[PATCH] arm64: vdso: Mark vDSO code as read-only

Subsystems: arm64 port (aarch64 architecture), the rest

STALE3819d

6 messages, 4 authors, 2016-02-16 · open the first message on its own page

[PATCH] arm64: vdso: Mark vDSO code as read-only

From: David Brown <hidden>
Date: 2016-02-10 21:52:57 

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 <redacted>
---
 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"
-- 
2.7.1

Re: [PATCH] arm64: vdso: Mark vDSO code as read-only

From: Will Deacon <hidden>
Date: 2016-02-11 13:47:03 

On Wed, Feb 10, 2016 at 01:52:22PM -0800, David Brown wrote:
quoted hunk
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 <redacted>
---
 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 <redacted>

As an aside, I wonder whether we should be printing the code/data
addresses out in dmesg at all.

Will

Re: [kernel-hardening] [PATCH] arm64: vdso: Mark vDSO code as read-only

From: Ard Biesheuvel <hidden>
Date: 2016-02-11 14:19:27 

Hi David,

Nice find!

On 10 February 2016 at 22:52, David Brown [off-list ref] wrote:
quoted hunk
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 <redacted>
---
 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
^^ You can get rid of this now as well

Acked-by: Ard Biesheuvel <redacted>

        .globl vdso_start, vdso_end
+       .section .rodata
        .balign PAGE_SIZE
 vdso_start:
        .incbin "arch/arm64/kernel/vdso/vdso.so"
--
2.7.1

Re: [kernel-hardening] [PATCH] arm64: vdso: Mark vDSO code as read-only

From: David Brown <hidden>
Date: 2016-02-13 00:31:52 

On Thu, Feb 11, 2016 at 03:19:20PM +0100, Ard Biesheuvel wrote:
quoted
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
^^ You can get rid of this now as well
Can we?  The page is getting mapped to userspace, and if we didn't
page align it, we could leak kernel read-only data to every userspace
process.

David

Re: [kernel-hardening] [PATCH] arm64: vdso: Mark vDSO code as read-only

From: Ard Biesheuvel <hidden>
Date: 2016-02-13 09:00:58 

On 13 February 2016 at 01:31, David Brown [off-list ref] wrote:
On Thu, Feb 11, 2016 at 03:19:20PM +0100, Ard Biesheuvel wrote:
quoted
quoted
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

^^ You can get rid of this now as well

Can we?  The page is getting mapped to userspace, and if we didn't
page align it, we could leak kernel read-only data to every userspace
process.
That's what the .balign is for. __PAGE_ALIGNED_DATA only sets the
section, and you're overriding that right after.

Re: [PATCH] arm64: vdso: Mark vDSO code as read-only

From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2016-02-16 18:22:40 

On Wed, Feb 10, 2016 at 01:52:22PM -0800, David Brown wrote:
quoted hunk
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"
-- 
2.7.1
Patch applied (and removed __PAGE_ALIGNED_DATA as well). Thanks.

-- 
Catalin
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help