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/mm/maccess.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 arch/x86/mm/maccess.c (limited to 'arch/x86/mm/maccess.c') diff --git a/arch/x86/mm/maccess.c b/arch/x86/mm/maccess.c new file mode 100644 index 000000000..42115ac07 --- /dev/null +++ b/arch/x86/mm/maccess.c @@ -0,0 +1,43 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include +#include + +#include + +#ifdef CONFIG_X86_64 +bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) +{ + unsigned long vaddr = (unsigned long)unsafe_src; + + /* + * Do not allow userspace addresses. This disallows + * normal userspace and the userspace guard page: + */ + if (vaddr < TASK_SIZE_MAX + PAGE_SIZE) + return false; + + /* + * Reading from the vsyscall page may cause an unhandled fault in + * certain cases. Though it is at an address above TASK_SIZE_MAX, it is + * usually considered as a user space address. + */ + if (is_vsyscall_vaddr(vaddr)) + return false; + + /* + * Allow everything during early boot before 'x86_virt_bits' + * is initialized. Needed for instruction decoding in early + * exception handlers. + */ + if (!boot_cpu_data.x86_virt_bits) + return true; + + return __is_canonical_address(vaddr, boot_cpu_data.x86_virt_bits); +} +#else +bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) +{ + return (unsigned long)unsafe_src >= TASK_SIZE_MAX; +} +#endif -- cgit v1.3.1