lkml.org 
[lkml]   [2021]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 34/38] x86/build: Disable CET instrumentation in the kernel
    Date
    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit 20bf2b378729c4a0366a53e2018a0b70ace94bcd upstream.

    With retpolines disabled, some configurations of GCC, and specifically
    the GCC versions 9 and 10 in Ubuntu will add Intel CET instrumentation
    to the kernel by default. That breaks certain tracing scenarios by
    adding a superfluous ENDBR64 instruction before the fentry call, for
    functions which can be called indirectly.

    CET instrumentation isn't currently necessary in the kernel, as CET is
    only supported in user space. Disable it unconditionally and move it
    into the x86's Makefile as CET/CFI... enablement should be a per-arch
    decision anyway.

    [ bp: Massage and extend commit message. ]

    Fixes: 29be86d7f9cb ("kbuild: add -fcf-protection=none when using retpoline flags")
    Reported-by: Nikolay Borisov <nborisov@suse.com>
    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Nikolay Borisov <nborisov@suse.com>
    Tested-by: Nikolay Borisov <nborisov@suse.com>
    Cc: <stable@vger.kernel.org>
    Cc: Seth Forshee <seth.forshee@canonical.com>
    Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
    Link: https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    Makefile | 6 ------
    arch/x86/Makefile | 3 +++
    2 files changed, 3 insertions(+), 6 deletions(-)

    --- a/Makefile
    +++ b/Makefile
    @@ -830,12 +830,6 @@ KBUILD_CFLAGS += $(call cc-option,-Wer
    # Prohibit date/time macros, which would make the build non-deterministic
    KBUILD_CFLAGS += $(call cc-option,-Werror=date-time)

    -# ensure -fcf-protection is disabled when using retpoline as it is
    -# incompatible with -mindirect-branch=thunk-extern
    -ifdef CONFIG_RETPOLINE
    -KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
    -endif
    -
    # use the deterministic mode of AR if available
    KBUILD_ARFLAGS := $(call ar-option,D)

    --- a/arch/x86/Makefile
    +++ b/arch/x86/Makefile
    @@ -137,6 +137,9 @@ else
    KBUILD_CFLAGS += -mno-red-zone
    KBUILD_CFLAGS += -mcmodel=kernel

    + # Intel CET isn't enabled in the kernel
    + KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
    +
    # -funit-at-a-time shrinks the kernel .text considerably
    # unfortunately it makes reading oopses harder.
    KBUILD_CFLAGS += $(call cc-option,-funit-at-a-time)

    \
     
     \ /
      Last update: 2021-02-08 16:26    [W:7.773 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site