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/lib/iomem.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 126 insertions(+) create mode 100644 arch/x86/lib/iomem.c (limited to 'arch/x86/lib/iomem.c') diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c new file mode 100644 index 000000000..c20e04764 --- /dev/null +++ b/arch/x86/lib/iomem.c @@ -0,0 +1,126 @@ +#include +#include +#include +#include + +#define movs(type,to,from) \ + asm volatile("movs" type:"=&D" (to), "=&S" (from):"0" (to), "1" (from):"memory") + +/* Originally from i386/string.h */ +static __always_inline void rep_movs(void *to, const void *from, size_t n) +{ + unsigned long d0, d1, d2; + asm volatile("rep movsl\n\t" + "testb $2,%b4\n\t" + "je 1f\n\t" + "movsw\n" + "1:\ttestb $1,%b4\n\t" + "je 2f\n\t" + "movsb\n" + "2:" + : "=&c" (d0), "=&D" (d1), "=&S" (d2) + : "0" (n / 4), "q" (n), "1" ((long)to), "2" ((long)from) + : "memory"); +} + +static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n) +{ + const void *orig_to = to; + const size_t orig_n = n; + + if (unlikely(!n)) + return; + + /* Align any unaligned source IO */ + if (unlikely(1 & (unsigned long)from)) { + movs("b", to, from); + n--; + } + if (n > 1 && unlikely(2 & (unsigned long)from)) { + movs("w", to, from); + n-=2; + } + rep_movs(to, (const void *)from, n); + /* KMSAN must treat values read from devices as initialized. */ + kmsan_unpoison_memory(orig_to, orig_n); +} + +static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n) +{ + if (unlikely(!n)) + return; + + /* Make sure uninitialized memory isn't copied to devices. */ + kmsan_check_memory(from, n); + /* Align any unaligned destination IO */ + if (unlikely(1 & (unsigned long)to)) { + movs("b", to, from); + n--; + } + if (n > 1 && unlikely(2 & (unsigned long)to)) { + movs("w", to, from); + n-=2; + } + rep_movs((void *)to, (const void *) from, n); +} + +static void unrolled_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n) +{ + const volatile char __iomem *in = from; + char *out = to; + int i; + + for (i = 0; i < n; ++i) + out[i] = readb(&in[i]); +} + +static void unrolled_memcpy_toio(volatile void __iomem *to, const void *from, size_t n) +{ + volatile char __iomem *out = to; + const char *in = from; + int i; + + for (i = 0; i < n; ++i) + writeb(in[i], &out[i]); +} + +static void unrolled_memset_io(volatile void __iomem *a, int b, size_t c) +{ + volatile char __iomem *mem = a; + int i; + + for (i = 0; i < c; ++i) + writeb(b, &mem[i]); +} + +void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n) +{ + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) + unrolled_memcpy_fromio(to, from, n); + else + string_memcpy_fromio(to, from, n); +} +EXPORT_SYMBOL(memcpy_fromio); + +void memcpy_toio(volatile void __iomem *to, const void *from, size_t n) +{ + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) + unrolled_memcpy_toio(to, from, n); + else + string_memcpy_toio(to, from, n); +} +EXPORT_SYMBOL(memcpy_toio); + +void memset_io(volatile void __iomem *a, int b, size_t c) +{ + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) { + unrolled_memset_io(a, b, c); + } else { + /* + * TODO: memset can mangle the IO patterns quite a bit. + * perhaps it would be better to use a dumb one: + */ + memset((void *)a, b, c); + } +} +EXPORT_SYMBOL(memset_io); -- cgit v1.3.1