bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/rust/helpers/vmalloc.c b/rust/helpers/vmalloc.c
new file mode 100644
index 000000000..6aed13292
--- /dev/null
+++ b/rust/helpers/vmalloc.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+
+__rust_helper void *__must_check __realloc_size(2)
+rust_helper_vrealloc_node_align(const void *p, size_t size, unsigned long align,
+				gfp_t flags, int node)
+{
+	return vrealloc_node_align(p, size, align, flags, node);
+}
+
+__rust_helper bool rust_helper_is_vmalloc_addr(const void *x)
+{
+	return is_vmalloc_addr(x);
+}