Re: [PATCH] arm64: dump: hide kernel pointers
From: Laura Abbott
Date: Wed Mar 01 2017 - 01:08:39 EST
On 02/28/2017 02:04 AM, Mark Rutland wrote:
> On Tue, Feb 28, 2017 at 08:42:51AM +0000, Ard Biesheuvel wrote:
>> (+ Mark)
>
> (+ Laura)
>
>> On 28 February 2017 at 07:05, Miles Chen <miles.chen@xxxxxxxxxxxx> wrote:
>>> Mask kernel pointers of /sys/kernel/debug/kernel_page_tables entry like
>>> /proc/vmallocinfo does.
>>>
>>> With sysctl kernel.kptr_restrict=0 or 1:
>>> cat /sys/kernel/debug/kernel_page_tables
>>
>> I wonder if this file should be accessible at all if kptr_restrict > 0
>
> I don't have strong feelings either way.
>
> This isn't typically enabled, and it's under debugfs, so this shouldn't
> be accessible by a typical user anyhow.
>
> That said, there are very few of us who need to take a look at this
> file. I'm happy to deal with attacking kptr_restrict when required.
>
In the interest of security it's probably for the best to switch to the
restricted pointer. Who knows what might get enabled or forgotten about.
I don't like the idea of tying enablement of the file to kptr_restrict
though.
This should probably be fixed up on all arches that implement the
page table dump feature.
Laura
> Thanks,
> Mark.
>
>>> ---[ Modules start ]---
>>> ---[ Modules end ]---
>>> ---[ vmalloc() Area ]---
>>> ffffff8008000000-ffffff8008010000 64K PTE RW NX SHD AF...
>>> ffffff8008015000-ffffff8008016000 4K PTE RW NX SHD AF...
>>> ffffff8008020000-ffffff8008030000 64K PTE RW NX SHD AF...
>>> ffffff8008031000-ffffff8008071000 256K PTE RW NX SHD AF...
>>> ffffff8008080000-ffffff8008200000 1536K PTE ro x SHD AF...
>>> ffffff8008200000-ffffff8008400000 2M PMD ro x SHD AF...
>>> ffffff8008400000-ffffff8008540000 1280K PTE ro x SHD AF...
>>> ffffff8008540000-ffffff8008690000 1344K PTE ro NX SHD AF...
>>> ffffff8008940000-ffffff8008a10000 832K PTE RW NX SHD AF...
>>> ffffff8008aca000-ffffff8008acd000 12K PTE RW NX SHD AF...
>>> ffffffbebffd8000-ffffffbebffdb000 12K PTE RW NX SHD AF...
>>> ---[ vmalloc() End ]---
>>> ---[ Fixmap start ]---
>>> ffffffbefe800000-ffffffbefea00000 2M PMD ro NX SHD AF...
>>> ---[ Fixmap end ]---
>>> ---[ PCI I/O start ]---
>>> ---[ PCI I/O end ]---
>>> ---[ Linear Mapping ]---
>>> ffffffc000000000-ffffffc000080000 512K PTE RW NX SHD AF...
>>> ffffffc000080000-ffffffc000200000 1536K PTE ro NX SHD AF...
>>> ffffffc000200000-ffffffc000600000 4M PMD ro NX SHD AF...
>>> ffffffc000600000-ffffffc000690000 576K PTE ro NX SHD AF...
>>> ffffffc000690000-ffffffc000800000 1472K PTE RW NX SHD AF...
>>> ffffffc000800000-ffffffc002000000 24M PMD RW NX SHD AF...
>>> ffffffc002000000-ffffffc040000000 992M PMD RW NX SHD AF...
>>> ffffffc040000000-ffffffc080000000 1G PGD RW NX SHD AF...
>>>
>>> With sysctl kernel.kptr_restrict=2:
>>> cat /sys/kernel/debug/kernel_page_tables
>>> ---[ Modules start ]---
>>> ---[ Modules end ]---
>>> ---[ vmalloc() Area ]---
>>> 0000000000000000-0000000000000000 64K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 4K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 64K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 256K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 1536K PTE ro x SHD AF...
>>> 0000000000000000-0000000000000000 2M PMD ro x SHD AF...
>>> 0000000000000000-0000000000000000 1280K PTE ro x SHD AF...
>>> 0000000000000000-0000000000000000 1344K PTE ro NX SHD AF...
>>> 0000000000000000-0000000000000000 832K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 12K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 12K PTE RW NX SHD AF...
>>> ---[ vmalloc() End ]---
>>> ---[ Fixmap start ]---
>>> 0000000000000000-0000000000000000 2M PMD ro NX SHD AF...
>>> ---[ Fixmap end ]---
>>> ---[ PCI I/O start ]---
>>> ---[ PCI I/O end ]---
>>> ---[ Linear Mapping ]---
>>> 0000000000000000-0000000000000000 512K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 1536K PTE ro NX SHD AF...
>>> 0000000000000000-0000000000000000 4M PMD ro NX SHD AF...
>>> 0000000000000000-0000000000000000 576K PTE ro NX SHD AF...
>>> 0000000000000000-0000000000000000 1472K PTE RW NX SHD AF...
>>> 0000000000000000-0000000000000000 24M PMD RW NX SHD AF...
>>> 0000000000000000-0000000000000000 992M PMD RW NX SHD AF...
>>> 0000000000000000-0000000000000000 1G PGD RW NX SHD AF...
>>>
>>> Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
>>> ---
>>> arch/arm64/mm/dump.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
>>> index ca74a2a..e055ecf 100644
>>> --- a/arch/arm64/mm/dump.c
>>> +++ b/arch/arm64/mm/dump.c
>>> @@ -253,8 +253,8 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level,
>>> if (st->current_prot) {
>>> note_prot_uxn(st, addr);
>>> note_prot_wx(st, addr);
>>> - pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx ",
>>> - st->start_address, addr);
>>> + pt_dump_seq_printf(st->seq, "%pK-%pK ",
>>> + (void *)st->start_address, (void *)addr);
>>>
>>> delta = (addr - st->start_address) >> 10;
>>> while (!(delta & 1023) && unit[1]) {
>>> --
>>> 1.9.1
>>>
>>>
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