A newbie's question

A newbie's question

[immortal1015]

Hi, all. I am a newbie to Linuxe Kernel. I am reading the kernel source about bootstrap in Linux.
I was confused by the boot.s:
/////////////////////////////
   	mov	ax,#BOOTSEG
	mov	ds,ax
	mov	ax,#INITSEG
	mov	es,ax
	mov	cx,#256
	sub	si,si
	sub	di,di
	rep
	movw
	jmpi	go,INITSEG
/////////////////////////////
1. What assembly language used in boot.s? Intel Asm or AT&T?
2. Where is the definition of operand movw and jmpi? I cant find it in the Intel Manual.

Please give me some adivices.

Best regards.

Re: A newbie's question

[jbradford]

> Hi, all. I am a newbie to Linuxe Kernel. I am reading the kernel source about bootstrap in Linux.
> I was confused by the boot.s:
> /////////////////////////////
>    	mov	ax,#BOOTSEG
> 	mov	ds,ax
> 	mov	ax,#INITSEG
> 	mov	es,ax
> 	mov	cx,#256
> 	sub	si,si
> 	sub	di,di
> 	rep
> 	movw
> 	jmpi	go,INITSEG
> /////////////////////////////
> 1. What assembly language used in boot.s? Intel Asm or AT&T?
> 2. Where is the definition of operand movw and jmpi? I cant find it in the Intel Manual.
> 
> Please give me some adivices.

I could be totally wrong here, but my understanding of the situtation is that the bootstrap was originally compiled with as86, not gas, and therefore was in the Intel format, (the standard for gas being AT&T, although Gas can also compile Intel format using the .intel_syntax pseudo-op).  I assume that the bootloader has stayed in Intel format for historical reasons.

However, I could be totally wrong.  The last assembler coding I did was on a Z80 :-).

John.

Re: A newbie's question

[DervishD]

    Hi unknown :)

> 	rep
> 	movw

    In my bootsector.S, it's movsw: repeat move (string) by words.
'movw' is 'mov word size operands'.

> 	jmpi	go,INITSEG

    AFAIK, the correct is 'ljmp': long jump. What kernel sources are
you seeing?. Old kernels (2.0 and I think that 2.2 too) used as86 to
do the assembling, and the syntax was like the Intel one, but with
some differences. Not quite standard, I think.

> /////////////////////////////
> 1. What assembly language used in boot.s? Intel Asm or AT&T?

    AT&T in new kernels, fully 'assembleable' with GNU as. IMHO is a
better syntax, but I don't want to feed a troll here ;)

> 2. Where is the definition of operand movw and jmpi?
> I cant find it in the Intel Manual.

    Of course, there aren't Intel syntax anyway :) I recommend you to
see the 2.4 sources for reading the assembler part. Moreover, the
info section for 'GNU as' comments the differences between Intel
assembly syntax and the AT&T one. This will be of great help.

    In addition to this, I have a document about using GNU as for
real mode assembly that comments some of these points. But it is
written in spanish only :((

    Last, the Assembly-HOWTO will cast some light to the issue, too.

    Raúl

A newbie's question

[David Li]

Hi,

I thought I would post this question here in addition to the Fedora
list to get more help.

----

Maybe this is just for my own clarifications;
I am about to start SELinux learning and development.  I have a stock
Cento 7.1 install and I am curious what''s difference between the
following two:

1. Enable SElinux and setenforce 1 on the stock install

vs.

2. Build a reference policy RPM and install it on the box. Then do
step 1 as above.

Are there any differences in terms of ref policy? Would step 1 also
have the ref policy enabled by default too?

Thanks.

