Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com --- Documentation/userspace-api/mfd_noexec.rst | 86 ++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 Documentation/userspace-api/mfd_noexec.rst (limited to 'Documentation/userspace-api/mfd_noexec.rst') diff --git a/Documentation/userspace-api/mfd_noexec.rst b/Documentation/userspace-api/mfd_noexec.rst new file mode 100644 index 000000000..7afcc480e --- /dev/null +++ b/Documentation/userspace-api/mfd_noexec.rst @@ -0,0 +1,86 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================== +Introduction of non-executable mfd +================================== +:Author: + Daniel Verkamp + Jeff Xu + +:Contributor: + Aleksa Sarai + +Since Linux introduced the memfd feature, memfds have always had their +execute bit set, and the memfd_create() syscall doesn't allow setting +it differently. + +However, in a secure-by-default system, such as ChromeOS, (where all +executables should come from the rootfs, which is protected by verified +boot), this executable nature of memfd opens a door for NoExec bypass +and enables “confused deputy attack”. E.g, in VRP bug [1]: cros_vm +process created a memfd to share the content with an external process, +however the memfd is overwritten and used for executing arbitrary code +and root escalation. [2] lists more VRP of this kind. + +On the other hand, executable memfd has its legit use: runc uses memfd’s +seal and executable feature to copy the contents of the binary then +execute them. For such a system, we need a solution to differentiate runc's +use of executable memfds and an attacker's [3]. + +To address those above: + - Let memfd_create() set X bit at creation time. + - Let memfd be sealed for modifying X bit when NX is set. + - Add a new pid namespace sysctl: vm.memfd_noexec to help applications in + migrating and enforcing non-executable MFD. + +User API +======== +``int memfd_create(const char *name, unsigned int flags)`` + +``MFD_NOEXEC_SEAL`` + When MFD_NOEXEC_SEAL bit is set in the ``flags``, memfd is created + with NX. F_SEAL_EXEC is set and the memfd can't be modified to + add X later. MFD_ALLOW_SEALING is also implied. + This is the most common case for the application to use memfd. + +``MFD_EXEC`` + When MFD_EXEC bit is set in the ``flags``, memfd is created with X. + +Note: + ``MFD_NOEXEC_SEAL`` implies ``MFD_ALLOW_SEALING``. In case that + an app doesn't want sealing, it can add F_SEAL_SEAL after creation. + + +Sysctl: +======== +``pid namespaced sysctl vm.memfd_noexec`` + +The new pid namespaced sysctl vm.memfd_noexec has 3 values: + + - 0: MEMFD_NOEXEC_SCOPE_EXEC + memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_EXEC was set. + + - 1: MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL + memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_NOEXEC_SEAL was set. + + - 2: MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED + memfd_create() without MFD_NOEXEC_SEAL will be rejected. + +The sysctl allows finer control of memfd_create for old software that +doesn't set the executable bit; for example, a container with +vm.memfd_noexec=1 means the old software will create non-executable memfd +by default while new software can create executable memfd by setting +MFD_EXEC. + +The value of vm.memfd_noexec is passed to child namespace at creation +time. In addition, the setting is hierarchical, i.e. during memfd_create, +we will search from current ns to root ns and use the most restrictive +setting. + +[1] https://crbug.com/1305267 + +[2] https://bugs.chromium.org/p/chromium/issues/list?q=type%3Dbug-security%20memfd%20escalation&can=1 + +[3] https://lwn.net/Articles/781013/ -- cgit v1.3.1