Re: [PATCHv2 2/2] extract early boot entropy from the passed cmdline

[Kees Cook]

On Wed, Aug 16, 2017 at 3:46 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> From: Daniel Micay <danielmicay@xxxxxxxxx>
>
> Existing Android bootloaders usually pass data useful as early entropy
> on the kernel command-line. It may also be the case on other embedded
> systems. Sample command-line from a Google Pixel running CopperheadOS:
>
>     console=ttyHSL0,115200,n8 androidboot.console=ttyHSL0
>     androidboot.hardware=sailfish user_debug=31 ehci-hcd.park=3
>     lpm_levels.sleep_disabled=1 cma=32M@0-0xffffffff buildvariant=user
>     veritykeyid=id:dfcb9db0089e5b3b4090a592415c28e1cb4545ab
>     androidboot.bootdevice=624000.ufshc androidboot.verifiedbootstate=yellow
>     androidboot.veritymode=enforcing androidboot.keymaster=1
>     androidboot.serialno=FA6CE0305299 androidboot.baseband=msm
>     mdss_mdp.panel=1:dsi:0:qcom,mdss_dsi_samsung_ea8064tg_1080p_cmd:1:none:cfg:single_dsi
>     androidboot.slot_suffix=_b fpsimd.fpsimd_settings=0
>     app_setting.use_app_setting=0 kernelflag=0x00000000 debugflag=0x00000000
>     androidboot.hardware.revision=PVT radioflag=0x00000000
>     radioflagex1=0x00000000 radioflagex2=0x00000000 cpumask=0x00000000
>     androidboot.hardware.ddr=4096MB,Hynix,LPDDR4 androidboot.ddrinfo=00000006
>     androidboot.ddrsize=4GB androidboot.hardware.color=GRA00
>     androidboot.hardware.ufs=32GB,Samsung androidboot.msm.hw_ver_id=268824801
>     androidboot.qf.st=2 androidboot.cid=11111111 androidboot.mid=G-2PW4100
>     androidboot.bootloader=8996-012001-1704121145
>     androidboot.oem_unlock_support=1 androidboot.fp_src=1
>     androidboot.htc.hrdump=detected androidboot.ramdump.opt=mem@2g:2g,mem@4g:2g
>     androidboot.bootreason=reboot androidboot.ramdump_enable=0 ro
>     root=/dev/dm-0 dm="system none ro,0 1 android-verity /dev/sda34"
>     rootwait skip_initramfs init=/init androidboot.wificountrycode=US
>     androidboot.boottime=1BLL:85,1BLE:669,2BLL:0,2BLE:1777,SW:6,KL:8136
>
> Among other things, it contains a value unique to the device
> (androidboot.serialno=FA6CE0305299), unique to the OS builds for the
> device variant (veritykeyid=id:dfcb9db0089e5b3b4090a592415c28e1cb4545ab)
> and timings from the bootloader stages in milliseconds
> (androidboot.boottime=1BLL:85,1BLE:669,2BLL:0,2BLE:1777,SW:6,KL:8136).
>
> Signed-off-by: Daniel Micay <danielmicay@xxxxxxxxx>
> [labbott: Line-wrapped command line]
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
>  init/main.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/init/main.c b/init/main.c
> index 21d599eaad06..cb051aec46ef 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -533,6 +533,7 @@ asmlinkage __visible void __init start_kernel(void)
>          */
>         add_latent_entropy();
>         boot_init_stack_canary();
> +       add_device_randomness(command_line, strlen(command_line));

This should be above the add_latent_entropy() line there so the
cmdline entropy can contribute to the canary entropy.

-Kees

>         mm_init_cpumask(&init_mm);
>         setup_command_line(command_line);
>         setup_nr_cpu_ids();
> --
> 2.13.0
>



-- 
Kees Cook
Pixel Security