bpf: add missing header file include

stable inclusion
from stable-v4.19.274
commit c7603df97635954165fb599e64e197efc353979b
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6TIG1
CVE: NA

--------------------------------

commit f3dd0c53 upstream.

Commit 74e19ef0 ("uaccess: Add speculation barrier to
copy_from_user()") built fine on x86-64 and arm64, and that's the extent
of my local build testing.

It turns out those got the <linux/nospec.h> include incidentally through
other header files (<linux/kvm_host.h> in particular), but that was not
true of other architectures, resulting in build errors

  kernel/bpf/core.c: In function ‘___bpf_prog_run’:
  kernel/bpf/core.c:1913:3: error: implicit declaration of function ‘barrier_nospec’

so just make sure to explicitly include the proper <linux/nospec.h>
header file to make everybody see it.

Fixes: 74e19ef0 ("uaccess: Add speculation barrier to copy_from_user()")
Reported-by: Nkernel test robot <lkp@intel.com>
Reported-by: NViresh Kumar <viresh.kumar@linaro.org>
Reported-by: NHuacai Chen <chenhuacai@loongson.cn>
Tested-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Tested-by: NDave Hansen <dave.hansen@linux.intel.com>
Acked-by: NAlexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

kernel/bpf/core.c

@@ -32,6 +32,7 @@
 #include <linux/kallsyms.h>
 #include <linux/rcupdate.h>
 #include <linux/perf_event.h>
+#include <linux/nospec.h>
 
 #include <asm/barrier.h>
 #include <asm/unaligned.h>