powerpc/bpf: Add support for bpf constant blinding

In line with similar support for other architectures by Daniel Borkmann.

'MOD Default X' from test_bpf without constant blinding:
84 bytes emitted from JIT compiler (pass:3, flen:7)
d0000000058a4688 + <x>:
0: nop
4: nop
8: std r27,-40(r1)
c: std r28,-32(r1)
10: xor r8,r8,r8
14: xor r28,r28,r28
18: mr r27,r3
1c: li r8,66
20: cmpwi r28,0
24: bne 0x0000000000000030
28: li r8,0
2c: b 0x0000000000000044
30: divwu r9,r8,r28
34: mullw r9,r28,r9
38: subf r8,r9,r8
3c: rotlwi r8,r8,0
40: li r8,66
44: ld r27,-40(r1)
48: ld r28,-32(r1)
4c: mr r3,r8
50: blr

... and with constant blinding:
140 bytes emitted from JIT compiler (pass:3, flen:11)
d00000000bd6ab24 + <x>:
0: nop
4: nop
8: std r27,-40(r1)
c: std r28,-32(r1)
10: xor r8,r8,r8
14: xor r28,r28,r28
18: mr r27,r3
1c: lis r2,-22834
20: ori r2,r2,36083
24: rotlwi r2,r2,0
28: xori r2,r2,36017
2c: xoris r2,r2,42702
30: rotlwi r2,r2,0
34: mr r8,r2
38: rotlwi r8,r8,0
3c: cmpwi r28,0
40: bne 0x000000000000004c
44: li r8,0
48: b 0x000000000000007c
4c: divwu r9,r8,r28
50: mullw r9,r28,r9
54: subf r8,r9,r8
58: rotlwi r8,r8,0
5c: lis r2,-17137
60: ori r2,r2,39065
64: rotlwi r2,r2,0
68: xori r2,r2,39131
6c: xoris r2,r2,48399
70: rotlwi r2,r2,0
74: mr r8,r2
78: rotlwi r8,r8,0
7c: ld r27,-40(r1)
80: ld r28,-32(r1)
84: mr r3,r8
88: blr

Signed-off-by: Naveen N. Rao <[e-mail]>
Acked-by: Daniel Borkmann <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/net/bpf_jit64.h

···
 #ifndef __ASSEMBLY__
 
 /* BPF register usage */
-#define SKB_HLEN_REG	(MAX_BPF_REG + 0)
-#define SKB_DATA_REG	(MAX_BPF_REG + 1)
-#define TMP_REG_1	(MAX_BPF_REG + 2)
-#define TMP_REG_2	(MAX_BPF_REG + 3)
+#define SKB_HLEN_REG	(MAX_BPF_JIT_REG + 0)
+#define SKB_DATA_REG	(MAX_BPF_JIT_REG + 1)
+#define TMP_REG_1	(MAX_BPF_JIT_REG + 2)
+#define TMP_REG_2	(MAX_BPF_JIT_REG + 3)
 
 /* BPF to ppc register mappings */
 static const int b2p[] = {
···
 	/* frame pointer aka BPF_REG_10 */
 	[BPF_REG_FP] = 31,
 	/* eBPF jit internal registers */
+	[BPF_REG_AX] = 2,
 	[SKB_HLEN_REG] = 25,
 	[SKB_DATA_REG] = 26,
 	[TMP_REG_1] = 9,

arch/powerpc/net/bpf_jit_comp64.c

···
 	int pass;
 	int flen;
 	struct bpf_binary_header *bpf_hdr;
+	struct bpf_prog *org_fp = fp;
+	struct bpf_prog *tmp_fp;
+	bool bpf_blinded = false;
 
 	if (!bpf_jit_enable)
-		return fp;
+		return org_fp;
+
+	tmp_fp = bpf_jit_blind_constants(org_fp);
+	if (IS_ERR(tmp_fp))
+		return org_fp;
+
+	if (tmp_fp != org_fp) {
+		bpf_blinded = true;
+		fp = tmp_fp;
+	}
 
 	flen = fp->len;
 	addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
-	if (addrs == NULL)
-		return fp;
-
-	cgctx.idx = 0;
-	cgctx.seen = 0;
-	/* Scouting faux-generate pass 0 */
-	if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
-		/* We hit something illegal or unsupported. */
+	if (addrs == NULL) {
+		fp = org_fp;
 		goto out;
+	}
+
+	memset(&cgctx, 0, sizeof(struct codegen_context));
+
+	/* Scouting faux-generate pass 0 */
+	if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
+		/* We hit something illegal or unsupported. */
+		fp = org_fp;
+		goto out;
+	}
 
 	/*
 	 * Pretend to build prologue, given the features we've seen.  This will
···
 
 	bpf_hdr = bpf_jit_binary_alloc(alloclen, &image, 4,
 			bpf_jit_fill_ill_insns);
-	if (!bpf_hdr)
+	if (!bpf_hdr) {
+		fp = org_fp;
 		goto out;
+	}
 
 	code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
 
···
 
 out:
 	kfree(addrs);
+
+	if (bpf_blinded)
+		bpf_jit_prog_release_other(fp, fp == org_fp ? tmp_fp : org_fp);
+
 	return fp;
 }