From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- Documentation/filesystems/efivarfs.rst | 43 ++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 Documentation/filesystems/efivarfs.rst (limited to 'Documentation/filesystems/efivarfs.rst') diff --git a/Documentation/filesystems/efivarfs.rst b/Documentation/filesystems/efivarfs.rst new file mode 100644 index 000000000..f646c3f09 --- /dev/null +++ b/Documentation/filesystems/efivarfs.rst @@ -0,0 +1,43 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================= +efivarfs - a (U)EFI variable filesystem +======================================= + +The efivarfs filesystem was created to address the shortcomings of +using entries in sysfs to maintain EFI variables. The old sysfs EFI +variables code only supported variables of up to 1024 bytes. This +limitation existed in version 0.99 of the EFI specification, but was +removed before any full releases. Since variables can now be larger +than a single page, sysfs isn't the best interface for this. + +Variables can be created, deleted and modified with the efivarfs +filesystem. + +efivarfs is typically mounted like this:: + + mount -t efivarfs none /sys/firmware/efi/efivars + +Due to the presence of numerous firmware bugs where removing non-standard +UEFI variables causes the system firmware to fail to POST, efivarfs +files that are not well-known standardized variables are created +as immutable files. This doesn't prevent removal - "chattr -i" will work - +but it does prevent this kind of failure from being accomplished +accidentally. + +.. warning :: + When a content of an UEFI variable in /sys/firmware/efi/efivars is + displayed, for example using "hexdump", pay attention that the first + 4 bytes of the output represent the UEFI variable attributes, + in little-endian format. + + Practically the output of each efivar is composed of: + + +-----------------------------------+ + |4_bytes_of_attributes + efivar_data| + +-----------------------------------+ + +*See also:* + +- Documentation/admin-guide/acpi/ssdt-overlays.rst +- Documentation/ABI/removed/sysfs-firmware-efi-vars -- cgit v1.3.1