selftests/bpf: Reject graph kptr use after RCU unlockgrafted

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 <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/virt/acrn/cpuid.rst b/Documentation/virt/acrn/cpuid.rst
new file mode 100644
index 000000000..65fa4b9c1
--- /dev/null
+++ b/Documentation/virt/acrn/cpuid.rst
@@ -0,0 +1,46 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+ACRN CPUID bits
+===============
+
+A guest VM running on an ACRN hypervisor can check some of its features using
+CPUID.
+
+ACRN cpuid functions are:
+
+function: 0x40000000
+
+returns::
+
+   eax = 0x40000010
+   ebx = 0x4e524341
+   ecx = 0x4e524341
+   edx = 0x4e524341
+
+Note that this value in ebx, ecx and edx corresponds to the string
+"ACRNACRNACRN". The value in eax corresponds to the maximum cpuid function
+present in this leaf, and will be updated if more functions are added in the
+future.
+
+function: define ACRN_CPUID_FEATURES (0x40000001)
+
+returns::
+
+          ebx, ecx, edx
+          eax = an OR'ed group of (1 << flag)
+
+where ``flag`` is defined as below:
+
+================================= =========== ================================
+flag                              value       meaning
+================================= =========== ================================
+ACRN_FEATURE_PRIVILEGED_VM        0           guest VM is a privileged VM
+================================= =========== ================================
+
+function: 0x40000010
+
+returns::
+
+          ebx, ecx, edx
+          eax = (Virtual) TSC frequency in kHz.