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, 52 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/mtfsf.c b/arch/powerpc/math-emu/mtfsf.c
new file mode 100644
index 000000000..7ae990f6b
--- /dev/null
+++ b/arch/powerpc/math-emu/mtfsf.c
@@ -0,0 +1,52 @@
+// 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>
+
+int
+mtfsf(unsigned int FM, u32 *frB)
+{
+	u32 mask;
+	u32 fpscr;
+
+	if (likely(FM == 1))
+		mask = 0x0f;
+	else if (likely(FM == 0xff))
+		mask = ~0;
+	else {
+		mask = ((FM & 1) |
+				((FM << 3) & 0x10) |
+				((FM << 6) & 0x100) |
+				((FM << 9) & 0x1000) |
+				((FM << 12) & 0x10000) |
+				((FM << 15) & 0x100000) |
+				((FM << 18) & 0x1000000) |
+				((FM << 21) & 0x10000000)) * 15;
+	}
+
+	fpscr = ((__FPU_FPSCR & ~mask) | (frB[1] & mask)) &
+		~(FPSCR_VX | FPSCR_FEX | 0x800);
+
+	if (fpscr & (FPSCR_VXSNAN | FPSCR_VXISI | FPSCR_VXIDI |
+		     FPSCR_VXZDZ | FPSCR_VXIMZ | FPSCR_VXVC |
+		     FPSCR_VXSOFT | FPSCR_VXSQRT | FPSCR_VXCVI))
+		fpscr |= FPSCR_VX;
+
+	/* The bit order of exception enables and exception status
+	 * is the same. Simply shift and mask to check for enabled
+	 * exceptions.
+	 */
+	if (fpscr & (fpscr >> 22) &  0xf8)
+		fpscr |= FPSCR_FEX;
+
+	__FPU_FPSCR = fpscr;
+
+#ifdef DEBUG
+	printk("%s: %02x %p: %08lx\n", __func__, FM, frB, __FPU_FPSCR);
+#endif
+
+	return 0;
+}