bpf: Support new unconditional bswap instruction

The existing 'be' and 'le' insns will do conditional bswap
depends on host endianness. This patch implements
unconditional bswap insns.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011213.3712808-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Yonghong Song

arch/x86/net/bpf_jit_comp.c

@@ -1322,6 +1322,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
 			break;
 
 		case BPF_ALU | BPF_END | BPF_FROM_BE:
+		case BPF_ALU64 | BPF_END | BPF_FROM_LE:
 			switch (imm32) {
 			case 16:
 				/* Emit 'ror %ax, 8' to swap lower 2 bytes */

kernel/bpf/core.c

@@ -1524,6 +1524,7 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
 	INSN_3(ALU64, DIV,  X),			\
 	INSN_3(ALU64, MOD,  X),			\
 	INSN_2(ALU64, NEG),			\
+	INSN_3(ALU64, END, TO_LE),		\
 	/*   Immediate based. */		\
 	INSN_3(ALU64, ADD,  K),			\
 	INSN_3(ALU64, SUB,  K),			\
@@ -1848,6 +1849,19 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 			break;
 		}
 		CONT;
+	ALU64_END_TO_LE:
+		switch (IMM) {
+		case 16:
+			DST = (__force u16) __swab16(DST);
+			break;
+		case 32:
+			DST = (__force u32) __swab32(DST);
+			break;
+		case 64:
+			DST = (__force u64) __swab64(DST);
+			break;
+		}
+		CONT;
 
 	/* CALL */
 	JMP_CALL:

kernel/bpf/verifier.c

@@ -3012,8 +3012,10 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		}
 	}
 
+	if (class == BPF_ALU64 && op == BPF_END && (insn->imm == 16 || insn->imm == 32))
+		return false;
+
 	if (class == BPF_ALU64 || class == BPF_JMP ||
-	    /* BPF_END always use BPF_ALU class. */
 	    (class == BPF_ALU && op == BPF_END && insn->imm == 64))
 		return true;
 
@@ -13076,7 +13078,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 		} else {
 			if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
 			    (insn->imm != 16 && insn->imm != 32 && insn->imm != 64) ||
-			    BPF_CLASS(insn->code) == BPF_ALU64) {
+			    (BPF_CLASS(insn->code) == BPF_ALU64 &&
+			     BPF_SRC(insn->code) != BPF_TO_LE)) {
 				verbose(env, "BPF_END uses reserved fields\n");
 				return -EINVAL;
 			}