* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-10 17:55 Kees Cook
2016-05-11 9:44 ` Jon Medhurst (Tixy)
0 siblings, 1 reply; 5+ messages in thread
From: Kees Cook @ 2016-05-10 17:55 UTC (permalink / raw)
To: linux-arm-kernel
This fixes two issues with the arm64 brk randomziation. First, the
STACK_RND_MASK was being used incorrectly. The original code was:
unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where
PAGE_SHIFT is 12:
#define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \
0x7ff >> (PAGE_SHIFT - 12) : \
0x3ffff >> (PAGE_SHIFT - 12))
This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001,
which is wrong since it creates an unaligned end address. It was likely
intended to be:
unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT)
Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit).
However, even this corrected 32-bit compat offset (0x00800000) is much
smaller than native ARM's brk randomization value (0x02000000):
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
unsigned long range_end = mm->brk + 0x02000000;
return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
}
So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK
calculations, just use specific corrected values for compat (0x2000000)
and native arm64 (0x40000000).
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm64/kernel/process.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 80624829db61..0d0969bcd76d 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -382,13 +382,14 @@ unsigned long arch_align_stack(unsigned long sp)
return sp & ~0xf;
}
-static unsigned long randomize_base(unsigned long base)
-{
- unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
- return randomize_range(base, range_end, 0) ? : base;
-}
-
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
- return randomize_base(mm->brk);
+ unsigned long range_end = mm->brk;
+
+ if (test_thread_flag(TIF_32BIT))
+ range_end += 0x02000000;
+ else
+ range_end += 0x40000000;
+
+ return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
}
--
2.6.3
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH] arm64: kernel: Fix incorrect brk randomization
2016-05-10 17:55 [PATCH] arm64: kernel: Fix incorrect brk randomization Kees Cook
@ 2016-05-11 9:44 ` Jon Medhurst (Tixy)
2016-05-11 15:27 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: Jon Medhurst (Tixy) @ 2016-05-11 9:44 UTC (permalink / raw)
To: linux-arm-kernel
On Tue, 2016-05-10 at 10:55 -0700, Kees Cook wrote:
> This fixes two issues with the arm64 brk randomziation. First, the
> STACK_RND_MASK was being used incorrectly. The original code was:
>
> unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
>
> STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where
> PAGE_SHIFT is 12:
>
> #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \
> 0x7ff >> (PAGE_SHIFT - 12) : \
> 0x3ffff >> (PAGE_SHIFT - 12))
>
> This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001,
> which is wrong since it creates an unaligned end address. It was likely
> intended to be:
>
> unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT)
>
> Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit).
>
> However, even this corrected 32-bit compat offset (0x00800000) is much
> smaller than native ARM's brk randomization value (0x02000000):
>
> unsigned long arch_randomize_brk(struct mm_struct *mm)
> {
> unsigned long range_end = mm->brk + 0x02000000;
> return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> }
>
> So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK
> calculations, just use specific corrected values for compat (0x2000000)
> and native arm64 (0x40000000).
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
There seems to be a helper 'is_compat_task()' that does
'test_thread_flag(TIF_32BIT)' so could perhaps be used instead, but
that's too nit-picky. This change makes things more consistent with
arch/arm and other arches, and stops use of STACK_RND_MASK for things
that aren't stack related so seems good all round to me.
