[PATCH v5 bpf-next 1/9] bpf: Expose bpf_dynptr_slice* kfuncs for in kernel use

Song Liu
2023-10-24T06:31:11Z

kfuncs bpf_dynptr_slice and bpf_dynptr_slice_rdwr are used by BPF programs
to access the dynptr data. They are also useful for in kernel functions
that access dynptr data, for example, bpf_verify_pkcs7_signature.

Add bpf_dynptr_slice and bpf_dynptr_slice_rdwr to bpf.h so that kernel
functions can use them instead of accessing dynptr->data directly.

Update bpf_verify_pkcs7_signature to use bpf_dynptr_slice instead of
dynptr->data.

Also, update the comments for bpf_dynptr_slice and bpf_dynptr_slice_rdwr
that they may return error pointers for BPF_DYNPTR_TYPE_XDP.

Signed-off-by: Song Liu <song@kernel.org>
---
include/linux/bpf.h | 4 ++++
kernel/bpf/helpers.c | 16 ++++++++--------
kernel/trace/bpf_trace.c | 15 +++++++++++----
3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b4825d3cdb29..3ed3ae37cbdf 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1222,6 +1222,10 @@ enum bpf_dynptr_type {

int bpf_dynptr_check_size(u32 size);
u32 __bpf_dynptr_size(const struct bpf_dynptr_kern *ptr);
+void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset,
+ void *buffer__opt, u32 buffer__szk);
+void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr_kern *ptr, u32 offset,
+ void *buffer__opt, u32 buffer__szk);

#ifdef CONFIG_BPF_JIT
int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e46ac288a108..af5059f11e83 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2270,10 +2270,10 @@ __bpf_kfunc struct task_struct *bpf_task_from_pid(s32 pid)
* bpf_dynptr_slice will not invalidate any ctx->data/data_end pointers in
* the bpf program.
*
- * Return: NULL if the call failed (eg invalid dynptr), pointer to a read-only
- * data slice (can be either direct pointer to the data or a pointer to the user
- * provided buffer, with its contents containing the data, if unable to obtain
- * direct pointer)
+ * Return: NULL or error pointer if the call failed (eg invalid dynptr), pointer
+ * to a read-only data slice (can be either direct pointer to the data or a
+ * pointer to the user provided buffer, with its contents containing the data,
+ * if unable to obtain direct pointer)
*/
__bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset,
void *buffer__opt, u32 buffer__szk)
@@ -2354,10 +2354,10 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset
* bpf_dynptr_slice_rdwr will not invalidate any ctx->data/data_end pointers in
* the bpf program.
*
- * Return: NULL if the call failed (eg invalid dynptr), pointer to a
- * data slice (can be either direct pointer to the data or a pointer to the user
- * provided buffer, with its contents containing the data, if unable to obtain
- * direct pointer)
+ * Return: NULL or error pointer if the call failed (eg invalid dynptr), pointer
+ * to a data slice (can be either direct pointer to the data or a pointer to the
+ * user provided buffer, with its contents containing the data, if unable to
+ * obtain direct pointer)
*/
__bpf_kfunc void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr_kern *ptr, u32 offset,
void *buffer__opt, u32 buffer__szk)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index df697c74d519..2626706b6387 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1378,6 +1378,7 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
struct bpf_dynptr_kern *sig_ptr,
struct bpf_key *trusted_keyring)
{
+ void *data, *sig;
int ret;

if (trusted_keyring->has_ref) {
@@ -1394,10 +1395,16 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
return ret;
}

- return verify_pkcs7_signature(data_ptr->data,
- __bpf_dynptr_size(data_ptr),
- sig_ptr->data,
- __bpf_dynptr_size(sig_ptr),
+ data = bpf_dynptr_slice(data_ptr, 0, NULL, 0);
+ if (IS_ERR(data))
+ return PTR_ERR(data);
+
+ sig = bpf_dynptr_slice(sig_ptr, 0, NULL, 0);
+ if (IS_ERR(sig))
+ return PTR_ERR(sig);
+
+ return verify_pkcs7_signature(data, __bpf_dynptr_size(data_ptr),
+ sig, __bpf_dynptr_size(sig_ptr),
trusted_keyring->key,
VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
NULL);
--
2.34.1