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[RFC,bpf-next,seccomp,11/12] bpf/verifier: support NULL-able ptr to BTF ID as helper argument

Message ID ca047abace1883f3db0ae009173e3b811085d3e0.1620499942.git.yifeifz2@illinois.edu (mailing list archive)
State New, archived
Headers show
Series eBPF seccomp filters | expand

Commit Message

YiFei Zhu May 10, 2021, 5:22 p.m. UTC 
From: YiFei Zhu <yifeifz2@illinois.edu>

This is to allow progs with no access to ptr to BPF ID still be
able to call some helpers, with these arguments set as NULL, so
the helper implementation may set a fallback when NULL is passed in.

Signed-off-by: YiFei Zhu <yifeifz2@illinois.edu>
---
 include/linux/bpf.h   |  1 +
 kernel/bpf/verifier.c | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)
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Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2019c0893250..efa6444b88d3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -303,6 +303,7 @@  enum bpf_arg_type {
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
 	ARG_PTR_TO_SOCKET_OR_NULL,	/* pointer to bpf_sock (fullsock) or NULL */
 	ARG_PTR_TO_BTF_ID,	/* pointer to in-kernel struct */
+	ARG_PTR_TO_BTF_ID_OR_NULL,	/* pointer to in-kernel struct or NULL */
 	ARG_PTR_TO_ALLOC_MEM,	/* pointer to dynamically allocated memory */
 	ARG_PTR_TO_ALLOC_MEM_OR_NULL,	/* pointer to dynamically allocated memory or NULL */
 	ARG_CONST_ALLOC_SIZE_OR_ZERO,	/* number of allocated bytes requested */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8eec1796caaa..8a08a27e0abc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -484,7 +484,8 @@  static bool arg_type_may_be_null(enum bpf_arg_type type)
 	       type == ARG_PTR_TO_CTX_OR_NULL ||
 	       type == ARG_PTR_TO_SOCKET_OR_NULL ||
 	       type == ARG_PTR_TO_ALLOC_MEM_OR_NULL ||
-	       type == ARG_PTR_TO_STACK_OR_NULL;
+	       type == ARG_PTR_TO_STACK_OR_NULL ||
+	       type == ARG_PTR_TO_BTF_ID_OR_NULL;
 }
 
 /* Determine whether the function releases some resources allocated by another
@@ -4808,6 +4809,7 @@  static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 	[ARG_PTR_TO_SOCKET]		= &fullsock_types,
 	[ARG_PTR_TO_SOCKET_OR_NULL]	= &fullsock_types,
 	[ARG_PTR_TO_BTF_ID]		= &btf_ptr_types,
+	[ARG_PTR_TO_BTF_ID_OR_NULL]	= &btf_ptr_types,
 	[ARG_PTR_TO_SPIN_LOCK]		= &spin_lock_types,
 	[ARG_PTR_TO_MEM]		= &mem_types,
 	[ARG_PTR_TO_MEM_OR_NULL]	= &mem_types,
@@ -5436,10 +5438,14 @@  static bool check_btf_id_ok(const struct bpf_func_proto *fn)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
-		if (fn->arg_type[i] == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])
+		if ((fn->arg_type[i] == ARG_PTR_TO_BTF_ID ||
+		     fn->arg_type[i] == ARG_PTR_TO_BTF_ID_OR_NULL) &&
+		    !fn->arg_btf_id[i])
 			return false;
 
-		if (fn->arg_type[i] != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i])
+		if ((fn->arg_type[i] != ARG_PTR_TO_BTF_ID &&
+		     fn->arg_type[i] != ARG_PTR_TO_BTF_ID_OR_NULL) &&
+		    fn->arg_btf_id[i])
 			return false;
 	}