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 --- arch/x86/events/probe.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) create mode 100644 arch/x86/events/probe.c (limited to 'arch/x86/events/probe.c') diff --git a/arch/x86/events/probe.c b/arch/x86/events/probe.c new file mode 100644 index 000000000..bb719d0d3 --- /dev/null +++ b/arch/x86/events/probe.c @@ -0,0 +1,65 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include + +#include +#include "probe.h" + +static umode_t +not_visible(struct kobject *kobj, struct attribute *attr, int i) +{ + return 0; +} + +/* + * Accepts msr[] array with non populated entries as long as either + * msr[i].msr is 0 or msr[i].grp is NULL. Note that the default sysfs + * visibility is visible when group->is_visible callback is set. + */ +unsigned long +perf_msr_probe(struct perf_msr *msr, int cnt, bool zero, void *data) +{ + unsigned long avail = 0; + unsigned int bit; + u64 val; + + if (cnt >= BITS_PER_LONG) + return 0; + + for (bit = 0; bit < cnt; bit++) { + if (!msr[bit].no_check) { + struct attribute_group *grp = msr[bit].grp; + u64 mask; + + /* skip entry with no group */ + if (!grp) + continue; + + grp->is_visible = not_visible; + + /* skip unpopulated entry */ + if (!msr[bit].msr) + continue; + + if (msr[bit].test && !msr[bit].test(bit, data)) + continue; + /* Virt sucks; you cannot tell if a R/O MSR is present :/ */ + if (rdmsrq_safe(msr[bit].msr, &val)) + continue; + + mask = msr[bit].mask; + if (!mask) + mask = ~0ULL; + /* Disable zero counters if requested. */ + if (!zero && !(val & mask)) + continue; + + grp->is_visible = NULL; + } + avail |= BIT(bit); + } + + return avail; +} +EXPORT_SYMBOL_GPL(perf_msr_probe); -- cgit v1.3.1