Thread (17 messages) 17 messages, 3 authors, 2021-08-24

Re: [PATCH bpf-next 2/5] bpf: add bpf_trace_vprintk helper

From: Andrii Nakryiko <hidden>
Date: 2021-08-24 04:50:59
Also in: bpf, linux-kselftest

On Fri, Aug 20, 2021 at 7:59 PM Dave Marchevsky [off-list ref] wrote:
This helper is meant to be "bpf_trace_printk, but with proper vararg
We have bpf_snprintf() and bpf_seq_printf() names for other BPF
helpers using the same approach. How about we call this one simply
`bpf_printf`? It will be in line with other naming, it is logical BPF
equivalent of user-space printf (which outputs to stderr, which in BPF
land is /sys/kernel/debug/tracing/trace_pipe). And it will be logical
to have a nice and short BPF_PRINTF() convenience macro provided by
libbpf.
support". Follow bpf_snprintf's example and take a u64 pseudo-vararg
array. Write to dmesg using the same mechanism as bpf_trace_printk.
Are you sure about the dmesg part?... bpf_trace_printk is outputting
into /sys/kernel/debug/tracing/trace_pipe.
quoted hunk ↗ jump to hunk
Signed-off-by: Dave Marchevsky <redacted>
---
 include/linux/bpf.h            |  1 +
 include/uapi/linux/bpf.h       | 23 +++++++++++++++
 kernel/bpf/core.c              |  5 ++++
 kernel/bpf/helpers.c           |  2 ++
 kernel/trace/bpf_trace.c       | 52 +++++++++++++++++++++++++++++++++-
 tools/include/uapi/linux/bpf.h | 23 +++++++++++++++
 6 files changed, 105 insertions(+), 1 deletion(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index be8d57e6e78a..b6c45a6cbbba 100644
--- 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 c4f7892edb2b..899a2649d986 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4871,6 +4871,28 @@ union bpf_attr {
  *     Return
  *             Value specified by user at BPF link creation/attachment time
  *             or 0, if it was not specified.
+ *
+ * u64 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. Supports up to 12 arguments to print in this way.
we didn't specify 12 in the description of bpf_snprintf() or
bpf_seq_printf(), so why start doing that here? For data/args format,
let's just refer to bpf_snprintf() or bpf_seq_printf(), whichever does
a better job explaining this :)

+ *             The *fmt* and *fmt_size* are for the format string itself. The *data* and
+ *             *data_len* are format string arguments.
+ *
+ *             Each format specifier in **fmt** corresponds to one u64 element
+ *             in the **data** array. For strings and pointers where pointees
+ *             are accessed, only the pointer values are stored in the *data*
+ *             array. The *data_len* is the size of *data* in bytes.
+ *             Formats **%s**, **%p{i,I}{4,6}** requires to read kernel memory.
+ *             Reading kernel memory may fail due to either invalid address or
+ *             valid address but requiring a major memory fault. If reading kernel memory
+ *             fails, the string for **%s** will be an empty string, and the ip
+ *             address for **%p{i,I}{4,6}** will be 0. Not returning error to
+ *             bpf program is consistent with what **bpf_trace_printk**\ () does for now.
This is just a copy/paste from other helpers. Let's avoid duplication
and just point people to a description in other helpers.
quoted hunk ↗ jump to hunk
+ *
+ *     Return
+ *             The number of bytes written to the buffer, or a negative error
+ *             in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5048,6 +5070,7 @@ union bpf_attr {
        FN(timer_cancel),               \
        FN(get_func_ip),                \
        FN(get_attach_cookie),          \
+       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 91f24c7b38a1..a137c550046c 100644
--- 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 5ce19b376ef7..863e5ee68558 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1419,6 +1419,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
                return &bpf_snprintf_btf_proto;
        case BPF_FUNC_snprintf:
                return &bpf_snprintf_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 2cf4bfa1ab7b..8b3f1ec9e082 100644
--- 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 __always_inline void __set_printk_clr_event(void)
Please drop __always_inline, we only use __always_inline for
absolutely performance critical routines. Let the compiler decide.
quoted hunk ↗ jump to hunk
 {
        /*
         * 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)
 {
@@ -1113,6 +1161,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
                return &bpf_snprintf_proto;
        case BPF_FUNC_get_func_ip:
                return &bpf_get_func_ip_proto_tracing;
+       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 c4f7892edb2b..899a2649d986 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4871,6 +4871,28 @@ union bpf_attr {
  *     Return
  *             Value specified by user at BPF link creation/attachment time
  *             or 0, if it was not specified.
+ *
+ * u64 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. Supports up to 12 arguments to print in this way.
+ *             The *fmt* and *fmt_size* are for the format string itself. The *data* and
+ *             *data_len* are format string arguments.
+ *
+ *             Each format specifier in **fmt** corresponds to one u64 element
+ *             in the **data** array. For strings and pointers where pointees
+ *             are accessed, only the pointer values are stored in the *data*
+ *             array. The *data_len* is the size of *data* in bytes.
+ *             Formats **%s**, **%p{i,I}{4,6}** requires to read kernel memory.
+ *             Reading kernel memory may fail due to either invalid address or
+ *             valid address but requiring a major memory fault. If reading kernel memory
+ *             fails, the string for **%s** will be an empty string, and the ip
+ *             address for **%p{i,I}{4,6}** will be 0. Not returning error to
+ *             bpf program is consistent with what **bpf_trace_printk**\ () does for now.
+ *
+ *     Return
+ *             The number of bytes written to the buffer, or a negative error
+ *             in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5048,6 +5070,7 @@ union bpf_attr {
        FN(timer_cancel),               \
        FN(get_func_ip),                \
        FN(get_attach_cookie),          \
+       FN(trace_vprintk),              \
        /* */

 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.30.2
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