RE: A newbie's question

[Higgs, Stephen]

> -----Original Message-----
> From: Selinux [mailto:selinux-bounces@tycho.nsa.gov] On Behalf Of David
> Li
> Sent: Tuesday, December 08, 2015 1:29 PM
> To: selinux@tycho.nsa.gov
> Subject: A newbie's question
> 
> Hi,
> 
> I thought I would post this question here in addition to the Fedora list
> to get more help.
> 
> ----
> 
> Maybe this is just for my own clarifications; I am about to start
> SELinux learning and development.  I have a stock Cento 7.1 install and
> I am curious what''s difference between the following two:
> 
> 1. Enable SElinux and setenforce 1 on the stock install
> 
> vs.
> 
> 2. Build a reference policy RPM and install it on the box. Then do step
> 1 as above.
> 
> Are there any differences in terms of ref policy? Would step 1 also have
> the ref policy enabled by default too?
> 
> Thanks.
> _______________________________________________
> Selinux mailing list
> Selinux@tycho.nsa.gov
> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> To get help, send an email containing "help" to Selinux-
> request@tycho.nsa.gov.

CentOS 7.1 has the reference policy installed, but there could be a difference in version of the RPM reference policy and the version that is current for 7.1.

The seinfo command is one way to show what is currently installed.

--Stephen

Re: A newbie's question

[David Li]

Hi Stephen,

If I install my own ref policy RPM on the Centos7 box, would that
replace the existing or stock ref policy?

David

On Tue, Dec 8, 2015 at 10:48 AM, Higgs, Stephen <Stephen.Higgs@icfi.com> wrote:
>> -----Original Message-----
>> From: Selinux [mailto:selinux-bounces@tycho.nsa.gov] On Behalf Of David
>> Li
>> Sent: Tuesday, December 08, 2015 1:29 PM
>> To: selinux@tycho.nsa.gov
>> Subject: A newbie's question
>>
>> Hi,
>>
>> I thought I would post this question here in addition to the Fedora list
>> to get more help.
>>
>> ----
>>
>> Maybe this is just for my own clarifications; I am about to start
>> SELinux learning and development.  I have a stock Cento 7.1 install and
>> I am curious what''s difference between the following two:
>>
>> 1. Enable SElinux and setenforce 1 on the stock install
>>
>> vs.
>>
>> 2. Build a reference policy RPM and install it on the box. Then do step
>> 1 as above.
>>
>> Are there any differences in terms of ref policy? Would step 1 also have
>> the ref policy enabled by default too?
>>
>> Thanks.
>> _______________________________________________
>> Selinux mailing list
>> Selinux@tycho.nsa.gov
>> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
>> To get help, send an email containing "help" to Selinux-
>> request@tycho.nsa.gov.
>
> CentOS 7.1 has the reference policy installed, but there could be a difference in version of the RPM reference policy and the version that is current for 7.1.
>
> The seinfo command is one way to show what is currently installed.
>
> --Stephen
>

RE: A newbie's question

[Higgs, Stephen]

I have not installed the ref policy for CentOS, but consider that SELinux policy modules are a great avenue to customize your system.  Maybe you should tell us what you are trying to achieve?

