With the default SPEC_STORE_BYPASS_SECCOMP/SPEC_STORE_BYPASS_PRCTL mode,
the TIF_SSBD bit will be inherited when a new task is fork'ed or cloned.
It will also remain when a new program is execve'ed.
Only certain class of applications (like Java) that can run on behalf of
multiple users on a single thread will require disabling speculative store
bypass for security purposes. Those applications will call prctl(2) at
startup time to disable SSB. They won't rely on the fact the SSB might have
been disabled. Other applications that don't need SSBD will just move on
without checking if SSBD has been turned on or not.
The fact that the TIF_SSBD is inherited across execve(2) boundary will
cause performance of applications that don't need SSBD but their
predecessors have SSBD on to be unwittingly impacted especially if they
write to memory a lot.
To remedy this problem, a new PR_SPEC_DISABLE_NOEXEC argument for the
PR_SET_SPECULATION_CTRL option of prctl(2) is added to allow applications
to specify that the SSBD feature bit on the task structure should be
cleared whenever a new program is being execve'ed.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Link: https://lkml.kernel.org/r/1547676096-3281-1-git-send-email-longman@redhat.com
To pick up changes from:
$ git log --oneline -2 -i include/uapi/linux/prctl.h
356e4bfff2 prctl: Add force disable speculation
b617cfc858 prctl: Add speculation control prctls
$ tools/perf/trace/beauty/prctl_option.sh > before.c
$ cp include/uapi/linux/prctl.h tools/include/uapi/linux/prctl.h
$ tools/perf/trace/beauty/prctl_option.sh > after.c
$ diff -u before.c after.c
--- before.c 2018-06-01 10:39:53.834073962 -0300
+++ after.c 2018-06-01 10:42:11.307985394 -0300
@@ -35,6 +35,8 @@
[42] = "GET_THP_DISABLE",
[45] = "SET_FP_MODE",
[46] = "GET_FP_MODE",
+ [52] = "GET_SPECULATION_CTRL",
+ [53] = "SET_SPECULATION_CTRL",
};
static const char *prctl_set_mm_options[] = {
[1] = "START_CODE",
$
This will be used by 'perf trace' to show these strings when beautifying
the prctl syscall args. At some point we'll be able to say something
like:
'perf trace --all-cpus -e prctl(option=*SPEC*)'
To filter by arg by name.
This silences this warning when building tools/perf:
Warning: Kernel ABI header at 'tools/include/uapi/linux/prctl.h' differs from latest version at 'include/uapi/linux/prctl.h'
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-zztsptwhc264r8wg44tqh5gp@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
To pick up changes from:
2d2123bc7c ("arm64/sve: Add prctl controls for userspace vector length management")
7582e22038 ("arm64/sve: Backend logic for setting the vector length")
That showed a limitation of the regexp used in tools/perf/trace/beauty/prctl_option.sh,
that matches only PR_{SET,GET}_, but should match a few more, like
PR_MPX_*, PR_CAP_* and the one added by the above commit, PR_SVE_SET_*.
This silences this warning when building tools/perf:
Warning: Kernel ABI header at 'tools/include/uapi/linux/prctl.h' differs from latest version at 'include/uapi/linux/prctl.h'
Support for those extra prctl options should be left for the next merge
window tho.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/n/tip-r52dsyuzy04qzqyfcifjs35t@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