Reviewed-by: Jon Medhurst <tixy@linaro.org>
> ---
> arch/arm64/kernel/process.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 80624829db61..0d0969bcd76d 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -382,13 +382,14 @@ unsigned long arch_align_stack(unsigned long sp)
> return sp & ~0xf;
> }
>
> -static unsigned long randomize_base(unsigned long base)
> -{
> - unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
> - return randomize_range(base, range_end, 0) ? : base;
> -}
> -
> unsigned long arch_randomize_brk(struct mm_struct *mm)
> {
> - return randomize_base(mm->brk);
> + unsigned long range_end = mm->brk;
> +
> + if (test_thread_flag(TIF_32BIT))
> + range_end += 0x02000000;
> + else
> + range_end += 0x40000000;
> +
> + return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> }
> --
> 2.6.3
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH] arm64: kernel: Fix incorrect brk randomization
2016-05-11 9:44 ` Jon Medhurst (Tixy)
@ 2016-05-11 15:27 ` Kees Cook
2016-05-11 15:29 ` Will Deacon
0 siblings, 1 reply; 5+ messages in thread
From: Kees Cook @ 2016-05-11 15:27 UTC (permalink / raw)
To: linux-arm-kernel
On Wed, May 11, 2016 at 2:44 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
> On Tue, 2016-05-10 at 10:55 -0700, Kees Cook wrote:
>> This fixes two issues with the arm64 brk randomziation. First, the
>> STACK_RND_MASK was being used incorrectly. The original code was:
>>
>> unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
>>
>> STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where
>> PAGE_SHIFT is 12:
>>
>> #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \
>> 0x7ff >> (PAGE_SHIFT - 12) : \
>> 0x3ffff >> (PAGE_SHIFT - 12))
>>
>> This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001,
>> which is wrong since it creates an unaligned end address. It was likely
>> intended to be:
>>
>> unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT)
>>
>> Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit).
>>
>> However, even this corrected 32-bit compat offset (0x00800000) is much
>> smaller than native ARM's brk randomization value (0x02000000):
>>
>> unsigned long arch_randomize_brk(struct mm_struct *mm)
>> {
>> unsigned long range_end = mm->brk + 0x02000000;
>> return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
>> }
>>
>> So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK
>> calculations, just use specific corrected values for compat (0x2000000)
>> and native arm64 (0x40000000).
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>
> There seems to be a helper 'is_compat_task()' that does
> 'test_thread_flag(TIF_32BIT)' so could perhaps be used instead, but
> that's too nit-picky. This change makes things more consistent with
Oh, good call. Yeah, none of the other .c code does direct tests for
the TIF_32BIT flag, so I'll use the helper and send a v2. Thanks!
-Kees
> arch/arm and other arches, and stops use of STACK_RND_MASK for things
> that aren't stack related so seems good all round to me.
>
> Reviewed-by: Jon Medhurst <tixy@linaro.org>
>
>> ---
>> arch/arm64/kernel/process.c | 15 ++++++++-------
>> 1 file changed, 8 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index 80624829db61..0d0969bcd76d 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -382,13 +382,14 @@ unsigned long arch_align_stack(unsigned long sp)
>> return sp & ~0xf;
>> }
>>
>> -static unsigned long randomize_base(unsigned long base)
>> -{
>> - unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
>> - return randomize_range(base, range_end, 0) ? : base;
>> -}
>> -
>> unsigned long arch_randomize_brk(struct mm_struct *mm)
>> {
>> - return randomize_base(mm->brk);
>> + unsigned long range_end = mm->brk;
>> +
>> + if (test_thread_flag(TIF_32BIT))
>> + range_end += 0x02000000;
>> + else
>> + range_end += 0x40000000;
>> +
>> + return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
>> }
>> --
>> 2.6.3
>>
>>
>
>
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH] arm64: kernel: Fix incorrect brk randomization
2016-05-11 15:27 ` Kees Cook
@ 2016-05-11 15:29 ` Will Deacon
2016-05-11 15:30 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: Will Deacon @ 2016-05-11 15:29 UTC (permalink / raw)
To: linux-arm-kernel
On Wed, May 11, 2016 at 08:27:14AM -0700, Kees Cook wrote:
> On Wed, May 11, 2016 at 2:44 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
> > On Tue, 2016-05-10 at 10:55 -0700, Kees Cook wrote:
> >> This fixes two issues with the arm64 brk randomziation. First, the
> >> STACK_RND_MASK was being used incorrectly. The original code was:
> >>
> >> unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
> >>
> >> STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where
> >> PAGE_SHIFT is 12:
> >>
> >> #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \
> >> 0x7ff >> (PAGE_SHIFT - 12) : \
> >> 0x3ffff >> (PAGE_SHIFT - 12))
> >>
> >> This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001,
> >> which is wrong since it creates an unaligned end address. It was likely
> >> intended to be:
> >>
> >> unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT)
> >>
> >> Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit).
