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/entry/common.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 arch/x86/entry/common.c (limited to 'arch/x86/entry/common.c') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c new file mode 100644 index 000000000..14cd43d4d --- /dev/null +++ b/arch/x86/entry/common.c @@ -0,0 +1,61 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include +#include +#include +#include + +#if IS_ENABLED(CONFIG_KVM_INTEL) +/* + * On VMX, NMIs and IRQs (as configured by KVM) are acknowledged by hardware as + * part of the VM-Exit, i.e. the event itself is consumed as part the VM-Exit. + * x86_entry_from_kvm() is invoked by KVM to effectively forward NMIs and IRQs + * to the kernel for servicing. On SVM, a.k.a. AMD, the NMI/IRQ VM-Exit is + * purely a signal that an NMI/IRQ is pending, i.e. the event that triggered + * the VM-Exit is held pending until it's unblocked in the host. + */ +noinstr void x86_entry_from_kvm(unsigned int event_type, unsigned int vector) +{ + if (event_type == EVENT_TYPE_EXTINT) { +#ifdef CONFIG_X86_64 + /* + * Use FRED dispatch, even when running IDT. The dispatch + * tables are kept in sync between FRED and IDT, and the FRED + * dispatch works well with CFI. + */ + fred_entry_from_kvm(event_type, vector); +#else + idt_entry_from_kvm(vector); +#endif + /* + * Strictly speaking, only the NMI path requires noinstr. + */ + instrumentation_begin(); + /* + * KVM/VMX will dispatch from IRQ-disabled but for a context + * that will have IRQs-enabled. This confuses the entry code + * and it will not have reprogrammed the timer. Do so now. + */ + hrtimer_rearm_deferred(); + instrumentation_end(); + + return; + } + + WARN_ON_ONCE(event_type != EVENT_TYPE_NMI); + +#ifdef CONFIG_X86_64 + if (cpu_feature_enabled(X86_FEATURE_FRED)) + return fred_entry_from_kvm(event_type, vector); +#endif + + /* + * Notably, we must use IDT dispatch for NMI when running in IDT mode. + * The FRED NMI context is significantly different and will not work + * right (specifically FRED fixed the NMI recursion issue). + */ + idt_do_nmi_irqoff(); +} +EXPORT_SYMBOL_FOR_KVM(x86_entry_from_kvm); +#endif -- cgit v1.3.1