Revert "bpf: prevent speculative execution in eBPF interpreter"

CVE-2017-5753 (revert embargoed)
CVE-2017-5715 (revert embargoed)

This reverts commit ac92d827.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

kernel/bpf/core.c

@@ -29,7 +29,6 @@
 #include <linux/bpf.h>
 
 #include <asm/unaligned.h>
-#include <asm/barrier.h>
 
 /* Registers */
 #define BPF_R0	regs[BPF_REG_0]
@@ -631,7 +630,6 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 		DST = IMM;
 		CONT;
 	LD_IMM_DW:
-		gmb();
 		DST = (u64) (u32) insn[0].imm | ((u64) (u32) insn[1].imm) << 32;
 		insn++;
 		CONT;
@@ -846,7 +844,6 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 		*(SIZE *)(unsigned long) (DST + insn->off) = IMM;	\
 		CONT;							\
 	LDX_MEM_##SIZEOP:						\
-		gmb();							\
 		DST = *(SIZE *)(unsigned long) (SRC + insn->off);	\
 		CONT;