linux-kernel - [v4.9 PATCH 5/6] init/main.c: extract early boot entropy from the passed cmdline

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Message-Id: <20220731182635.1910069-6-hegtvedt@cisco.com>
Date:   Sun, 31 Jul 2022 20:26:35 +0200
From:   Hans-Christian Noren Egtvedt <hegtvedt@...co.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, Daniel Micay <danielmicay@...il.com>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Laura Abbott <lauraa@...eaurora.org>,
        Nick Kralevich <nnk@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [v4.9 PATCH 5/6] init/main.c: extract early boot entropy from the passed cmdline

From: Daniel Micay <danielmicay@...il.com>

Feed the boot command-line as to the /dev/random entropy pool

Existing Android bootloaders usually pass data which may not be known by
an external attacker 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@...xffffffff 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).

[tytso@....edu: changelog tweak]
[labbott@...hat.com: line-wrapped command line]
Link: http://lkml.kernel.org/r/20170816231458.2299-3-labbott@redhat.com
Signed-off-by: Daniel Micay <danielmicay@...il.com>
Signed-off-by: Laura Abbott <labbott@...hat.com>
Acked-by: Kees Cook <keescook@...omium.org>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Laura Abbott <lauraa@...eaurora.org>
Cc: Nick Kralevich <nnk@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
(cherry picked from commit 33d72f3822d7ff8a9e45bd7413c811085cb87aa5)
---
 init/main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/init/main.c b/init/main.c
index 67fa94c5967..6bc1a3fa152 100644
--- a/init/main.c
+++ b/init/main.c
@@ -502,8 +502,10 @@ asmlinkage __visible void __init start_kernel(void)
 	setup_arch(&command_line);
 	/*
 	 * Set up the the initial canary and entropy after arch
+	 * and after adding latent and command line entropy.
 	 */
 	add_latent_entropy();
+	add_device_randomness(command_line, strlen(command_line));
 	boot_init_stack_canary();
 	mm_init_cpumask(&init_mm);
 	setup_command_line(command_line);
-- 
2.34.1