From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Mon, 23 Apr 2018 14:31:36 +0200
Subject: s390: use expoline thunks in the BPF JIT
Git-commit: de5cb6eb514ebe241e3edeb290cb41deb380b81d
Patch-mainline: v4.17-rc6
References: git-fixes, bsc#1103421
The BPF JIT need safe guarding against spectre v2 in the sk_load_xxx
assembler stubs and the indirect branches generated by the JIT itself
need to be converted to expolines.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
arch/s390/net/bpf_jit.S | 16 ++++++-----
arch/s390/net/bpf_jit_comp.c | 63 ++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 71 insertions(+), 8 deletions(-)
diff --git a/arch/s390/net/bpf_jit.S b/arch/s390/net/bpf_jit.S
index 25bb4643c4f4..9f794869c1b0 100644
--- a/arch/s390/net/bpf_jit.S
+++ b/arch/s390/net/bpf_jit.S
@@ -9,6 +9,7 @@
*/
#include <linux/linkage.h>
+#include <asm/nospec-insn.h>
#include "bpf_jit.h"
/*
@@ -54,7 +55,7 @@ ENTRY(sk_load_##NAME##_pos); \
clg %r3,STK_OFF_HLEN(%r15); /* Offset + SIZE > hlen? */ \
jh sk_load_##NAME##_slow; \
LOAD %r14,-SIZE(%r3,%r12); /* Get data from skb */ \
- b OFF_OK(%r6); /* Return */ \
+ B_EX OFF_OK,%r6; /* Return */ \
\
sk_load_##NAME##_slow:; \
lgr %r2,%r7; /* Arg1 = skb pointer */ \
@@ -64,11 +65,14 @@ sk_load_##NAME##_slow:; \
brasl %r14,skb_copy_bits; /* Get data from skb */ \
LOAD %r14,STK_OFF_TMP(%r15); /* Load from temp bufffer */ \
ltgr %r2,%r2; /* Set cc to (%r2 != 0) */ \
- br %r6; /* Return */
+ BR_EX %r6; /* Return */
sk_load_common(word, 4, llgf) /* r14 = *(u32 *) (skb->data+offset) */
sk_load_common(half, 2, llgh) /* r14 = *(u16 *) (skb->data+offset) */
+ GEN_BR_THUNK %r6
+ GEN_B_THUNK OFF_OK,%r6
+
/*
* Load 1 byte from SKB (optimized version)
*/
@@ -80,7 +84,7 @@ ENTRY(sk_load_byte_pos)
clg %r3,STK_OFF_HLEN(%r15) # Offset >= hlen?
jnl sk_load_byte_slow
llgc %r14,0(%r3,%r12) # Get byte from skb
- b OFF_OK(%r6) # Return OK
+ B_EX OFF_OK,%r6 # Return OK
sk_load_byte_slow:
lgr %r2,%r7 # Arg1 = skb pointer
@@ -90,7 +94,7 @@ sk_load_byte_slow:
brasl %r14,skb_copy_bits # Get data from skb
llgc %r14,STK_OFF_TMP(%r15) # Load result from temp buffer
ltgr %r2,%r2 # Set cc to (%r2 != 0)
- br %r6 # Return cc
+ BR_EX %r6 # Return cc
#define sk_negative_common(NAME, SIZE, LOAD) \
sk_load_##NAME##_slow_neg:; \
@@ -104,7 +108,7 @@ sk_load_##NAME##_slow_neg:; \
jz bpf_error; \
LOAD %r14,0(%r2); /* Get data from pointer */ \
xr %r3,%r3; /* Set cc to zero */ \
- br %r6; /* Return cc */
+ BR_EX %r6; /* Return cc */
sk_negative_common(word, 4, llgf)
sk_negative_common(half, 2, llgh)
@@ -113,4 +117,4 @@ sk_negative_common(byte, 1, llgc)
bpf_error:
# force a return 0 from jit handler
ltgr %r15,%r15 # Set condition code
- br %r6
+ BR_EX %r6
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 78a19c93b380..dd2bcf0e7d00 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -25,6 +25,8 @@
#include <linux/bpf.h>
