linux-kernel - Re: [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG

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Message-ID: <20200225175544.GA1385238@rani.riverdale.lan>
Date:   Tue, 25 Feb 2020 12:55:46 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        arjan@...ux.intel.com, keescook@...omium.org,
        rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 05/11] x86: Makefile: Add build and config option for
 CONFIG_FG_KASLR

On Wed, Feb 05, 2020 at 02:39:44PM -0800, Kristen Carlson Accardi wrote:
> Allow user to select CONFIG_FG_KASLR if dependencies are met. Change
> the make file to build with -ffunction-sections if CONFIG_FG_KASLR
> 
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> ---
>  Makefile         |  4 ++++
>  arch/x86/Kconfig | 13 +++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index c50ef91f6136..41438a921666 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -846,6 +846,10 @@ ifdef CONFIG_LIVEPATCH
>  KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone)
>  endif
>  
> +ifdef CONFIG_FG_KASLR
> +KBUILD_CFLAGS += -ffunction-sections
> +endif
> +

With -ffunction-sections I get a few unreachable code warnings from
objtool.

arch/x86/kernel/dumpstack.o: warning: objtool: show_iret_regs()+0x10: unreachable instruction
fs/sysfs/dir.o: warning: objtool: sysfs_create_mount_point()+0x4f: unreachable instruction
kernel/time/clocksource.o: warning: objtool: __clocksource_register_scale()+0x21: unreachable instruction
drivers/tty/sysrq.o: warning: objtool: sysrq_filter()+0x2ef: unreachable instruction
arch/x86/mm/fault.o: warning: objtool: pgtable_bad()+0x3f: unreachable instruction
drivers/acpi/pci_root.o: warning: objtool: acpi_pci_osc_control_set()+0x123: unreachable instruction
drivers/rtc/class.o: warning: objtool: devm_rtc_device_register()+0x40: unreachable instruction
kernel/power/process.o: warning: objtool: freeze_processes.cold()+0x0: unreachable instruction
drivers/pnp/quirks.o: warning: objtool: quirk_awe32_resources()+0x42: unreachable instruction
drivers/acpi/utils.o: warning: objtool: acpi_evaluate_dsm()+0xf1: unreachable instruction
kernel/reboot.o: warning: objtool: __do_sys_reboot()+0x1b6: unreachable instruction
kernel/power/swap.o: warning: objtool: swsusp_read()+0x185: unreachable instruction
drivers/hid/hid-core.o: warning: objtool: hid_hw_start()+0x38: unreachable instruction
drivers/acpi/battery.o: warning: objtool: sysfs_add_battery.cold()+0x1a: unreachable instruction
arch/x86/kernel/cpu/mce/core.o: warning: objtool: do_machine_check.cold()+0x33: unreachable instruction
drivers/pcmcia/cistpl.o: warning: objtool: pccard_store_cis()+0x4e: unreachable instruction
drivers/gpu/vga/vgaarb.o: warning: objtool: pci_notify()+0x35: unreachable instruction
arch/x86/kernel/tsc.o: warning: objtool: determine_cpu_tsc_frequencies()+0x45: unreachable instruction
drivers/pcmcia/yenta_socket.o: warning: objtool: ti1250_override()+0x50: unreachable instruction
fs/proc/proc_sysctl.o: warning: objtool: sysctl_print_dir.isra.0()+0x19: unreachable instruction
drivers/iommu/intel-iommu.o: warning: objtool: intel_iommu_init()+0x4f4: unreachable instruction
net/mac80211/ibss.o: warning: objtool: ieee80211_ibss_work.cold()+0x157: unreachable instruction
drivers/net/ethernet/intel/e1000/e1000_main.o: warning: objtool: e1000_clean.cold()+0x0: unreachable instruction
net/core/skbuff.o: warning: objtool: skb_dump.cold()+0x3fd: unreachable instruction