--Stephen


> -----Original Message-----
> From: David Li [mailto:dlipubkey@gmail.com]
> Sent: Friday, December 11, 2015 11:31 AM
> To: Higgs, Stephen
> Cc: selinux@tycho.nsa.gov
> Subject: Re: A newbie's question
> 
> Hi Stephen,
> 
> If I install my own ref policy RPM on the Centos7 box, would that
> replace the existing or stock ref policy?
> 
> David
> 
> On Tue, Dec 8, 2015 at 10:48 AM, Higgs, Stephen <Stephen.Higgs@icfi.com>
> wrote:
> >> -----Original Message-----
> >> From: Selinux [mailto:selinux-bounces@tycho.nsa.gov] On Behalf Of
> >> David Li
> >> Sent: Tuesday, December 08, 2015 1:29 PM
> >> To: selinux@tycho.nsa.gov
> >> Subject: A newbie's question
> >>
> >> Hi,
> >>
> >> I thought I would post this question here in addition to the Fedora
> >> list to get more help.
> >>
> >> ----
> >>
> >> Maybe this is just for my own clarifications; I am about to start
> >> SELinux learning and development.  I have a stock Cento 7.1 install
> >> and I am curious what''s difference between the following two:
> >>
> >> 1. Enable SElinux and setenforce 1 on the stock install
> >>
> >> vs.
> >>
> >> 2. Build a reference policy RPM and install it on the box. Then do
> >> step
> >> 1 as above.
> >>
> >> Are there any differences in terms of ref policy? Would step 1 also
> >> have the ref policy enabled by default too?
> >>
> >> Thanks.
> >> _______________________________________________
> >> Selinux mailing list
> >> Selinux@tycho.nsa.gov
> >> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> >> To get help, send an email containing "help" to Selinux-
> >> request@tycho.nsa.gov.
> >
> > CentOS 7.1 has the reference policy installed, but there could be a
> difference in version of the RPM reference policy and the version that
> is current for 7.1.
> >
> > The seinfo command is one way to show what is currently installed.
> >
> > --Stephen
> >

Re: A newbie's question

[David Li]

Hi Stephen,

My goal is to study how to use SElinux policy for an application
running on Centos. My approach is to build everything into one single
RPM for easy installation/upgrade/change. This includes both the ref
policy and application policy. I started out by building the RPM with
only ref policy. I will add in app policy after I make sure this RPM
works well.

David


On Fri, Dec 11, 2015 at 9:07 AM, Higgs, Stephen <Stephen.Higgs@icfi.com> wrote:
> I have not installed the ref policy for CentOS, but consider that SELinux policy modules are a great avenue to customize your system.  Maybe you should tell us what you are trying to achieve?
>
> --Stephen
>
>
>> -----Original Message-----
>> From: David Li [mailto:dlipubkey@gmail.com]
>> Sent: Friday, December 11, 2015 11:31 AM
>> To: Higgs, Stephen
>> Cc: selinux@tycho.nsa.gov
>> Subject: Re: A newbie's question
>>
>> Hi Stephen,
>>
>> If I install my own ref policy RPM on the Centos7 box, would that
>> replace the existing or stock ref policy?
>>
>> David
>>
>> On Tue, Dec 8, 2015 at 10:48 AM, Higgs, Stephen <Stephen.Higgs@icfi.com>
>> wrote:
>> >> -----Original Message-----
>> >> From: Selinux [mailto:selinux-bounces@tycho.nsa.gov] On Behalf Of
>> >> David Li
>> >> Sent: Tuesday, December 08, 2015 1:29 PM
>> >> To: selinux@tycho.nsa.gov
>> >> Subject: A newbie's question
>> >>
>> >> Hi,
>> >>
>> >> I thought I would post this question here in addition to the Fedora
>> >> list to get more help.
>> >>
>> >> ----
>> >>
>> >> Maybe this is just for my own clarifications; I am about to start
>> >> SELinux learning and development.  I have a stock Cento 7.1 install
>> >> and I am curious what''s difference between the following two:
>> >>
>> >> 1. Enable SElinux and setenforce 1 on the stock install
>> >>
>> >> vs.
>> >>
>> >> 2. Build a reference policy RPM and install it on the box. Then do
>> >> step
>> >> 1 as above.
>> >>
>> >> Are there any differences in terms of ref policy? Would step 1 also
>> >> have the ref policy enabled by default too?
>> >>
>> >> Thanks.
>> >> _______________________________________________
>> >> Selinux mailing list
>> >> Selinux@tycho.nsa.gov
>> >> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
>> >> To get help, send an email containing "help" to Selinux-
>> >> request@tycho.nsa.gov.
>> >
>> > CentOS 7.1 has the reference policy installed, but there could be a
>> difference in version of the RPM reference policy and the version that
>> is current for 7.1.
>> >
>> > The seinfo command is one way to show what is currently installed.
>> >
>> > --Stephen
>> >