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 --- include/asm-generic/pgtable-nopmd.h | 73 +++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 include/asm-generic/pgtable-nopmd.h (limited to 'include/asm-generic/pgtable-nopmd.h') diff --git a/include/asm-generic/pgtable-nopmd.h b/include/asm-generic/pgtable-nopmd.h new file mode 100644 index 000000000..8ffd64e7a --- /dev/null +++ b/include/asm-generic/pgtable-nopmd.h @@ -0,0 +1,73 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _PGTABLE_NOPMD_H +#define _PGTABLE_NOPMD_H + +#ifndef __ASSEMBLY__ + +#include + +struct mm_struct; + +#define __PAGETABLE_PMD_FOLDED 1 + +/* + * Having the pmd type consist of a pud gets the size right, and allows + * us to conceptually access the pud entry that this pmd is folded into + * without casting. + */ +typedef struct { pud_t pud; } pmd_t; + +#define PMD_SHIFT PUD_SHIFT +#define PTRS_PER_PMD 1 +#define PMD_SIZE (1UL << PMD_SHIFT) +#define PMD_MASK (~(PMD_SIZE-1)) + +/* + * The "pud_xxx()" functions here are trivial for a folded two-level + * setup: the pmd is never bad, and a pmd always exists (as it's folded + * into the pud entry) + */ +static inline int pud_none(pud_t pud) { return 0; } +static inline int pud_bad(pud_t pud) { return 0; } +static inline int pud_present(pud_t pud) { return 1; } +static inline int pud_user(pud_t pud) { return 0; } +static inline int pud_leaf(pud_t pud) { return 0; } +static inline void pud_clear(pud_t *pud) { } +#define pmd_ERROR(pmd) (pud_ERROR((pmd).pud)) + +#define pud_populate(mm, pmd, pte) do { } while (0) + +/* + * (pmds are folded into puds so this doesn't get actually called, + * but the define is needed for a generic inline function.) + */ +#define set_pud(pudptr, pudval) set_pmd((pmd_t *)(pudptr), (pmd_t) { pudval }) + +static inline pmd_t * pmd_offset(pud_t * pud, unsigned long address) +{ + return (pmd_t *)pud; +} +#define pmd_offset pmd_offset + +#define pmd_val(x) (pud_val((x).pud)) +#define __pmd(x) ((pmd_t) { __pud(x) } ) + +#define pud_page(pud) (pmd_page((pmd_t){ pud })) +#define pud_pgtable(pud) ((pmd_t *)(pmd_page_vaddr((pmd_t){ pud }))) + +/* + * allocating and freeing a pmd is trivial: the 1-entry pmd is + * inside the pud, so has no extra memory associated with it. + */ +#define pmd_alloc_one(mm, address) NULL +static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd) +{ +} +#define pmd_free_tlb(tlb, x, a) do { } while (0) + +#undef pmd_addr_end +#define pmd_addr_end(addr, end) (end) + +#endif /* __ASSEMBLY__ */ + +#endif /* _PGTABLE_NOPMD_H */ -- cgit v1.3.1