[PATCH RFC bpf-next 1/4] bpf: add bpf_jhash_mem BPF helper

[Andrii Nakryiko <andrii@kernel.org>]

Add BPF helper that allows to calculate jhash of arbitrary (initialized)
memory slice.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 include/uapi/linux/bpf.h       |  8 ++++++++
 kernel/bpf/helpers.c           | 23 +++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  8 ++++++++
 3 files changed, 39 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2e3048488feb..7b17e46b0be2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4913,6 +4913,13 @@ union bpf_attr {
  *	Return
  *		The number of bytes written to the buffer, or a negative error
  *		in case of failure.
+ *
+ * u64 bpf_jhash_mem(const void *data, u32 sz, u32 seed)
+ *	Description
+ *		Calculate jhash of a given memory slice.
+ *
+ *	Return
+ *		Calculated hash value.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5093,6 +5100,7 @@ union bpf_attr {
 	FN(task_pt_regs),		\
 	FN(get_branch_snapshot),	\
 	FN(trace_vprintk),		\
+	FN(jhash_mem),			\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 2c604ff8c7fb..00fb1b69595c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -15,9 +15,30 @@
 #include <linux/pid_namespace.h>
 #include <linux/proc_ns.h>
 #include <linux/security.h>
+#include <linux/jhash.h>
 
 #include "../../lib/kstrtox.h"
 
+BPF_CALL_3(bpf_jhash_mem, const void *, data, u32, sz, u32, seed)
+{
+	if (unlikely((uintptr_t)data % 4 || sz % 4))
+		return jhash(data, sz, seed);
+
+	/* optimized 4-byte version */
+	return jhash2(data, sz / 4, seed);
+}
+
+
+static const struct bpf_func_proto bpf_jhash_mem_proto = {
+	.func		= bpf_jhash_mem,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
+	.arg3_type	= ARG_ANYTHING,
+};
+
+
 /* If kernel subsystem is allowing eBPF programs to call this function,
  * inside its own verifier_ops->get_func_proto() callback it should return
  * bpf_map_lookup_elem_proto, so that verifier can properly check the arguments
@@ -1341,6 +1362,8 @@ const struct bpf_func_proto *
 bpf_base_func_proto(enum bpf_func_id func_id)
 {
 	switch (func_id) {
+	case BPF_FUNC_jhash_mem:
+		return &bpf_jhash_mem_proto;
 	case BPF_FUNC_map_lookup_elem:
 		return &bpf_map_lookup_elem_proto;
 	case BPF_FUNC_map_update_elem:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2e3048488feb..7b17e46b0be2 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4913,6 +4913,13 @@ union bpf_attr {
  *	Return
  *		The number of bytes written to the buffer, or a negative error
  *		in case of failure.
+ *
+ * u64 bpf_jhash_mem(const void *data, u32 sz, u32 seed)
+ *	Description
+ *		Calculate jhash of a given memory slice.
+ *
+ *	Return
+ *		Calculated hash value.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5093,6 +5100,7 @@ union bpf_attr {
 	FN(task_pt_regs),		\
 	FN(get_branch_snapshot),	\
 	FN(trace_vprintk),		\
+	FN(jhash_mem),			\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.30.2