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* [PATCH 0/4] arm64/mm: migrate swapper_pg_dir
@ 2018-05-30  9:12 YaoJun
  2018-05-30  9:12 ` [PATCH 1/4] " YaoJun
                   ` (3 more replies)
  0 siblings, 4 replies; 9+ messages in thread
From: YaoJun @ 2018-05-30  9:12 UTC (permalink / raw)
  To: kernel-hardening
  Cc: catalin.marinas, will.deacon, linux-arm-kernel, linux-kernel,
	mark.rutland

Currently, The offset between swapper_pg_dir and _text is
fixed. When attackers know the address of _text(no KASLR or
breaking KASLR), they can caculate the address of
swapper_pg_dir. Then KSMA(Kernel Space Mirroring Attack) can
be applied.

The principle of KSMA is to insert a carefully constructed PGD
entry into the translation table. The type of this entry is
block, which maps the kernel text and its access permissions
bits are 01. The user process can then modify kernel text
directly through this mapping.

To protect against KSMA, these patches migrate swapper_pg_dir
to new place, which is dynamically allocated. Since it is
allocated during the kernel boot process and the address is
relatively fixed, further randomization may be required.

YaoJun (4):
  arm64/mm: Introduce __pa_swapper_pg_dir to save physical
	    address of swapper_pg_dir. And pass it as an
	    argument to __enable_mmu().
  arm64/mm: Introduce new_swapper_pg_dir to save virtual
	    address of new swapper_pg_dir.
  arm64/mm: Make tramp_pg_dir and swapper_pg_dir adjacent.
  arm64/mm: Migrate swapper_pg_dir and tramp_pg_dir.

 arch/arm64/include/asm/mmu_context.h |  6 +--
 arch/arm64/include/asm/pgtable.h     |  2 +
 arch/arm64/kernel/cpufeature.c       |  2 +-
 arch/arm64/kernel/entry.S            |  4 +-
 arch/arm64/kernel/head.S             | 10 ++--
 arch/arm64/kernel/hibernate.c        |  2 +-
 arch/arm64/kernel/sleep.S            |  2 +
 arch/arm64/kernel/vmlinux.lds.S      | 10 ++--
 arch/arm64/mm/kasan_init.c           |  6 +--
 arch/arm64/mm/mmu.c                  | 72 ++++++++++++++++++++--------
 10 files changed, 75 insertions(+), 41 deletions(-)

-- 
2.17.0

^ permalink raw reply	[flat|nested] 9+ messages in thread
* [PATCH 0/4] arm64/mm: migrate swapper_pg_dir
@ 2018-06-01  8:08 Jun Yao
  2018-06-01  9:42 ` Robin Murphy
  0 siblings, 1 reply; 9+ messages in thread
From: Jun Yao @ 2018-06-01  8:08 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: catalin.marinas, will.deacon, linux-kernel, kernel-hardening, greg

Currently, The offset between swapper_pg_dir and _text is
fixed. When attackers know the address of _text(no KASLR or
breaking KASLR), they can caculate the address of
swapper_pg_dir. Then KSMA(Kernel Space Mirroring Attack) can
be applied.

The principle of KSMA is to insert a carefully constructed PGD
entry into the translation table. The type of this entry is
block, which maps the kernel text and its access permissions
bits are 01. The user process can then modify kernel text
directly through this mapping.

To protect against KSMA, these patches migrate swapper_pg_dir
to new place, which is dynamically allocated. Since it is
allocated during the kernel boot process and the address is
relatively fixed, further randomization may be required.

Jun Yao (4):
  arm64/mm: pass swapper_pg_dir as an argument to __enable_mmu()
  arm64/mm: introduce variable to save new swapper_pg_dir address
  arm64/mm: make tramp_pg_dir and swapper_pg_dir adjacent
  arm64/mm: migrate swapper_pg_dir and tramp_pg_dir

 arch/arm64/include/asm/mmu_context.h |  6 +--
 arch/arm64/include/asm/pgtable.h     |  2 +
 arch/arm64/kernel/cpufeature.c       |  2 +-
 arch/arm64/kernel/entry.S            |  4 +-
 arch/arm64/kernel/head.S             | 10 ++--
 arch/arm64/kernel/hibernate.c        |  2 +-
 arch/arm64/kernel/sleep.S            |  2 +
 arch/arm64/kernel/vmlinux.lds.S      |  9 ++--
 arch/arm64/mm/kasan_init.c           |  6 +--
 arch/arm64/mm/mmu.c                  | 75 +++++++++++++++++-----------
 10 files changed, 71 insertions(+), 47 deletions(-)

-- 
2.17.0

^ permalink raw reply	[flat|nested] 9+ messages in thread
* Re: [PATCH 0/4] arm64/mm: migrate swapper_pg_dir
@ 2018-06-04  9:13 Jun Yao
  0 siblings, 0 replies; 9+ messages in thread
From: Jun Yao @ 2018-06-04  9:13 UTC (permalink / raw)
  To: robin.murphy, linux-arm-kernel
  Cc: catalin.marinas, will.deacon, linux-kernel, greg, kernel-hardening

On 1 Jun 2018 at 10:42:10, Robin Murphy <robin.murphy@arm.com> wrote:
>> Currently, The offset between swapper_pg_dir and _text is
>> fixed. When attackers know the address of _text(no KASLR or
>> breaking KASLR), they can caculate the address of
>> swapper_pg_dir. Then KSMA(Kernel Space Mirroring Attack) can
>> be applied.
>>
>> The principle of KSMA is to insert a carefully constructed PGD
>> entry into the translation table. The type of this entry is
>
>Out of interest, how does that part work? AFAICS, modifying a PGD entry
>involves writing to kernel memory, which would mean the implication of KSMA is
>"userspace can gain write permission to kernel memory by writing to kernel
>memory" - that doesn't sound like an attack in itself, more just a convenience
>for ease of exploiting whatever successful attack got you in there in the
>first place.
>
>That's not to say that it isn't still worth mitigating, I'm just questioning
>the given rationale here.

Yes, you are right. KSMA is just a convenience for ease of exploiting. I think
that the biggest role of KSMA is to covert an arbitrary write to multiple
arbitrary writes. In the past, to accomplish this, a function
pointer(e.g. ptmx_fops) is modified to point to gadget, which can r/w kernel
memory. However, PAN makes this more difficult. And KSMA becomes a new way to
do that.

For details on KSMA, you can refer to:

https://www.blackhat.com/docs/asia-18/asia-18-WANG-KSMA-Breaking-Android-kernel-isolation-and-Rooting-with-ARM-MMU-features.pdf

thanks,

Jun

^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2018-06-04  9:13 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-05-30  9:12 [PATCH 0/4] arm64/mm: migrate swapper_pg_dir YaoJun
2018-05-30  9:12 ` [PATCH 1/4] " YaoJun
2018-05-30  9:46   ` Greg KH
2018-05-30  9:12 ` [PATCH 2/4] " YaoJun
2018-05-30  9:12 ` [PATCH 3/4] " YaoJun
2018-05-30  9:12 ` [PATCH 4/4] " YaoJun
2018-06-01  8:08 [PATCH 0/4] " Jun Yao
2018-06-01  9:42 ` Robin Murphy
2018-06-04  9:13 Jun Yao

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