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, 55 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/fmsub.c b/arch/powerpc/math-emu/fmsub.c
new file mode 100644
index 000000000..605cda49e
--- /dev/null
+++ b/arch/powerpc/math-emu/fmsub.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+
+#include <asm/sfp-machine.h>
+#include <math-emu/soft-fp.h>
+#include <math-emu/double.h>
+
+int
+fmsub(void *frD, void *frA, void *frB, void *frC)
+{
+	FP_DECL_D(R);
+	FP_DECL_D(A);
+	FP_DECL_D(B);
+	FP_DECL_D(C);
+	FP_DECL_D(T);
+	FP_DECL_EX;
+
+#ifdef DEBUG
+	printk("%s: %p %p %p %p\n", __func__, frD, frA, frB, frC);
+#endif
+
+	FP_UNPACK_DP(A, frA);
+	FP_UNPACK_DP(B, frB);
+	FP_UNPACK_DP(C, frC);
+
+#ifdef DEBUG
+	printk("A: %ld %lu %lu %ld (%ld)\n", A_s, A_f1, A_f0, A_e, A_c);
+	printk("B: %ld %lu %lu %ld (%ld)\n", B_s, B_f1, B_f0, B_e, B_c);
+	printk("C: %ld %lu %lu %ld (%ld)\n", C_s, C_f1, C_f0, C_e, C_c);
+#endif
+
+	if ((A_c == FP_CLS_INF && C_c == FP_CLS_ZERO) ||
+	    (A_c == FP_CLS_ZERO && C_c == FP_CLS_INF))
+		FP_SET_EXCEPTION(EFLAG_VXIMZ);
+
+	FP_MUL_D(T, A, C);
+
+	if (B_c != FP_CLS_NAN)
+		B_s ^= 1;
+
+	if (T_s != B_s && T_c == FP_CLS_INF && B_c == FP_CLS_INF)
+		FP_SET_EXCEPTION(EFLAG_VXISI);
+
+	FP_ADD_D(R, T, B);
+
+#ifdef DEBUG
+	printk("D: %ld %lu %lu %ld (%ld)\n", R_s, R_f1, R_f0, R_e, R_c);
+#endif
+
+	__FP_PACK_D(frD, R);
+
+	return FP_CUR_EXCEPTIONS;
+}