From: Laura Abbott <labbott@redhat.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>,
Laura Abbott <labbott@fedoraproject.org>
Cc: Kees Cook <keescook@chromium.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] arm: Use kernel mm when updating section permissions
Date: Thu, 5 Nov 2015 08:20:42 -0800 [thread overview]
Message-ID: <563B81DA.2080409@redhat.com> (raw)
In-Reply-To: <20151105094615.GP8644@n2100.arm.linux.org.uk>
On 11/05/2015 01:46 AM, Russell King - ARM Linux wrote:
> On Wed, Nov 04, 2015 at 05:00:39PM -0800, Laura Abbott wrote:
>> Currently, read only permissions are not being applied even
>> when CONFIG_DEBUG_RODATA is set. This is because section_update
>> uses current->mm for adjusting the page tables. current->mm
>> need not be equivalent to the kernel version. Use pgd_offset_k
>> to get the proper page directory for updating.
>
> What are you trying to achieve here? You can't use these functions
> at run time (after the first thread has been spawned) to change
> permissions, because there will be multiple copies of the kernel
> section mappings, and those copies will not get updated.
>
> In any case, this change will probably break kexec and ftrace, as
> the running thread will no longer see the updated page tables.
>
I think I was hitting that exact problem with multiple copies
not getting updated. The section_update code was being called
and I was seeing the tables get updated but nothing was being
applied when I tried to write to text or check the debugfs
page table. The current flow is:
rest_init -> kernel_thread(kernel_init) and from that thread
mark_rodata_ro. So mark_rodata_ro is always going to happen
in a thread.
Do we need to update for both init_mm and the first running
thread?
Thanks,
Laura
WARNING: multiple messages have this Message-ID (diff)
From: Laura Abbott <labbott@redhat.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>,
Laura Abbott <labbott@fedoraproject.org>
Cc: Kees Cook <keescook@chromium.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] arm: Use kernel mm when updating section permissions
Date: Thu, 5 Nov 2015 08:20:42 -0800 [thread overview]
Message-ID: <563B81DA.2080409@redhat.com> (raw)
In-Reply-To: <20151105094615.GP8644@n2100.arm.linux.org.uk>
On 11/05/2015 01:46 AM, Russell King - ARM Linux wrote:
> On Wed, Nov 04, 2015 at 05:00:39PM -0800, Laura Abbott wrote:
>> Currently, read only permissions are not being applied even
>> when CONFIG_DEBUG_RODATA is set. This is because section_update
>> uses current->mm for adjusting the page tables. current->mm
>> need not be equivalent to the kernel version. Use pgd_offset_k
>> to get the proper page directory for updating.
>
> What are you trying to achieve here? You can't use these functions
> at run time (after the first thread has been spawned) to change
> permissions, because there will be multiple copies of the kernel
> section mappings, and those copies will not get updated.
>
> In any case, this change will probably break kexec and ftrace, as
> the running thread will no longer see the updated page tables.
>
I think I was hitting that exact problem with multiple copies
not getting updated. The section_update code was being called
and I was seeing the tables get updated but nothing was being
applied when I tried to write to text or check the debugfs
page table. The current flow is:
rest_init -> kernel_thread(kernel_init) and from that thread
mark_rodata_ro. So mark_rodata_ro is always going to happen
in a thread.
Do we need to update for both init_mm and the first running
thread?
Thanks,
Laura
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WARNING: multiple messages have this Message-ID (diff)
From: labbott@redhat.com (Laura Abbott)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm: Use kernel mm when updating section permissions
Date: Thu, 5 Nov 2015 08:20:42 -0800 [thread overview]
Message-ID: <563B81DA.2080409@redhat.com> (raw)
In-Reply-To: <20151105094615.GP8644@n2100.arm.linux.org.uk>
On 11/05/2015 01:46 AM, Russell King - ARM Linux wrote:
> On Wed, Nov 04, 2015 at 05:00:39PM -0800, Laura Abbott wrote:
>> Currently, read only permissions are not being applied even
>> when CONFIG_DEBUG_RODATA is set. This is because section_update
>> uses current->mm for adjusting the page tables. current->mm
>> need not be equivalent to the kernel version. Use pgd_offset_k
>> to get the proper page directory for updating.