> >>
> >> However, even this corrected 32-bit compat offset (0x00800000) is much
> >> smaller than native ARM's brk randomization value (0x02000000):
> >>
> >> unsigned long arch_randomize_brk(struct mm_struct *mm)
> >> {
> >> unsigned long range_end = mm->brk + 0x02000000;
> >> return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> >> }
> >>
> >> So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK
> >> calculations, just use specific corrected values for compat (0x2000000)
> >> and native arm64 (0x40000000).
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > There seems to be a helper 'is_compat_task()' that does
> > 'test_thread_flag(TIF_32BIT)' so could perhaps be used instead, but
> > that's too nit-picky. This change makes things more consistent with
>
> Oh, good call. Yeah, none of the other .c code does direct tests for
> the TIF_32BIT flag, so I'll use the helper and send a v2. Thanks!
I already applied it with that change and Tixy's reviewed-by. Thanks!
Will
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH] arm64: kernel: Fix incorrect brk randomization
2016-05-11 15:29 ` Will Deacon
@ 2016-05-11 15:30 ` Kees Cook
0 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2016-05-11 15:30 UTC (permalink / raw)
To: linux-arm-kernel
On Wed, May 11, 2016 at 8:29 AM, Will Deacon <will.deacon@arm.com> wrote:
> On Wed, May 11, 2016 at 08:27:14AM -0700, Kees Cook wrote:
>> On Wed, May 11, 2016 at 2:44 AM, Jon Medhurst (Tixy) <tixy@linaro.org> wrote:
>> > On Tue, 2016-05-10 at 10:55 -0700, Kees Cook wrote:
>> >> This fixes two issues with the arm64 brk randomziation. First, the
>> >> STACK_RND_MASK was being used incorrectly. The original code was:
>> >>
>> >> unsigned long range_end = base + (STACK_RND_MASK << PAGE_SHIFT) + 1;
>> >>
>> >> STACK_RND_MASK is 0x7ff (32-bit) or 0x3ffff (64-bit), with 4K pages where
>> >> PAGE_SHIFT is 12:
>> >>
>> >> #define STACK_RND_MASK (test_thread_flag(TIF_32BIT) ? \
>> >> 0x7ff >> (PAGE_SHIFT - 12) : \
>> >> 0x3ffff >> (PAGE_SHIFT - 12))
>> >>
>> >> This means the resulting offset from base would be 0x7ff0001 or 0x3ffff0001,
>> >> which is wrong since it creates an unaligned end address. It was likely
>> >> intended to be:
>> >>
>> >> unsigned long range_end = base + ((STACK_RND_MASK + 1) << PAGE_SHIFT)
>> >>
>> >> Which would result in offsets of 0x800000 (32-bit) and 0x40000000 (64-bit).
>> >>
>> >> However, even this corrected 32-bit compat offset (0x00800000) is much
>> >> smaller than native ARM's brk randomization value (0x02000000):
>> >>
>> >> unsigned long arch_randomize_brk(struct mm_struct *mm)
>> >> {
>> >> unsigned long range_end = mm->brk + 0x02000000;
>> >> return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
>> >> }
>> >>
>> >> So, instead of basing arm64's brk randomization on mistaken STACK_RND_MASK
>> >> calculations, just use specific corrected values for compat (0x2000000)
>> >> and native arm64 (0x40000000).
>> >>
>> >> Signed-off-by: Kees Cook <keescook@chromium.org>
>> >
>> > There seems to be a helper 'is_compat_task()' that does
>> > 'test_thread_flag(TIF_32BIT)' so could perhaps be used instead, but
>> > that's too nit-picky. This change makes things more consistent with
>>
>> Oh, good call. Yeah, none of the other .c code does direct tests for
>> the TIF_32BIT flag, so I'll use the helper and send a v2. Thanks!
>
> I already applied it with that change and Tixy's reviewed-by. Thanks!
Oh! Perfect, thanks! :)
-Kees
--
Kees Cook
Chrome OS & Brillo Security
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-05-10 17:55 [PATCH] arm64: kernel: Fix incorrect brk randomization Kees Cook
2016-05-11 9:44 ` Jon Medhurst (Tixy)
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2016-05-11 15:29 ` Will Deacon
2016-05-11 15:30 ` Kees Cook
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