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 <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/net/bpf_jit64.h

@@ -39,10 +39,10 @@
 #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[] = {
@@ -62,6 +62,7 @@ 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

@@ -974,21 +974,37 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	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;
+	if (addrs == NULL) {
+		fp = org_fp;
+		goto out;
+	}
+
+	memset(&cgctx, 0, sizeof(struct codegen_context));
 
-	cgctx.idx = 0;
-	cgctx.seen = 0;
 	/* Scouting faux-generate pass 0 */
-	if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
+	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
@@ -1003,8 +1019,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 
 	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);
 
@@ -1041,6 +1059,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 
 out:
 	kfree(addrs);
+
+	if (bpf_blinded)
+		bpf_jit_prog_release_other(fp, fp == org_fp ? tmp_fp : org_fp);
+
 	return fp;
 }