* [PATCH 0/2] Proper ro_after_init implementation on s390
@ 2016-06-07 12:06 Heiko Carstens
2016-06-07 15:49 ` Kees Cook
0 siblings, 1 reply; 6+ messages in thread
From: Heiko Carstens @ 2016-06-07 12:06 UTC (permalink / raw)
To: Kees Cook, Ingo Molnar; +Cc: Martin Schwidefsky, linux-kernel
These two patches allow a proper ro_after_init implementation on s390.
The current implementation maps __ro_after_init to __read_mostly,
which means that ro_after_init data won't be write protected at all.
Reason for this is that s390 write protects rodata very early (before
init calls) and therefore adding ro_after_init data to rodata would
lead to crashes.
Since I don't want to mark the page table entries much later read-only
on s390 just to make this work, allow an architecture specific
handling which can be used to move the ro_after_init data to a
different place which can be marked read-only later when
mark_rodata_ro gets executed.
Note: these patches require the s390 kernel page table splitting
support which currently is only available at
git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git features
(included in linux-next)
Therefore, if we can agree on this solution I'd like to add these
patches to the s390 tree, so it can be merged during the next merge
window.
Heiko Carstens (2):
vmlinux.lds.h: allow arch specific handling of ro_after_init data section
s390/mm: add proper __ro_after_init support
arch/s390/include/asm/cache.h | 3 ---
arch/s390/include/asm/sections.h | 1 +
arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
arch/s390/mm/init.c | 7 ++++---
arch/s390/mm/vmem.c | 7 +++----
include/asm-generic/vmlinux.lds.h | 10 +++++++++-
6 files changed, 28 insertions(+), 12 deletions(-)
--
2.6.6
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] Proper ro_after_init implementation on s390
2016-06-07 12:06 [PATCH 0/2] Proper ro_after_init implementation on s390 Heiko Carstens
@ 2016-06-07 15:49 ` Kees Cook
2016-06-07 18:07 ` Heiko Carstens
0 siblings, 1 reply; 6+ messages in thread
From: Kees Cook @ 2016-06-07 15:49 UTC (permalink / raw)
To: Heiko Carstens; +Cc: Ingo Molnar, Martin Schwidefsky, LKML
On Tue, Jun 7, 2016 at 5:06 AM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> These two patches allow a proper ro_after_init implementation on s390.
>
> The current implementation maps __ro_after_init to __read_mostly,
> which means that ro_after_init data won't be write protected at all.
>
> Reason for this is that s390 write protects rodata very early (before
> init calls) and therefore adding ro_after_init data to rodata would
> lead to crashes.
>
> Since I don't want to mark the page table entries much later read-only
> on s390 just to make this work, allow an architecture specific
> handling which can be used to move the ro_after_init data to a
> different place which can be marked read-only later when
> mark_rodata_ro gets executed.
>
> Note: these patches require the s390 kernel page table splitting
> support which currently is only available at
>
> git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git features
>
> (included in linux-next)
>
> Therefore, if we can agree on this solution I'd like to add these
> patches to the s390 tree, so it can be merged during the next merge
> window.
>
> Heiko Carstens (2):
> vmlinux.lds.h: allow arch specific handling of ro_after_init data section
> s390/mm: add proper __ro_after_init support
>
> arch/s390/include/asm/cache.h | 3 ---
> arch/s390/include/asm/sections.h | 1 +
> arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
> arch/s390/mm/init.c | 7 ++++---
> arch/s390/mm/vmem.c | 7 +++----
> include/asm-generic/vmlinux.lds.h | 10 +++++++++-
> 6 files changed, 28 insertions(+), 12 deletions(-)
