powerpc64/bpf: Implement bpf_addr_space_cast instruction

LLVM generates bpf_addr_space_cast instruction while translating
pointers between native (zero) address space and
__attribute__((address_space(N))). The addr_space=0 is reserved as
bpf_arena address space.

rY = addr_space_cast(rX, 0, 1) is processed by the verifier and
converted to normal 32-bit move: wX = wY.

rY = addr_space_cast(rX, 1, 0) : used to convert a bpf arena pointer to
a pointer in the userspace vma. This has to be converted by the JIT.

PPC_RAW_RLDICL_DOT, a variant of PPC_RAW_RLDICL is introduced to set
condition register as well.

Reviewed-by: Hari Bathini <[email protected]>
Tested-by: Venkat Rao Bagalkote <[email protected]>
Signed-off-by: Saket Kumar Bhaskar <[email protected]>

Author: Saket Kumar Bhaskar

arch/powerpc/include/asm/ppc-opcode.h

@@ -571,6 +571,7 @@
 					(0x54000001 | ___PPC_RA(d) | ___PPC_RS(a) | __PPC_SH(i) | __PPC_MB(mb) | __PPC_ME(me))
 #define PPC_RAW_RLWIMI(d, a, i, mb, me) (0x50000000 | ___PPC_RA(d) | ___PPC_RS(a) | __PPC_SH(i) | __PPC_MB(mb) | __PPC_ME(me))
 #define PPC_RAW_RLDICL(d, a, i, mb)     (0x78000000 | ___PPC_RA(d) | ___PPC_RS(a) | __PPC_SH64(i) | __PPC_MB64(mb))
+#define PPC_RAW_RLDICL_DOT(d, a, i, mb) (0x78000000 | ___PPC_RA(d) | ___PPC_RS(a) | __PPC_SH64(i) | __PPC_MB64(mb) | 0x1)
 #define PPC_RAW_RLDICR(d, a, i, me)     (0x78000004 | ___PPC_RA(d) | ___PPC_RS(a) | __PPC_SH64(i) | __PPC_ME64(me))
 
 /* slwi = rlwinm Rx, Ry, n, 0, 31-n */

arch/powerpc/net/bpf_jit.h

@@ -165,6 +165,7 @@ struct codegen_context {
 	unsigned int exentry_idx;
 	unsigned int alt_exit_addr;
 	u64 arena_vm_start;
+	u64 user_vm_start;
 };
 
 #define bpf_to_ppc(r)	(ctx->b2p[r])

arch/powerpc/net/bpf_jit_comp.c

@@ -205,6 +205,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	/* Make sure that the stack is quadword aligned. */
 	cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
 	cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);
+	cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);
 
 	/* Scouting faux-generate pass 0 */
 	if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
@@ -439,6 +440,11 @@ bool bpf_jit_supports_kfunc_call(void)
 	return true;
 }
 
+bool bpf_jit_supports_arena(void)
+{
+	return IS_ENABLED(CONFIG_PPC64);
+}
+
 bool bpf_jit_supports_far_kfunc_call(void)
 {
 	return IS_ENABLED(CONFIG_PPC64);

arch/powerpc/net/bpf_jit_comp64.c

@@ -812,6 +812,16 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		 */
 		case BPF_ALU | BPF_MOV | BPF_X: /* (u32) dst = src */
 		case BPF_ALU64 | BPF_MOV | BPF_X: /* dst = src */
+
+			if (insn_is_cast_user(&insn[i])) {
+				EMIT(PPC_RAW_RLDICL_DOT(tmp1_reg, src_reg, 0, 32));
+				PPC_LI64(dst_reg, (ctx->user_vm_start & 0xffffffff00000000UL));
+				PPC_BCC_SHORT(COND_EQ, (ctx->idx + 2) * 4);
+				EMIT(PPC_RAW_OR(tmp1_reg, dst_reg, tmp1_reg));
+				EMIT(PPC_RAW_MR(dst_reg, tmp1_reg));
+				break;
+			}
+
 			if (imm == 1) {
 				/* special mov32 for zext */
 				EMIT(PPC_RAW_RLWINM(dst_reg, dst_reg, 0, 0, 31));