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([2a01:e34:ec1a:b010:2425:ce29:e778:70f4]) by smtp.gmail.com with ESMTPSA id 8sm2880846wrz.60.2022.01.13.23.21.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Jan 2022 23:31:33 -0800 (PST) In-Reply-To: References: X-Referenced-Uid: 4297 Thread-Topic: Re: How to disable address randomization ? User-Agent: Android X-Is-Generated-Message-Id: true MIME-Version: 1.0 X-Local-Message-Id: Subject: Re: How to disable address randomization ? From: admin LI Date: Fri, 14 Jan 2022 08:12:28 +0100 To: noloader@gmail.com Message-ID: Cc: kernelnewbies X-BeenThere: kernelnewbies@kernelnewbies.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Learn about the Linux kernel List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============7307272848408698409==" Errors-To: kernelnewbies-bounces@kernelnewbies.org --===============7307272848408698409== Content-Type: multipart/alternative; boundary="----QBCAVPBRUR4DAUWQWU8DJ91KE9B30H" Content-Transfer-Encoding: 7bit ------QBCAVPBRUR4DAUWQWU8DJ91KE9B30H Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Hi Jeff, Thanks for your help, finally I found this in kernel document=2E = Pointer Types =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Pointers printed w= ithout a specifier extension (i=2Ee unadorned %p) are hashed to give a uniq= ue identifier without leaking kernel addresses to user space=2E On 64 bit m= achines the first 32 bits are zeroed=2E If you _really_ want the address se= e %px below=2E =E2=81=A3Get BlueMail for Android =E2=80=8B On Jan 13, 202= 2, 23:44, at 23:44, Jeffrey Walton wrote: >On Thu, J= an 13, 2022 at 4:04 PM admin LI wrote: >> >> I'm de= veloping a kernel module for an ARM machine, while debugging I >found addre= sses >> printed are all randomized and useless for debugging=2E >> >> To pr= ove I was not crazy I wrote this small program: >> >> ---------------------= ------------ >> #include >> #include >>= #include >> #include >> >> MODULE_LICE= NSE("GPL"); >> MODULE_AUTHOR("Somebody"); >> MODULE_DESCRIPTION("A simple e= xample Linux module=2E"); >> MODULE_VERSION("0=2E01"); >> >> static int __i= nit example_init(void) { >> uint32_t a; >> uint32_t b; >> uint3= 2_t c; >> uint8_t d[10]; >> uint8_t *e; >> >> printk(KERN_INFO = "Hello, World!\n"); >> printk(KERN_INFO "&a %p\n",&a); >> printk(KE= RN_INFO "&b %p\n",&b); >> printk(KERN_INFO "&c %p\n",&c); >> printk= (KERN_INFO "&d %p\n",d); >> printk(KERN_INFO "&d[0] %p\n",&d[0]); >> = printk(KERN_INFO "&d[1] %p\n",&d[1]); >> >> e =3D kmalloc(10, GFP_KER= NEL); >> printk(KERN_INFO "&e[0] %p\n",&e[0]); >> printk(KERN_INFO = "&e[1] %p\n",&e[1]); >> >> kfree(e); >> >> return 0; >> } >> >> static= void __exit example_exit(void) { >> printk(KERN_INFO "Goodbye, World!\n")= ; >> } >> >> module_init(example_init); >> module_exit(example_exit); >> --= ------------------------------- >> And it gave me this output: >> >> Hello,= World! >> &a b3f9fa31 >> &b 27e1c68a >> &c da50d287 >> &d 9f9aec2b >> &d[0= ] 9f9aec2b >> &d[1] cc627580 >> &e[0] 98b8c9eb >> &e[1] 45f248f8 >> >> Then= I tested on my debian host machine which gave me the same kind >of randomi= zed addresses=2E >> >> When I search randomization the only thing I found i= s KASLR which I >don't think is the same thing=2E > >I think something else= may be going on, but I'll toss this out there >in case it helps=2E > >In t= he past randomization was disabled by writing 0 to >/proc/sys/kernel/random= ize_va_space=2E Something like: > > sysctl -w kernel=2Erandomize_va_spac= e=3D0 > >To make it permanent, change it in /etc/sysctl=2Econf=2E > >Jeff ------QBCAVPBRUR4DAUWQWU8DJ91KE9B30H Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Hi Jeff,
=
Thanks for your help, finally I found this in = kernel document=2E

Pointer Types
=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Pointers printed without a specifier extension (i=2Ee unadorne= d %p) are hashed to give a unique identifier without leaking kernel address= es to user space=2E On 64 bit machines the first 32 bits are zeroed=2E If y= ou _really_ want the address see %px below=2E

On Jan 13, 2022, at 23:44, Jeffrey Walton <noloader@gmail=2Ecom> wrote: 
On Thu, Jan 13, 2022 at 4:04 PM admin LI <admin@hifiphile=2Ecom> w=
rote:

 I'm develo=
ping a kernel module for an ARM machine, while debugging I found addresses<=
br> printed are all randomized and useless for debugging=2E

 To prov=
e I was not crazy I wrote this small program:


 #include <=
linux/init=2Eh>
 #include <linux/module=2Eh>
 #include <l=
inux/kernel=2Eh>
 #include <linux/slab=2Eh>

 MODULE_LICE=
NSE("GPL");
 MODULE_AUTHOR("Somebody");
 MODULE_DESCRIPTION("A simple=
 example Linux module=2E");
 MODULE_VERSION("0=2E01");

 static in=
t __init example_init(void) {
     uint32_t a;
     uint32_t b;
  =
   uint32_t c;
     uint8_t d[10];
     uint8_t *e;

     print=
k(KERN_INFO "Hello, World!\n");
     printk(KERN_INFO "&a %p\n",&=
;a);
     printk(KERN_INFO "&b %p\n",&b);
     printk(KERN_IN=
FO "&c %p\n",&c);
     printk(KERN_INFO "&d %p\n",d);
   =
  printk(KERN_INFO "&d[0] %p\n",&d[0]);
     printk(KERN_INFO "&=
amp;d[1] %p\n",&d[1]);

     e =3D kmalloc(10, GFP_KERNEL);
  =
   printk(KERN_INFO "&e[0] %p\n",&e[0]);
     printk(KERN_INFO "=
&e[1] %p\n",&e[1]);

     kfree(e);

  return 0;
 }<=
br>
 static void __exit example_exit(void) {
  printk(KERN_INFO "Good=
bye, World!\n");
 }

 module_init(example_init);
 module_exit(e=
xample_exit);

 And it gave me this output:

 Hello, World!=

 &a b3f9fa31
 &b 27e1c68a
 &c da50d287
 &d 9f9=
aec2b
 &d[0] 9f9aec2b
 &d[1] cc627580
 &e[0] 98b8c9eb<=
br> &e[1] 45f248f8

 Then I tested on my debian host machine whic=
h gave me the same kind of randomized addresses=2E

 When I search ra=
ndomization the only thing I found is KASLR which I don't think is the same=
 thing=2E

I think something else may be going on, but I=
'll toss this out there
in case it helps=2E

In the past randomiza=
tion was disabled by writing 0 to
/proc/sys/kernel/randomize_va_space=2E=
 Something like:

    sysctl -w kernel=2Erandomize_va_space=3D0
To make it permanent, change it in /etc/sysctl=2Econf=2E

Jeff
<=
/pre>
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