Awesome! This looks great to me! Have you had a chance to look through
any of the arch/s390/ __init code for variables that should be marked
__ro_after_init?
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] Proper ro_after_init implementation on s390
2016-06-07 15:49 ` Kees Cook
@ 2016-06-07 18:07 ` Heiko Carstens
2016-06-07 18:11 ` Kees Cook
0 siblings, 1 reply; 6+ messages in thread
From: Heiko Carstens @ 2016-06-07 18:07 UTC (permalink / raw)
To: Kees Cook; +Cc: Ingo Molnar, Martin Schwidefsky, LKML
On Tue, Jun 07, 2016 at 08:49:14AM -0700, Kees Cook wrote:
> > Heiko Carstens (2):
> > vmlinux.lds.h: allow arch specific handling of ro_after_init data section
> > s390/mm: add proper __ro_after_init support
> >
> > arch/s390/include/asm/cache.h | 3 ---
> > arch/s390/include/asm/sections.h | 1 +
> > arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
> > arch/s390/mm/init.c | 7 ++++---
> > arch/s390/mm/vmem.c | 7 +++----
> > include/asm-generic/vmlinux.lds.h | 10 +++++++++-
> > 6 files changed, 28 insertions(+), 12 deletions(-)
>
> Awesome! This looks great to me! Have you had a chance to look through
> any of the arch/s390/ __init code for variables that should be marked
> __ro_after_init?
Not yet, and actually this I'm a bit reluctant to do that, since any wrong
annotation will lead to kernel crashes sooner or later ;)
However I'll look into this as well.
> Reviewed-by: Kees Cook <keescook@chromium.org>
Thanks! I add that to both patches.
(sorry for the broken threading; one of the outgoing mail servers rewrote
all Message-Id headers)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] Proper ro_after_init implementation on s390
2016-06-07 18:07 ` Heiko Carstens
@ 2016-06-07 18:11 ` Kees Cook
2016-06-08 5:41 ` Heiko Carstens
0 siblings, 1 reply; 6+ messages in thread
From: Kees Cook @ 2016-06-07 18:11 UTC (permalink / raw)
To: Heiko Carstens; +Cc: Ingo Molnar, Martin Schwidefsky, LKML
On Tue, Jun 7, 2016 at 11:07 AM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> On Tue, Jun 07, 2016 at 08:49:14AM -0700, Kees Cook wrote:
>> > Heiko Carstens (2):
>> > vmlinux.lds.h: allow arch specific handling of ro_after_init data section
>> > s390/mm: add proper __ro_after_init support
>> >
>> > arch/s390/include/asm/cache.h | 3 ---
>> > arch/s390/include/asm/sections.h | 1 +
>> > arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
>> > arch/s390/mm/init.c | 7 ++++---
>> > arch/s390/mm/vmem.c | 7 +++----
>> > include/asm-generic/vmlinux.lds.h | 10 +++++++++-
>> > 6 files changed, 28 insertions(+), 12 deletions(-)
>>
>> Awesome! This looks great to me! Have you had a chance to look through
>> any of the arch/s390/ __init code for variables that should be marked
>> __ro_after_init?
>
> Not yet, and actually this I'm a bit reluctant to do that, since any wrong
> annotation will lead to kernel crashes sooner or later ;)
> However I'll look into this as well.
Yup, though the good news is it's usually discovered very quickly. :)
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>
> Thanks! I add that to both patches.
>
> (sorry for the broken threading; one of the outgoing mail servers rewrote
> all Message-Id headers)
Cool, no worries. I tried to reply to what looked like the right one. :)
-Kees
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] Proper ro_after_init implementation on s390
2016-06-07 18:11 ` Kees Cook
@ 2016-06-08 5:41 ` Heiko Carstens
2016-06-08 15:49 ` Kees Cook
0 siblings, 1 reply; 6+ messages in thread
From: Heiko Carstens @ 2016-06-08 5:41 UTC (permalink / raw)
To: Kees Cook; +Cc: Ingo Molnar, Martin Schwidefsky, LKML
On Tue, Jun 07, 2016 at 11:11:17AM -0700, Kees Cook wrote:
> On Tue, Jun 7, 2016 at 11:07 AM, Heiko Carstens
> <heiko.carstens@de.ibm.com> wrote:
> > On Tue, Jun 07, 2016 at 08:49:14AM -0700, Kees Cook wrote:
> >> > Heiko Carstens (2):
> >> > vmlinux.lds.h: allow arch specific handling of ro_after_init data section
> >> > s390/mm: add proper __ro_after_init support
> >> >
> >> > arch/s390/include/asm/cache.h | 3 ---
> >> > arch/s390/include/asm/sections.h | 1 +
> >> > arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
> >> > arch/s390/mm/init.c | 7 ++++---
> >> > arch/s390/mm/vmem.c | 7 +++----
> >> > include/asm-generic/vmlinux.lds.h | 10 +++++++++-
> >> > 6 files changed, 28 insertions(+), 12 deletions(-)
> >>
> >> Awesome! This looks great to me! Have you had a chance to look through
> >> any of the arch/s390/ __init code for variables that should be marked
> >> __ro_after_init?
