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Subject[PATCH 3/3] bpf powerpc: add support for bpf constant blinding
Date
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>
---
arch/powerpc/net/bpf_jit64.h | 9 +++++----
arch/powerpc/net/bpf_jit_comp64.c | 36 +++++++++++++++++++++++++++++-------
2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit64.h b/arch/powerpc/net/bpf_jit64.h
index 038e00b..62fa758 100644
--- a/arch/powerpc/net/bpf_jit64.h
+++ b/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,
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 3ec29d6..0fe98a5 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/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;
}

--
2.9.3
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