bpf, mips: Implement DADDI workarounds for JIT

For DADDI errata we just workaround by disable immediate operation
for BPF_ADD / BPF_SUB to avoid generation of DADDIU.

All other use cases in JIT won't cause overflow thus they are all safe.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Link: https://lore.kernel.org/bpf/20230228113305.83751-2-jiaxun.yang@flygoat.com

arch/mips/Kconfig

@@ -64,7 +64,6 @@ config MIPS
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_EBPF_JIT if !CPU_MICROMIPS && \
-				!CPU_DADDI_WORKAROUNDS && \
 				!CPU_R4000_WORKAROUNDS && \
 				!CPU_R4400_WORKAROUNDS
 	select HAVE_EXIT_THREAD

arch/mips/net/bpf_jit_comp.c

@@ -218,9 +218,13 @@ bool valid_alu_i(u8 op, s32 imm)
 		/* All legal eBPF values are valid */
 		return true;
 	case BPF_ADD:
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
 		/* imm must be 16 bits */
 		return imm >= -0x8000 && imm <= 0x7fff;
 	case BPF_SUB:
+		if (IS_ENABLED(CONFIG_CPU_DADDI_WORKAROUNDS))
+			return false;
 		/* -imm must be 16 bits */
 		return imm >= -0x7fff && imm <= 0x8000;
 	case BPF_AND: