bpf, x86: save/restore regs with BPF_DW size

[ Upstream commit 02a6dfa ]

As we already reserve 8 byte in the stack for each reg, it is ok to
store/restore the regs in BPF_DW size. This will make the code in
save_regs()/restore_regs() simpler.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230713040738.1789742-2-imagedong@tencent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Stable-dep-of: 2b5dcb3 ("bpf, x64: Fix tailcall infinite loop")
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -1755,57 +1755,34 @@ st:			if (is_imm8(insn->off))
 static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
 		      int stack_size)
 {
-	int i, j, arg_size;
-	bool next_same_struct = false;
+	int i;
 
 	/* Store function arguments to stack.
 	 * For a function that accepts two pointers the sequence will be:
 	 * mov QWORD PTR [rbp-0x10],rdi
 	 * mov QWORD PTR [rbp-0x8],rsi
 	 */
-	for (i = 0, j = 0; i < min(nr_regs, 6); i++) {
-		/* The arg_size is at most 16 bytes, enforced by the verifier. */
-		arg_size = m->arg_size[j];
-		if (arg_size > 8) {
-			arg_size = 8;
-			next_same_struct = !next_same_struct;
-		}
-
-		emit_stx(prog, bytes_to_bpf_size(arg_size),
-			 BPF_REG_FP,
+	for (i = 0; i < min(nr_regs, 6); i++)
+		emit_stx(prog, BPF_DW, BPF_REG_FP,
 			 i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
 			 -(stack_size - i * 8));
-
-		j = next_same_struct ? j : j + 1;
-	}
 }
 
 static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
 			 int stack_size)
 {
-	int i, j, arg_size;
-	bool next_same_struct = false;
+	int i;
 
 	/* Restore function arguments from stack.
 	 * For a function that accepts two pointers the sequence will be:
 	 * EMIT4(0x48, 0x8B, 0x7D, 0xF0); mov rdi,QWORD PTR [rbp-0x10]
 	 * EMIT4(0x48, 0x8B, 0x75, 0xF8); mov rsi,QWORD PTR [rbp-0x8]
 	 */
-	for (i = 0, j = 0; i < min(nr_regs, 6); i++) {
-		/* The arg_size is at most 16 bytes, enforced by the verifier. */
-		arg_size = m->arg_size[j];
-		if (arg_size > 8) {
-			arg_size = 8;
-			next_same_struct = !next_same_struct;
-		}
-
-		emit_ldx(prog, bytes_to_bpf_size(arg_size),
+	for (i = 0; i < min(nr_regs, 6); i++)
+		emit_ldx(prog, BPF_DW,
 			 i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
 			 BPF_REG_FP,
 			 -(stack_size - i * 8));
-
-		j = next_same_struct ? j : j + 1;
-	}
 }
 
 static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,