bpf: Add bpf_trace_vprintk helper

This helper is meant to be "bpf_trace_printk, but with proper vararg
support". Follow bpf_snprintf's example and take a u64 pseudo-vararg
array. Write to /sys/kernel/debug/tracing/trace_pipe using the same
mechanism as bpf_trace_printk. The functionality of this helper was
requested in the libbpf issue tracker [0].

[0] Closes: https://github.com/libbpf/libbpf/issues/315

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-4-davemarchevsky@fb.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index be8d57e..b6c45a6 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1088,6 +1088,7 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *f
 int bpf_prog_calc_tag(struct bpf_prog *fp);
 
 const struct bpf_func_proto *bpf_get_trace_printk_proto(void);
+const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void);
 
 typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
                                        unsigned long off, unsigned long len);

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3e9785f..98ca79a 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4898,6 +4898,16 @@ union bpf_attr {
  *             **-EINVAL** if *flags* is not zero.
  *
  *             **-ENOENT** if architecture does not support branch records.
+ *
+ * long bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data, u32 data_len)
+ *     Description
+ *             Behaves like **bpf_trace_printk**\ () helper, but takes an array of u64
+ *             to format and can handle more format args as a result.
+ *
+ *             Arguments are to be used as in **bpf_seq_printf**\ () helper.
+ *     Return
+ *             The number of bytes written to the buffer, or a negative error
+ *             in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5077,6 +5087,7 @@ union bpf_attr {
        FN(get_attach_cookie),          \
        FN(task_pt_regs),               \
        FN(get_branch_snapshot),        \
+       FN(trace_vprintk),              \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9f4636d..6fddc13 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2357,6 +2357,11 @@ const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
        return NULL;
 }
 
+const struct bpf_func_proto * __weak bpf_get_trace_vprintk_proto(void)
+{
+       return NULL;
+}
+
 u64 __weak
 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
                 void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8f9f392..2c604ff 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1435,6 +1435,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
                return &bpf_snprintf_proto;
        case BPF_FUNC_task_pt_regs:
                return &bpf_task_pt_regs_proto;
+       case BPF_FUNC_trace_vprintk:
+               return bpf_get_trace_vprintk_proto();
        default:
                return NULL;
        }

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4ec779f..6b31538 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -398,7 +398,7 @@ static const struct bpf_func_proto bpf_trace_printk_proto = {
        .arg2_type      = ARG_CONST_SIZE,
 };
 
-const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
+static void __set_printk_clr_event(void)
 {
        /*
         * This program might be calling bpf_trace_printk,
@@ -410,10 +410,58 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
         */
        if (trace_set_clr_event("bpf_trace", "bpf_trace_printk", 1))
                pr_warn_ratelimited("could not enable bpf_trace_printk events");
+}
 
+const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
+{
+       __set_printk_clr_event();
        return &bpf_trace_printk_proto;
 }
 
+BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, data,
+          u32, data_len)
+{
+       static char buf[BPF_TRACE_PRINTK_SIZE];
+       unsigned long flags;
+       int ret, num_args;
+       u32 *bin_args;
+
+       if (data_len & 7 || data_len > MAX_BPRINTF_VARARGS * 8 ||
+           (data_len && !data))
+               return -EINVAL;
+       num_args = data_len / 8;
+
+       ret = bpf_bprintf_prepare(fmt, fmt_size, data, &bin_args, num_args);
+       if (ret < 0)
+               return ret;
+
+       raw_spin_lock_irqsave(&trace_printk_lock, flags);
+       ret = bstr_printf(buf, sizeof(buf), fmt, bin_args);
+
+       trace_bpf_trace_printk(buf);
+       raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
+
+       bpf_bprintf_cleanup();
+
+       return ret;
+}
+
+static const struct bpf_func_proto bpf_trace_vprintk_proto = {
+       .func           = bpf_trace_vprintk,
+       .gpl_only       = true,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_MEM,
+       .arg2_type      = ARG_CONST_SIZE,
+       .arg3_type      = ARG_PTR_TO_MEM_OR_NULL,
+       .arg4_type      = ARG_CONST_SIZE_OR_ZERO,
+};
+
+const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void)
+{
+       __set_printk_clr_event();
+       return &bpf_trace_vprintk_proto;
+}
+
 BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
           const void *, data, u32, data_len)
 {
@@ -1160,6 +1208,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
                return &bpf_get_func_ip_proto_tracing;
        case BPF_FUNC_get_branch_snapshot:
                return &bpf_get_branch_snapshot_proto;
+       case BPF_FUNC_trace_vprintk:
+               return bpf_get_trace_vprintk_proto();
        default:
                return bpf_base_func_proto(func_id);
        }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 3e9785f..98ca79a 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4898,6 +4898,16 @@ union bpf_attr {
  *             **-EINVAL** if *flags* is not zero.
  *
  *             **-ENOENT** if architecture does not support branch records.
+ *
+ * long bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data, u32 data_len)
+ *     Description
+ *             Behaves like **bpf_trace_printk**\ () helper, but takes an array of u64
+ *             to format and can handle more format args as a result.
+ *
+ *             Arguments are to be used as in **bpf_seq_printf**\ () helper.
+ *     Return
+ *             The number of bytes written to the buffer, or a negative error
+ *             in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5077,6 +5087,7 @@ union bpf_attr {
        FN(get_attach_cookie),          \
        FN(task_pt_regs),               \
        FN(get_branch_snapshot),        \
+       FN(trace_vprintk),              \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper