linux-kernel - [RFC bpf-next 10/13] bpf: verifier: Add indirection to kallsyms_lookup

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Message-ID: <7540678e9a46c13f680f2aacab28bb88446583f5.1744169424.git.dxu@dxuuu.xyz>
Date: Tue,  8 Apr 2025 21:34:05 -0600
From: Daniel Xu <dxu@...uu.xyz>
To: andrii@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net
Cc: john.fastabend@...il.com,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC bpf-next 10/13] bpf: verifier: Add indirection to kallsyms_lookup_name()

kallsyms_lookup_name() cannot be exported from the kernel for policy
reasons, so add this layer of indirection to allow the verifier to still
do kfunc and global variable relocations.

Signed-off-by: Daniel Xu <dxu@...uu.xyz>
---
 include/linux/bpf.h   |  2 ++
 kernel/bpf/core.c     | 14 ++++++++++++++
 kernel/bpf/verifier.c | 13 +++++--------
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 44133727820d..a5806a7b31d3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2797,6 +2797,8 @@ static inline int kfunc_desc_cmp_by_id_off(const void *a, const void *b)
 }
 const struct bpf_kfunc_desc *
 find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset);
+unsigned long bpf_lookup_type_addr(struct btf *btf, const struct btf_type *func,
+				   const char **name);
 int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
 		       u16 btf_fd_idx, u8 **func_addr);
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e892e469061e..13301a668fe0 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1639,6 +1639,20 @@ find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset)
 }
 EXPORT_SYMBOL_GPL(find_kfunc_desc);
 
+unsigned long bpf_lookup_type_addr(struct btf *btf, const struct btf_type *t,
+				   const char **name)
+{
+	unsigned long addr;
+
+	*name = btf_name_by_offset(btf, t->name_off);
+	addr = kallsyms_lookup_name(*name);
+	if (!addr)
+		return -ENOENT;
+
+	return addr;
+}
+EXPORT_SYMBOL_GPL(bpf_lookup_type_addr);
+
 int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
 		       u16 btf_fd_idx, u8 **func_addr)
 {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7e84df2abe41..080cc380e806 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3131,11 +3131,9 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 		return -EINVAL;
 	}
 
-	func_name = btf_name_by_offset(desc_btf, func->name_off);
-	addr = kallsyms_lookup_name(func_name);
-	if (!addr) {
-		verbose(env, "cannot find address for kernel function %s\n",
-			func_name);
+	addr = bpf_lookup_type_addr(desc_btf, func, &func_name);
+	if (addr < 0) {
+		verbose(env, "cannot find address for kernel function %s\n", func_name);
 		return -EINVAL;
 	}
 	specialize_kfunc(env, func_id, offset, &addr);
@@ -19707,9 +19705,8 @@ static int __check_pseudo_btf_id(struct bpf_verifier_env *env,
 		return -EINVAL;
 	}
 
-	sym_name = btf_name_by_offset(btf, t->name_off);
-	addr = kallsyms_lookup_name(sym_name);
-	if (!addr) {
+	addr = bpf_lookup_type_addr(btf, t, &sym_name);
+	if (addr < 0) {
 		verbose(env, "ldimm64 failed to find the address for kernel symbol '%s'.\n",
 			sym_name);
 		return -ENOENT;
-- 
2.47.1