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/cmpxchg.h | 115 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) create mode 100644 include/asm-generic/cmpxchg.h (limited to 'include/asm-generic/cmpxchg.h') diff --git a/include/asm-generic/cmpxchg.h b/include/asm-generic/cmpxchg.h new file mode 100644 index 000000000..848de25fc --- /dev/null +++ b/include/asm-generic/cmpxchg.h @@ -0,0 +1,115 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Generic UP xchg and cmpxchg using interrupt disablement. Does not + * support SMP. + */ + +#ifndef __ASM_GENERIC_CMPXCHG_H +#define __ASM_GENERIC_CMPXCHG_H + +#ifdef CONFIG_SMP +#error "Cannot use generic cmpxchg on SMP" +#endif + +#include +#include + +/* + * This function doesn't exist, so you'll get a linker error if + * something tries to do an invalidly-sized xchg(). + */ +extern void __generic_xchg_called_with_bad_pointer(void); + +static inline +unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size) +{ + unsigned long ret, flags; + + switch (size) { + case 1: +#ifdef __xchg_u8 + return __xchg_u8(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u8 *)ptr; + *(volatile u8 *)ptr = (x & 0xffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u8 */ + + case 2: +#ifdef __xchg_u16 + return __xchg_u16(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u16 *)ptr; + *(volatile u16 *)ptr = (x & 0xffffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u16 */ + + case 4: +#ifdef __xchg_u32 + return __xchg_u32(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u32 *)ptr; + *(volatile u32 *)ptr = (x & 0xffffffffu); + local_irq_restore(flags); + return ret; +#endif /* __xchg_u32 */ + +#ifdef CONFIG_64BIT + case 8: +#ifdef __xchg_u64 + return __xchg_u64(x, ptr); +#else + local_irq_save(flags); + ret = *(volatile u64 *)ptr; + *(volatile u64 *)ptr = x; + local_irq_restore(flags); + return ret; +#endif /* __xchg_u64 */ +#endif /* CONFIG_64BIT */ + + default: + __generic_xchg_called_with_bad_pointer(); + return x; + } +} + +#define generic_xchg(ptr, x) ({ \ + ((__typeof__(*(ptr))) \ + __generic_xchg((unsigned long)(x), (ptr), sizeof(*(ptr)))); \ +}) + +/* + * Atomic compare and exchange. + */ +#include + +#define generic_cmpxchg_local(ptr, o, n) ({ \ + ((__typeof__(*(ptr)))__generic_cmpxchg_local((ptr), (unsigned long)(o), \ + (unsigned long)(n), sizeof(*(ptr)))); \ +}) + +#define generic_cmpxchg64_local(ptr, o, n) \ + __generic_cmpxchg64_local((ptr), (o), (n)) + + +#ifndef arch_xchg +#define arch_xchg generic_xchg +#endif + +#ifndef arch_cmpxchg_local +#define arch_cmpxchg_local generic_cmpxchg_local +#endif + +#ifndef arch_cmpxchg64_local +#define arch_cmpxchg64_local generic_cmpxchg64_local +#endif + +#define arch_cmpxchg arch_cmpxchg_local +#define arch_cmpxchg64 arch_cmpxchg64_local + +#endif /* __ASM_GENERIC_CMPXCHG_H */ -- cgit v1.3.1