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Message-ID: <20160211134702.GE32084@arm.com>
Date: Thu, 11 Feb 2016 13:47:03 +0000
From: Will Deacon <will.deacon@....com>
To: David Brown <david.brown@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] arm64: vdso: Mark vDSO code as read-only
On Wed, Feb 10, 2016 at 01:52:22PM -0800, David Brown wrote:
> Although the arm64 vDSO is cleanly separated by code/data with the
> code being read-only in userspace mappings, the code page is still
> writable from the kernel. There have been exploits (such as
> http://itszn.com/blog/?p=21) that take advantage of this on x86 to go
> from a bad kernel write to full root.
>
> Prevent this specific exploit on arm64 by putting the vDSO code page
> in read-only memory as well.
>
> Before the change:
> [ 3.138366] vdso: 2 pages (1 code @ ffffffc000a71000, 1 data @ ffffffc000a70000)
> ---[ Kernel Mapping ]---
> 0xffffffc000000000-0xffffffc000082000 520K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc000082000-0xffffffc000200000 1528K ro x SHD AF UXN MEM/NORMAL
> 0xffffffc000200000-0xffffffc000800000 6M ro x SHD AF BLK UXN MEM/NORMAL
> 0xffffffc000800000-0xffffffc0009b6000 1752K ro x SHD AF UXN MEM/NORMAL
> 0xffffffc0009b6000-0xffffffc000c00000 2344K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc000c00000-0xffffffc008000000 116M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc00c000000-0xffffffc07f000000 1840M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc800000000-0xffffffc840000000 1G RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc840000000-0xffffffc87ae00000 942M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc87ae00000-0xffffffc87ae70000 448K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87af80000-0xffffffc87af8a000 40K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87af8b000-0xffffffc87b000000 468K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87b000000-0xffffffc87fe00000 78M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc87fe00000-0xffffffc87ff50000 1344K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87ff90000-0xffffffc87ffa0000 64K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87fff0000-0xffffffc880000000 64K RW NX SHD AF UXN MEM/NORMAL
>
> After:
> [ 3.138368] vdso: 2 pages (1 code @ ffffffc0006de000, 1 data @ ffffffc000a74000)
> ---[ Kernel Mapping ]---
> 0xffffffc000000000-0xffffffc000082000 520K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc000082000-0xffffffc000200000 1528K ro x SHD AF UXN MEM/NORMAL
> 0xffffffc000200000-0xffffffc000800000 6M ro x SHD AF BLK UXN MEM/NORMAL
> 0xffffffc000800000-0xffffffc0009b8000 1760K ro x SHD AF UXN MEM/NORMAL
> 0xffffffc0009b8000-0xffffffc000c00000 2336K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc000c00000-0xffffffc008000000 116M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc00c000000-0xffffffc07f000000 1840M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc800000000-0xffffffc840000000 1G RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc840000000-0xffffffc87ae00000 942M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc87ae00000-0xffffffc87ae70000 448K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87af80000-0xffffffc87af8a000 40K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87af8b000-0xffffffc87b000000 468K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87b000000-0xffffffc87fe00000 78M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffffc87fe00000-0xffffffc87ff50000 1344K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87ff90000-0xffffffc87ffa0000 64K RW NX SHD AF UXN MEM/NORMAL
> 0xffffffc87fff0000-0xffffffc880000000 64K RW NX SHD AF UXN MEM/NORMAL
>
> Inspired by https://lkml.org/lkml/2016/1/19/494 based on work by the
> PaX Team, Brad Spengler, and Kees Cook.
>
> Signed-off-by: David Brown <david.brown@...aro.org>
> ---
> arch/arm64/kernel/vdso/vdso.S | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/kernel/vdso/vdso.S b/arch/arm64/kernel/vdso/vdso.S
> index 60c1db5..db7c0f2 100644
> --- a/arch/arm64/kernel/vdso/vdso.S
> +++ b/arch/arm64/kernel/vdso/vdso.S
> @@ -24,6 +24,7 @@
> __PAGE_ALIGNED_DATA
>
> .globl vdso_start, vdso_end
> + .section .rodata
> .balign PAGE_SIZE
> vdso_start:
> .incbin "arch/arm64/kernel/vdso/vdso.so"
Nice, I wish I'd thought of that!
Acked-by: Will Deacon <will.deacon@....com>
As an aside, I wonder whether we should be printing the code/data
addresses out in dmesg at all.
Will
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