selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/Documentation/admin-guide/LSM/LoadPin.rst b/Documentation/admin-guide/LSM/LoadPin.rst
new file mode 100644
index 000000000..dd3ca68b5
--- /dev/null
+++ b/Documentation/admin-guide/LSM/LoadPin.rst
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+=======
+LoadPin
+=======
+
+LoadPin is a Linux Security Module that ensures all kernel-loaded files
+(modules, firmware, etc) all originate from the same filesystem, with
+the expectation that such a filesystem is backed by a read-only device
+such as dm-verity or CDROM. This allows systems that have a verified
+and/or unchangeable filesystem to enforce module and firmware loading
+restrictions without needing to sign the files individually.
+
+The LSM is selectable at build-time with ``CONFIG_SECURITY_LOADPIN``, and
+can be controlled at boot-time with the kernel command line option
+"``loadpin.enforce``". By default, it is enabled, but can be disabled at
+boot ("``loadpin.enforce=0``").
+
+LoadPin starts pinning when it sees the first file loaded. If the
+block device backing the filesystem is not read-only, a sysctl is
+created to toggle pinning: ``/proc/sys/kernel/loadpin/enabled``. (Having
+a mutable filesystem means pinning is mutable too, but having the
+sysctl allows for easy testing on systems with a mutable filesystem.)
+
+It's also possible to exclude specific file types from LoadPin using kernel
+command line option "``loadpin.exclude``". By default, all files are
+included, but they can be excluded using kernel command line option such
+as "``loadpin.exclude=kernel-module,kexec-image``". This allows to use
+different mechanisms such as ``CONFIG_MODULE_SIG`` and
+``CONFIG_KEXEC_VERIFY_SIG`` to verify kernel module and kernel image while
+still use LoadPin to protect the integrity of other files kernel loads. The
+full list of valid file types can be found in ``kernel_read_file_str``
+defined in ``include/linux/kernel_read_file.h``.