selftests/bpf: Reject graph kptr use after RCU unlockgrafted

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 <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 126 insertions, 0 deletions

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 <linux/string.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/kmsan-checks.h>
+
+#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);