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s390: use expoline thunks in the BPF JIT

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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>
This commit is contained in:
Martin Schwidefsky 2018-04-23 14:31:36 +02:00
parent 6deaa3bbca
commit de5cb6eb51
2 changed files with 71 additions and 8 deletions
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63
arch/s390/net/bpf_jit_comp.c
View file

@ -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) &&