NetBSD Problem Report #57701

From www@netbsd.org  Sat Nov 18 03:47:38 2023
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	for <gnats-bugs@gnats.NetBSD.org>; Sat, 18 Nov 2023 03:47:37 +0000 (UTC)
Message-Id: <20231118034736.9F8271A9239@mollari.NetBSD.org>
Date: Sat, 18 Nov 2023 03:47:36 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: alpha kernel is built with RWX segment
X-Send-Pr-Version: www-1.0

>Number:         57701
>Category:       port-alpha
>Synopsis:       alpha kernel is built with RWX segment
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-alpha-maintainer
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Nov 18 03:50:00 +0000 2023
>Closed-Date:    Sat Nov 18 14:04:42 +0000 2023
>Last-Modified:  Sat Nov 18 14:04:42 +0000 2023
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD LDation
>Environment:
>Description:
/space/tools/bin/../lib/gcc/alpha--netbsd/10.5.0/../../../../alpha--netbsd/bin/ld: warning: cc1 has a LOAD segment with RWX permissions

The kernel image should have finer-grained permissions so the CPU doesn't allow, e.g., writing to the text segment.
>How-To-Repeat:
link an alpha kernel
>Fix:
Teach sys/arch/alpha/conf/kern.ldscript to use separate program segments for read/execute, read/write, and read-only parts of the kernel.

>Release-Note:

>Audit-Trail:
From: Taylor R Campbell <riastradh@NetBSD.org>
To: gnats-bugs@NetBSD.org
Cc: thorpej@NetBSD.org
Subject: Re: port-alpha/57701: alpha kernel is built with RWX segment
Date: Sat, 18 Nov 2023 03:53:37 +0000

 This is a multi-part message in MIME format.
 --=_fvz4bw6Sgb7EvIjKFB6Nr1oMeWUc8Daj

 Attached draft patch attempts to fix this -- not yet compile-tested.

 --=_fvz4bw6Sgb7EvIjKFB6Nr1oMeWUc8Daj
 Content-Type: text/plain; charset="ISO-8859-1"; name="alpharwxldscript"
 Content-Transfer-Encoding: quoted-printable
 Content-Disposition: attachment; filename="alpharwxldscript.patch"

 From b1662f8a75d78b3a04afd0f967561f8c5d8e4412 Mon Sep 17 00:00:00 2001
 From: Taylor R Campbell <riastradh@NetBSD.org>
 Date: Sat, 18 Nov 2023 03:45:01 +0000
 Subject: [PATCH] alpha: Split kernel into RX, R-only, and RW segments.

 PR port-alpha/57701

 XXX pullup-10
 XXX pullup-9
 ---
  sys/arch/alpha/conf/kern.ldscript | 23 +++++++++++++++--------
  1 file changed, 15 insertions(+), 8 deletions(-)

 diff --git a/sys/arch/alpha/conf/kern.ldscript b/sys/arch/alpha/conf/kern.l=
 dscript
 index 1f14867634c3..e403140d73fc 100644
 --- a/sys/arch/alpha/conf/kern.ldscript
 +++ b/sys/arch/alpha/conf/kern.ldscript
 @@ -20,14 +20,14 @@ SECTIONS
  		*(.text)
  		*(.text.*)
  		*(.stub)
 -	} =3D0x47ff041f
 +	} :rxmain =3D0x47ff041f
  	_etext =3D . ;
  	PROVIDE (etext =3D .);
 =20
  	.rodata	:
  	{
  		*(.rodata .rodata.*)
 -	}
 +	} :romain
 =20
  	.data	:
  	{
 @@ -41,7 +41,7 @@ SECTIONS
 =20
  		. =3D ALIGN(COHERENCY_UNIT);
  		*(.data.*)
 -	}
 +	} :rwmain
 =20
  	/*
  	 * Small-data located along side GOT and small-bss for
 @@ -51,12 +51,12 @@ SECTIONS
  	.got	:
  	{
  		*(.got)
 -	}
 +	} :rwmain
 =20
  	.sdata	:
  	{
  		*(.sdata .sdata.*)
 -	}
 +	} :rwmain
  	_edata =3D . ;
  	PROVIDE (edata =3D .) ;
 =20
 @@ -66,13 +66,13 @@ SECTIONS
  	{
  		*(.sbss .sbss.*)
  		*(.scommon)
 -	}
 +	} :rwmain
 =20
  	.bss	:
  	{
  		*(.bss .bss.*)
  		*(COMMON)
 -	}
 +	} :rwmain
 =20
  	/* End of the kernel image */
  	__kernel_end =3D . ;
 @@ -82,5 +82,12 @@ SECTIONS
  	.note.netbsd.ident :
  	{
  		KEEP(*(.note.netbsd.ident));
 -	}
 +	} :romain
 +}
 +
 +PHDRS
 +{
 +	rxmain PT_LOAD;
 +	romain PT_LOAD;
 +	rwmain PT_LOAD;
  }

 --=_fvz4bw6Sgb7EvIjKFB6Nr1oMeWUc8Daj--

From: Jason Thorpe <thorpej@me.com>
To: Taylor Campbell <riastradh@netbsd.org>, gnats-bugs@netbsd.org
Cc: port-alpha-maintainer@netbsd.org, gnats-admin@netbsd.org,
 netbsd-bugs@netbsd.org
Subject: Re: port-alpha/57701: alpha kernel is built with RWX segment
Date: Fri, 17 Nov 2023 21:11:36 -0800

 Alpha loads the kernel into K0SEG and executes it from there, so it doesn=E2=
 =80=99t really matter.

 -- thorpej
 Sent from my iPhone.

 > On Nov 17, 2023, at 7:50=E2=80=AFPM, campbell+netbsd@mumble.net wrote:
 >=20
 > The kernel image should have finer-grained permissions so the CPU doesn't a=
 llow, e.g., writing to the text segment.

From: Jason Thorpe <thorpej@me.com>
To: gnats-bugs@netbsd.org
Cc: port-alpha-maintainer@netbsd.org,
 gnats-admin@netbsd.org,
 netbsd-bugs@netbsd.org
Subject: Re: port-alpha/57701: alpha kernel is built with RWX segment
Date: Sat, 18 Nov 2023 04:57:12 -0800

 Sorry, I responded from my phone last night, and wanted to add some =
 additional context from a proper keyboard.

 > On Nov 17, 2023, at 7:50 PM, campbell+netbsd@mumble.net wrote:
 >=20
 >> Description:
 > =
 /space/tools/bin/../lib/gcc/alpha--netbsd/10.5.0/../../../../alpha--netbsd=
 /bin/ld: warning: cc1 has a LOAD segment with RWX permissions

 Notice my comment was about =E2=80=9Ccc1=E2=80=9D, i.e. the C compiler =
 back-end.  Not about the kernel.

 > The kernel image should have finer-grained permissions so the CPU =
 doesn't allow, e.g., writing to the text segment.

 Doing this for the kernel image would be mostly just a waste of memory, =
 because the kernel is loaded into and executed from K0SEG, which is a =
 direct-mapped segment with no permission enforcement other than =E2=80=9Cn=
 ot accessible from user mode".  The likelihood of *that* being changed =
 is zero, so there=E2=80=99s no point in adding space between the =
 sections to page-align them.

 -- thorpej

State-Changed-From-To: open->closed
State-Changed-By: riastradh@NetBSD.org
State-Changed-When: Sat, 18 Nov 2023 14:04:42 +0000
State-Changed-Why:
derp


>Unformatted:

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