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/alpha/mm/tlbflush.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 arch/alpha/mm/tlbflush.c (limited to 'arch/alpha/mm/tlbflush.c') diff --git a/arch/alpha/mm/tlbflush.c b/arch/alpha/mm/tlbflush.c new file mode 100644 index 000000000..ccbc317b9 --- /dev/null +++ b/arch/alpha/mm/tlbflush.c @@ -0,0 +1,112 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Alpha TLB shootdown helpers + * + * Copyright (C) 2025 Magnus Lindholm + * + * Alpha-specific TLB flush helpers that cannot be expressed purely + * as inline functions. + * + * These helpers provide combined MM context handling (ASN rollover) + * and immediate TLB invalidation for page migration and memory + * compaction paths, where lazy shootdowns are insufficient. + */ + +#include +#include +#include +#include +#include +#include + +#define asn_locked() (cpu_data[smp_processor_id()].asn_lock) + +/* + * Migration/compaction helper: combine mm context (ASN) handling with an + * immediate per-page TLB invalidate and (for exec) an instruction barrier. + * + * This mirrors the SMP combined IPI handler semantics, but runs locally on UP. + */ +#ifndef CONFIG_SMP +void migrate_flush_tlb_page(struct vm_area_struct *vma, + unsigned long addr) +{ + struct mm_struct *mm = vma->vm_mm; + int tbi_type = (vma->vm_flags & VM_EXEC) ? 3 : 2; + + /* + * First do the mm-context side: + * If we're currently running this mm, reload a fresh context ASN. + * Otherwise, mark context invalid. + * + * On UP, this is mostly about matching the SMP semantics and ensuring + * exec/i-cache tagging assumptions hold when compaction migrates pages. + */ + if (mm == current->active_mm) + flush_tlb_current(mm); + else + flush_tlb_other(mm); + + /* + * Then do the immediate translation kill for this VA. + * For exec mappings, order instruction fetch after invalidation. + */ + tbi(tbi_type, addr); +} + +#else +struct tlb_mm_and_addr { + struct mm_struct *mm; + unsigned long addr; + int tbi_type; /* 2 = DTB, 3 = ITB+DTB */ +}; + +static void ipi_flush_mm_and_page(void *x) +{ + struct tlb_mm_and_addr *d = x; + + /* Part 1: mm context side (Alpha uses ASN/context as a key mechanism). */ + if (d->mm == current->active_mm && !asn_locked()) + __load_new_mm_context(d->mm); + else + flush_tlb_other(d->mm); + + /* Part 2: immediate per-VA invalidation on this CPU. */ + tbi(d->tbi_type, d->addr); +} + +void migrate_flush_tlb_page(struct vm_area_struct *vma, unsigned long addr) +{ + struct mm_struct *mm = vma->vm_mm; + struct tlb_mm_and_addr d = { + .mm = mm, + .addr = addr, + .tbi_type = (vma->vm_flags & VM_EXEC) ? 3 : 2, + }; + + /* + * One synchronous rendezvous: every CPU runs ipi_flush_mm_and_page(). + * This is the "combined" version of flush_tlb_mm + per-page invalidate. + */ + preempt_disable(); + on_each_cpu(ipi_flush_mm_and_page, &d, 1); + + /* + * mimic flush_tlb_mm()'s mm_users<=1 optimization. + */ + if (atomic_read(&mm->mm_users) <= 1) { + + int cpu, this_cpu; + this_cpu = smp_processor_id(); + + for (cpu = 0; cpu < NR_CPUS; cpu++) { + if (!cpu_online(cpu) || cpu == this_cpu) + continue; + if (READ_ONCE(mm->context[cpu])) + WRITE_ONCE(mm->context[cpu], 0); + } + } + preempt_enable(); +} + +#endif -- cgit v1.3.1