#include <asm/cacheflush.h>
#include <asm/dis.h>
+#include <asm/facility.h>
+#include <asm/nospec-branch.h>
#include <asm/set_memory.h>
#include "bpf_jit.h"
@@ -41,6 +43,8 @@ struct bpf_jit {
int base_ip; /* Base address for literal pool */
int ret0_ip; /* Address of return 0 */
int exit_ip; /* Address of exit */
+ int r1_thunk_ip; /* Address of expoline thunk for 'br %r1' */
+ int r14_thunk_ip; /* Address of expoline thunk for 'br %r14' */
int tail_call_start; /* Tail call start offset */
int labels[1]; /* Labels for local jumps */
};
@@ -250,6 +254,19 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
REG_SET_SEEN(b2); \
})
+#define EMIT6_PCREL_RILB(op, b, target) \
+({ \
+ int rel = (target - jit->prg) / 2; \
+ _EMIT6(op | reg_high(b) << 16 | rel >> 16, rel & 0xffff); \
+ REG_SET_SEEN(b); \
+})
+
+#define EMIT6_PCREL_RIL(op, target) \
+({ \
+ int rel = (target - jit->prg) / 2; \
+ _EMIT6(op | rel >> 16, rel & 0xffff); \
+})
+
#define _EMIT6_IMM(op, imm) \
({ \
unsigned int __imm = (imm); \
@@ -469,8 +486,45 @@ static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth)
EMIT4(0xb9040000, REG_2, BPF_REG_0);
/* Restore registers */
save_restore_regs(jit, REGS_RESTORE, stack_depth);
+ if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable) {
+ jit->r14_thunk_ip = jit->prg;
+ /* Generate __s390_indirect_jump_r14 thunk */
+ if (test_facility(35)) {
+ /* exrl %r0,.+10 */
+ EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
+ } else {
+ /* larl %r1,.+14 */
+ EMIT6_PCREL_RILB(0xc0000000, REG_1, jit->prg + 14);
+ /* ex 0,0(%r1) */
+ EMIT4_DISP(0x44000000, REG_0, REG_1, 0);
+ }
+ /* j . */
+ EMIT4_PCREL(0xa7f40000, 0);
+ }
/* br %r14 */
_EMIT2(0x07fe);
+
+ if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable &&
+ (jit->seen & SEEN_FUNC)) {
+ jit->r1_thunk_ip = jit->prg;
+ /* Generate __s390_indirect_jump_r1 thunk */
+ if (test_facility(35)) {
+ /* exrl %r0,.+10 */
+ EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
+ /* j . */
+ EMIT4_PCREL(0xa7f40000, 0);
+ /* br %r1 */
+ _EMIT2(0x07f1);
+ } else {
+ /* larl %r1,.+14 */
+ EMIT6_PCREL_RILB(0xc0000000, REG_1, jit->prg + 14);
+ /* ex 0,S390_lowcore.br_r1_tampoline */
+ EMIT4_DISP(0x44000000, REG_0, REG_0,
+ offsetof(struct lowcore, br_r1_trampoline));
+ /* j . */
+ EMIT4_PCREL(0xa7f40000, 0);
+ }
+ }
}
/*
@@ -966,8 +1020,13 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
/* lg %w1,<d(imm)>(%l) */
EMIT6_DISP_LH(0xe3000000, 0x0004, REG_W1, REG_0, REG_L,
EMIT_CONST_U64(func));
- /* basr %r14,%w1 */
- EMIT2(0x0d00, REG_14, REG_W1);
+ if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable) {
+ /* brasl %r14,__s390_indirect_jump_r1 */
+ EMIT6_PCREL_RILB(0xc0050000, REG_14, jit->r1_thunk_ip);
+ } else {
+ /* basr %r14,%w1 */
+ EMIT2(0x0d00, REG_14, REG_W1);
+ }
/* lgr %b0,%r2: load return value into %b0 */
EMIT4(0xb9040000, BPF_REG_0, REG_2);
if ((jit->seen & SEEN_SKB) &&