net: filter: make register naming more comprehensible

The current code is a bit hard to parse on which registers can be used,
how they are mapped and all play together. It makes much more sense to
define this a bit more clearly so that the code is a bit more intuitive.
This patch cleans this up, and makes naming a bit more consistent among
the code. This also allows for moving some of the defines into the header
file. Clearing of A and X registers in __sk_run_filter() do not get a
particular register name assigned as they have not an 'official' function,
but rather just result from the concrete initial mapping of old BPF
programs. Since for BPF helper functions for BPF_CALL we already use
small letters, so be consistent here as well. No functional changes.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/filter.h

@@ -40,16 +40,47 @@
 /* Placeholder/dummy for 0 */
 #define BPF_0		0
 
+/* Register numbers */
+enum {
+	BPF_REG_0 = 0,
+	BPF_REG_1,
+	BPF_REG_2,
+	BPF_REG_3,
+	BPF_REG_4,
+	BPF_REG_5,
+	BPF_REG_6,
+	BPF_REG_7,
+	BPF_REG_8,
+	BPF_REG_9,
+	BPF_REG_10,
+	__MAX_BPF_REG,
+};
+
 /* BPF has 10 general purpose 64-bit registers and stack frame. */
-#define MAX_BPF_REG	11
+#define MAX_BPF_REG	__MAX_BPF_REG
+
+/* ArgX, context and stack frame pointer register positions. Note,
+ * Arg1, Arg2, Arg3, etc are used as argument mappings of function
+ * calls in BPF_CALL instruction.
+ */
+#define BPF_REG_ARG1	BPF_REG_1
+#define BPF_REG_ARG2	BPF_REG_2
+#define BPF_REG_ARG3	BPF_REG_3
+#define BPF_REG_ARG4	BPF_REG_4
+#define BPF_REG_ARG5	BPF_REG_5
+#define BPF_REG_CTX	BPF_REG_6
+#define BPF_REG_FP	BPF_REG_10
+
+/* Additional register mappings for converted user programs. */
+#define BPF_REG_A	BPF_REG_0
+#define BPF_REG_X	BPF_REG_7
+#define BPF_REG_TMP	BPF_REG_8
 
 /* BPF program can access up to 512 bytes of stack space. */
 #define MAX_BPF_STACK	512
 
-/* Arg1, context and stack frame pointer register positions. */
-#define ARG1_REG	1
-#define CTX_REG		6
-#define FP_REG		10
+/* Macro to invoke filter function. */
+#define SK_RUN_FILTER(filter, ctx)  (*filter->bpf_func)(ctx, filter->insnsi)
 
 struct sock_filter_int {
 	__u8	code;		/* opcode */
@@ -100,9 +131,6 @@ static inline unsigned int sk_filter_size(unsigned int proglen)
 #define sk_filter_proglen(fprog)			\
 		(fprog->len * sizeof(fprog->filter[0]))
 
-#define SK_RUN_FILTER(filter, ctx)			\
-		(*filter->bpf_func)(ctx, filter->insnsi)
-
 int sk_filter(struct sock *sk, struct sk_buff *skb);
 
 u32 sk_run_filter_int_seccomp(const struct seccomp_data *ctx,