Revert "bpf: prevent speculative execution in eBPF interpreter"

This reverts commit 81774d48 which was
part of an out-of-tree mitigation for CVE-2017-5753 (Spectre variant 1),
in the BPF subsystem, that was available at the time of the coordinated
release date. The Ubuntu kernel has since rebased on top of newer
linux-stable releases and picked up commit b2157399 ("bpf: prevent
out-of-bounds speculation") which is upstream's mitigation of Spectre
variant 1 in the BPF code.

CVE-2017-5753
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@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]
@@ -632,7 +631,6 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 		DST = IMM;
 		CONT;
 	LD_IMM_DW:
-		osb();
 		DST = (u64) (u32) insn[0].imm | ((u64) (u32) insn[1].imm) << 32;
 		insn++;
 		CONT;
@@ -847,7 +845,6 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 		*(SIZE *)(unsigned long) (DST + insn->off) = IMM;	\
 		CONT;							\
 	LDX_MEM_##SIZEOP:						\
-		osb();							\
 		DST = *(SIZE *)(unsigned long) (SRC + insn->off);	\
 		CONT;