> >
> > Not yet, and actually this I'm a bit reluctant to do that, since any wrong
> > annotation will lead to kernel crashes sooner or later ;)
> > However I'll look into this as well.
>
> Yup, though the good news is it's usually discovered very quickly. :)
Eventually it might make sense to add something like
DEBUG_SECTION_MISMATCH, which would only report on _write_ accesses from
non-init sections.
Not sure if this can be done easily and without the need of a new compiler
feature. The new problem class I'm afraid of is more or less the same that
we had when non-init code referenced (already freed) initdata objects.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] Proper ro_after_init implementation on s390
2016-06-08 5:41 ` Heiko Carstens
@ 2016-06-08 15:49 ` Kees Cook
0 siblings, 0 replies; 6+ messages in thread
From: Kees Cook @ 2016-06-08 15:49 UTC (permalink / raw)
To: Heiko Carstens; +Cc: Ingo Molnar, Martin Schwidefsky, LKML
On Tue, Jun 7, 2016 at 10:41 PM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> On Tue, Jun 07, 2016 at 11:11:17AM -0700, Kees Cook wrote:
>> On Tue, Jun 7, 2016 at 11:07 AM, Heiko Carstens
>> <heiko.carstens@de.ibm.com> wrote:
>> > On Tue, Jun 07, 2016 at 08:49:14AM -0700, Kees Cook wrote:
>> >> > Heiko Carstens (2):
>> >> > vmlinux.lds.h: allow arch specific handling of ro_after_init data section
>> >> > s390/mm: add proper __ro_after_init support
>> >> >
>> >> > arch/s390/include/asm/cache.h | 3 ---
>> >> > arch/s390/include/asm/sections.h | 1 +
>> >> > arch/s390/kernel/vmlinux.lds.S | 12 +++++++++++-
>> >> > arch/s390/mm/init.c | 7 ++++---
>> >> > arch/s390/mm/vmem.c | 7 +++----
>> >> > include/asm-generic/vmlinux.lds.h | 10 +++++++++-
>> >> > 6 files changed, 28 insertions(+), 12 deletions(-)
>> >>
>> >> Awesome! This looks great to me! Have you had a chance to look through
>> >> any of the arch/s390/ __init code for variables that should be marked
>> >> __ro_after_init?
>> >
>> > Not yet, and actually this I'm a bit reluctant to do that, since any wrong
>> > annotation will lead to kernel crashes sooner or later ;)
>> > However I'll look into this as well.
>>
>> Yup, though the good news is it's usually discovered very quickly. :)
>
> Eventually it might make sense to add something like
> DEBUG_SECTION_MISMATCH, which would only report on _write_ accesses from
> non-init sections.
>
> Not sure if this can be done easily and without the need of a new compiler
> feature. The new problem class I'm afraid of is more or less the same that
> we had when non-init code referenced (already freed) initdata objects.
Yeah. I'm hopeful we'll have a gcc plugin to help with this soon.
-Kees
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply [flat|nested] 6+ messages in thread
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2016-06-07 12:06 [PATCH 0/2] Proper ro_after_init implementation on s390 Heiko Carstens
2016-06-07 15:49 ` Kees Cook
2016-06-07 18:07 ` Heiko Carstens
2016-06-07 18:11 ` Kees Cook
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