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* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-10 17:55 ` Kees Cook
  0 siblings, 0 replies; 10+ messages in thread
From: Kees Cook @ 2016-05-10 17:55 UTC (permalink / raw)
  To: Catalin Marinas
  Cc: Jon Medhurst (Tixy),
	Hector Marco, Nicolas Pitre, Will Deacon, AKASHI Takahiro,
	Lorenzo Pieralisi, Jisheng Zhang, Mark Rutland, James Morse,
	linux-arm-kernel, linux-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] 10+ messages in thread
* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-10 17:55 ` Kees Cook
  0 siblings, 0 replies; 10+ 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] 10+ messages in thread
* Re: [PATCH] arm64: kernel: Fix incorrect brk randomization
  2016-05-10 17:55 ` Kees Cook
@ 2016-05-11  9:44   ` Jon Medhurst (Tixy)
  -1 siblings, 0 replies; 10+ messages in thread
From: Jon Medhurst (Tixy) @ 2016-05-11  9:44 UTC (permalink / raw)
  To: Kees Cook
  Cc: Catalin Marinas, Hector Marco, Nicolas Pitre, Will Deacon,
	AKASHI Takahiro, Lorenzo Pieralisi, Jisheng Zhang, Mark Rutland,
	James Morse, linux-arm-kernel, linux-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] 10+ messages in thread
* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-11  9:44   ` Jon Medhurst (Tixy)
  0 siblings, 0 replies; 10+ 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] 10+ messages in thread
* Re: [PATCH] arm64: kernel: Fix incorrect brk randomization
  2016-05-11  9:44   ` Jon Medhurst (Tixy)
@ 2016-05-11 15:27     ` Kees Cook
  -1 siblings, 0 replies; 10+ messages in thread
From: Kees Cook @ 2016-05-11 15:27 UTC (permalink / raw)
  To: Jon Medhurst (Tixy)
  Cc: Catalin Marinas, Hector Marco, Nicolas Pitre, Will Deacon,
	AKASHI Takahiro, Lorenzo Pieralisi, Jisheng Zhang, Mark Rutland,
	James Morse, linux-arm-kernel, LKML

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] 10+ messages in thread
* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-11 15:27     ` Kees Cook
  0 siblings, 0 replies; 10+ 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] 10+ messages in thread
* Re: [PATCH] arm64: kernel: Fix incorrect brk randomization
  2016-05-11 15:27     ` Kees Cook
@ 2016-05-11 15:29       ` Will Deacon
  -1 siblings, 0 replies; 10+ messages in thread
From: Will Deacon @ 2016-05-11 15:29 UTC (permalink / raw)
  To: Kees Cook
  Cc: Jon Medhurst (Tixy),
	Catalin Marinas, Hector Marco, Nicolas Pitre, AKASHI Takahiro,
	Lorenzo Pieralisi, Jisheng Zhang, Mark Rutland, James Morse,
	linux-arm-kernel, LKML

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] 10+ messages in thread
* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-11 15:29       ` Will Deacon
  0 siblings, 0 replies; 10+ 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] 10+ messages in thread
* Re: [PATCH] arm64: kernel: Fix incorrect brk randomization
  2016-05-11 15:29       ` Will Deacon
@ 2016-05-11 15:30         ` Kees Cook
  -1 siblings, 0 replies; 10+ messages in thread
From: Kees Cook @ 2016-05-11 15:30 UTC (permalink / raw)
  To: Will Deacon
  Cc: Jon Medhurst (Tixy),
	Catalin Marinas, Hector Marco, Nicolas Pitre, AKASHI Takahiro,
	Lorenzo Pieralisi, Jisheng Zhang, Mark Rutland, James Morse,
	linux-arm-kernel, LKML

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] 10+ messages in thread
* [PATCH] arm64: kernel: Fix incorrect brk randomization
@ 2016-05-11 15:30         ` Kees Cook
  0 siblings, 0 replies; 10+ 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] 10+ messages in thread
end of thread, other threads:[~2016-05-11 15:30 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-05-10 17:55 [PATCH] arm64: kernel: Fix incorrect brk randomization Kees Cook
2016-05-10 17:55 ` Kees Cook
2016-05-11  9:44 ` Jon Medhurst (Tixy)
2016-05-11  9:44   ` Jon Medhurst (Tixy)
2016-05-11 15:27   ` Kees Cook
2016-05-11 15:27     ` Kees Cook
2016-05-11 15:29     ` Will Deacon
2016-05-11 15:29       ` Will Deacon
2016-05-11 15:30       ` Kees Cook
2016-05-11 15:30         ` Kees Cook

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