>
> What are you trying to achieve here? You can't use these functions
> at run time (after the first thread has been spawned) to change
> permissions, because there will be multiple copies of the kernel
> section mappings, and those copies will not get updated.
>
> In any case, this change will probably break kexec and ftrace, as
> the running thread will no longer see the updated page tables.
>
I think I was hitting that exact problem with multiple copies
not getting updated. The section_update code was being called
and I was seeing the tables get updated but nothing was being
applied when I tried to write to text or check the debugfs
page table. The current flow is:
rest_init -> kernel_thread(kernel_init) and from that thread
mark_rodata_ro. So mark_rodata_ro is always going to happen
in a thread.
Do we need to update for both init_mm and the first running
thread?
Thanks,
Laura
next prev parent reply other threads:[~2015-11-05 16:20 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-05 1:00 [PATCH] arm: Use kernel mm when updating section permissions Laura Abbott
2015-11-05 1:00 ` Laura Abbott
2015-11-05 1:00 ` Laura Abbott
2015-11-05 1:06 ` Kees Cook
2015-11-05 1:06 ` Kees Cook
2015-11-05 1:06 ` Kees Cook
2015-11-05 1:13 ` Kees Cook
2015-11-05 1:13 ` Kees Cook
2015-11-05 1:13 ` Kees Cook
2015-11-05 9:46 ` Russell King - ARM Linux
2015-11-05 9:46 ` Russell King - ARM Linux
2015-11-05 9:46 ` Russell King - ARM Linux
2015-11-05 16:20 ` Laura Abbott [this message]
2015-11-05 16:20 ` Laura Abbott
2015-11-05 16:20 ` Laura Abbott
2015-11-05 16:27 ` Russell King - ARM Linux
2015-11-05 16:27 ` Russell King - ARM Linux
2015-11-05 16:27 ` Russell King - ARM Linux
2015-11-06 1:05 ` Laura Abbott
2015-11-06 1:05 ` Laura Abbott
2015-11-06 1:05 ` Laura Abbott
2015-11-06 1:15 ` Kees Cook
2015-11-06 1:15 ` Kees Cook
2015-11-06 1:15 ` Kees Cook
2015-11-06 18:44 ` Laura Abbott
2015-11-06 18:44 ` Laura Abbott
2015-11-06 18:44 ` Laura Abbott
2015-11-06 19:08 ` Kees Cook
2015-11-06 19:08 ` Kees Cook
2015-11-06 19:08 ` Kees Cook
2015-11-06 19:12 ` Kees Cook
2015-11-06 19:12 ` Kees Cook
2015-11-06 19:12 ` Kees Cook
2015-11-06 20:11 ` Kevin Hilman
2015-11-06 20:11 ` Kevin Hilman
2015-11-06 20:11 ` Kevin Hilman
2015-11-06 20:28 ` Kees Cook
2015-11-06 20:28 ` Kees Cook
2015-11-06 20:28 ` Kees Cook
2015-11-06 21:06 ` Kevin Hilman
2015-11-06 21:06 ` Kevin Hilman
2015-11-06 21:06 ` Kevin Hilman
2015-11-06 21:19 ` Kees Cook
2015-11-06 21:19 ` Kees Cook
2015-11-06 21:19 ` Kees Cook
2015-11-06 22:37 ` Kevin Hilman
2015-11-06 22:37 ` Kevin Hilman
2015-11-06 22:37 ` Kevin Hilman
2015-11-06 23:05 ` Kevin Hilman
2015-11-06 23:05 ` Kevin Hilman
2015-11-06 23:05 ` Kevin Hilman
2015-11-06 23:47 ` Kees Cook
2015-11-06 23:47 ` Kees Cook
2015-11-06 23:47 ` Kees Cook
2015-11-06 20:46 ` Russell King - ARM Linux
2015-11-06 20:46 ` Russell King - ARM Linux
2015-11-06 20:46 ` Russell King - ARM Linux
2015-11-06 23:41 ` Laura Abbott
2015-11-06 23:41 ` Laura Abbott
2015-11-06 23:41 ` Laura Abbott
2015-11-06 23:49 ` Kees Cook
2015-11-06 23:49 ` Kees Cook
2015-11-06 23:49 ` Kees Cook
2015-11-07 0:20 ` Laura Abbott
2015-11-07 0:20 ` Laura Abbott
2015-11-07 0:20 ` Laura Abbott
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