bpf: Refactor bprintf buffer support

Refactor code to be able to get and put bprintf buffers and use
bpf_printf_prepare independently. This will be used in the next patch to
implement BPF streams support, particularly as a staging buffer for
strings that need to be formatted and then allocated and pushed into a
stream.

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250703204818.925464-2-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 287c956cdbd28a14092109237cced0f1f578d634..a07451457d9e713a599854fde5ddb9eaa3c37734 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3551,6 +3551,16 @@ bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
 #define MAX_BPRINTF_VARARGS            12
 #define MAX_BPRINTF_BUF                        1024
 
+/* Per-cpu temp buffers used by printf-like helpers to store the bprintf binary
+ * arguments representation.
+ */
+#define MAX_BPRINTF_BIN_ARGS   512
+
+struct bpf_bprintf_buffers {
+       char bin_args[MAX_BPRINTF_BIN_ARGS];
+       char buf[MAX_BPRINTF_BUF];
+};
+
 struct bpf_bprintf_data {
        u32 *bin_args;
        char *buf;
@@ -3558,9 +3568,12 @@ struct bpf_bprintf_data {
        bool get_buf;
 };
 
-int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
+int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
                        u32 num_args, struct bpf_bprintf_data *data);
 void bpf_bprintf_cleanup(struct bpf_bprintf_data *data);
+int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs);
+void bpf_put_buffers(void);
+
 
 #ifdef CONFIG_BPF_LSM
 void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype);

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5269381d6d3d3b5413875461d38fa29cdfb97925..da66ce307e75afc17014fadcf4946af9bb6dcde4 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -764,22 +764,13 @@ static int bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
        return -EINVAL;
 }
 
-/* Per-cpu temp buffers used by printf-like helpers to store the bprintf binary
- * arguments representation.
- */
-#define MAX_BPRINTF_BIN_ARGS   512
-
 /* Support executing three nested bprintf helper calls on a given CPU */
 #define MAX_BPRINTF_NEST_LEVEL 3
-struct bpf_bprintf_buffers {
-       char bin_args[MAX_BPRINTF_BIN_ARGS];
-       char buf[MAX_BPRINTF_BUF];
-};
 
 static DEFINE_PER_CPU(struct bpf_bprintf_buffers[MAX_BPRINTF_NEST_LEVEL], bpf_bprintf_bufs);
 static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
 
-static int try_get_buffers(struct bpf_bprintf_buffers **bufs)
+int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs)
 {
        int nest_level;
 
@@ -795,16 +786,21 @@ static int try_get_buffers(struct bpf_bprintf_buffers **bufs)
        return 0;
 }
 
-void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
+void bpf_put_buffers(void)
 {
-       if (!data->bin_args && !data->buf)
-               return;
        if (WARN_ON_ONCE(this_cpu_read(bpf_bprintf_nest_level) == 0))
                return;
        this_cpu_dec(bpf_bprintf_nest_level);
        preempt_enable();
 }
 
+void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
+{
+       if (!data->bin_args && !data->buf)
+               return;
+       bpf_put_buffers();
+}
+
 /*
  * bpf_bprintf_prepare - Generic pass on format strings for bprintf-like helpers
  *
@@ -819,7 +815,7 @@ void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
  * In argument preparation mode, if 0 is returned, safe temporary buffers are
  * allocated and bpf_bprintf_cleanup should be called to free them after use.
  */
-int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
+int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
                        u32 num_args, struct bpf_bprintf_data *data)
 {
        bool get_buffers = (data->get_bin_args && num_args) || data->get_buf;
@@ -835,7 +831,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
                return -EINVAL;
        fmt_size = fmt_end - fmt;
 
-       if (get_buffers && try_get_buffers(&buffers))
+       if (get_buffers && bpf_try_get_buffers(&buffers))
                return -EBUSY;
 
        if (data->get_bin_args) {