diff mbox series

[v4,08/14] arm: Use generic mmap top-down layout and brk randomization

Message ID 20190526134746.9315-9-alex@ghiti.fr (mailing list archive)
State Superseded
Headers show
Series Provide generic top-down mmap layout functions | expand

Commit Message

Alexandre Ghiti May 26, 2019, 1:47 p.m. UTC
arm uses a top-down mmap layout by default that exactly fits the generic
functions, so get rid of arch specific code and use the generic version
by selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
As ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects ARCH_HAS_ELF_RANDOMIZE,
use the generic version of arch_randomize_brk since it also fits.
Note that this commit also removes the possibility for arm to have elf
randomization and no MMU: without MMU, the security added by randomization
is worth nothing.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
 arch/arm/Kconfig                 |  2 +-
 arch/arm/include/asm/processor.h |  2 --
 arch/arm/kernel/process.c        |  5 ---
 arch/arm/mm/mmap.c               | 62 --------------------------------
 4 files changed, 1 insertion(+), 70 deletions(-)

Comments

Kees Cook May 29, 2019, 7:26 p.m. UTC | #1
On Sun, May 26, 2019 at 09:47:40AM -0400, Alexandre Ghiti wrote:
> arm uses a top-down mmap layout by default that exactly fits the generic
> functions, so get rid of arch specific code and use the generic version
> by selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
> As ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects ARCH_HAS_ELF_RANDOMIZE,
> use the generic version of arch_randomize_brk since it also fits.
> Note that this commit also removes the possibility for arm to have elf
> randomization and no MMU: without MMU, the security added by randomization
> is worth nothing.
> 
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>

Acked-by: Kees Cook <keescook@chromium.org>

It may be worth noting that STACK_RND_MASK is safe to remove here
because it matches the default that now exists in mm/util.c.

-Kees

> ---
>  arch/arm/Kconfig                 |  2 +-
>  arch/arm/include/asm/processor.h |  2 --
>  arch/arm/kernel/process.c        |  5 ---
>  arch/arm/mm/mmap.c               | 62 --------------------------------
>  4 files changed, 1 insertion(+), 70 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 8869742a85df..27687a8c9fb5 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -6,7 +6,6 @@ config ARM
>  	select ARCH_CLOCKSOURCE_DATA
>  	select ARCH_HAS_DEBUG_VIRTUAL if MMU
>  	select ARCH_HAS_DEVMEM_IS_ALLOWED
> -	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_FORTIFY_SOURCE
>  	select ARCH_HAS_KEEPINITRD
>  	select ARCH_HAS_KCOV
> @@ -29,6 +28,7 @@ config ARM
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF
> +	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>  	select ARCH_WANT_IPC_PARSE_VERSION
>  	select BUILDTIME_EXTABLE_SORT if MMU
>  	select CLONE_BACKWARDS
> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
> index 5d06f75ffad4..95b7688341c5 100644
> --- a/arch/arm/include/asm/processor.h
> +++ b/arch/arm/include/asm/processor.h
> @@ -143,8 +143,6 @@ static inline void prefetchw(const void *ptr)
>  #endif
>  #endif
>  
> -#define HAVE_ARCH_PICK_MMAP_LAYOUT
> -
>  #endif
>  
>  #endif /* __ASM_ARM_PROCESSOR_H */
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 72cc0862a30e..19a765db5f7f 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -322,11 +322,6 @@ unsigned long get_wchan(struct task_struct *p)
>  	return 0;
>  }
>  
> -unsigned long arch_randomize_brk(struct mm_struct *mm)
> -{
> -	return randomize_page(mm->brk, 0x02000000);
> -}
> -
>  #ifdef CONFIG_MMU
>  #ifdef CONFIG_KUSER_HELPERS
>  /*
> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> index 0b94b674aa91..b8d912ac9e61 100644
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
> @@ -17,43 +17,6 @@
>  	((((addr)+SHMLBA-1)&~(SHMLBA-1)) +	\
>  	 (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
>  
> -/* gap between mmap and stack */
> -#define MIN_GAP		(128*1024*1024UL)
> -#define MAX_GAP		((STACK_TOP)/6*5)
> -#define STACK_RND_MASK	(0x7ff >> (PAGE_SHIFT - 12))
> -
> -static int mmap_is_legacy(struct rlimit *rlim_stack)
> -{
> -	if (current->personality & ADDR_COMPAT_LAYOUT)
> -		return 1;
> -
> -	if (rlim_stack->rlim_cur == RLIM_INFINITY)
> -		return 1;
> -
> -	return sysctl_legacy_va_layout;
> -}
> -
> -static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> -{
> -	unsigned long gap = rlim_stack->rlim_cur;
> -	unsigned long pad = stack_guard_gap;
> -
> -	/* Account for stack randomization if necessary */
> -	if (current->flags & PF_RANDOMIZE)
> -		pad += (STACK_RND_MASK << PAGE_SHIFT);
> -
> -	/* Values close to RLIM_INFINITY can overflow. */
> -	if (gap + pad > gap)
> -		gap += pad;
> -
> -	if (gap < MIN_GAP)
> -		gap = MIN_GAP;
> -	else if (gap > MAX_GAP)
> -		gap = MAX_GAP;
> -
> -	return PAGE_ALIGN(STACK_TOP - gap - rnd);
> -}
> -
>  /*
>   * We need to ensure that shared mappings are correctly aligned to
>   * avoid aliasing issues with VIPT caches.  We need to ensure that
> @@ -181,31 +144,6 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
>  	return addr;
>  }
>  
> -unsigned long arch_mmap_rnd(void)
> -{
> -	unsigned long rnd;
> -
> -	rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> -
> -	return rnd << PAGE_SHIFT;
> -}
> -
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> -{
> -	unsigned long random_factor = 0UL;
> -
> -	if (current->flags & PF_RANDOMIZE)
> -		random_factor = arch_mmap_rnd();
> -
> -	if (mmap_is_legacy(rlim_stack)) {
> -		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
> -		mm->get_unmapped_area = arch_get_unmapped_area;
> -	} else {
> -		mm->mmap_base = mmap_base(random_factor, rlim_stack);
> -		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> -	}
> -}
> -
>  /*
>   * You really shouldn't be using read() or write() on /dev/mem.  This
>   * might go away in the future.
> -- 
> 2.20.1
>
Alexandre Ghiti May 31, 2019, 4:49 a.m. UTC | #2
On 5/29/19 3:26 PM, Kees Cook wrote:
> On Sun, May 26, 2019 at 09:47:40AM -0400, Alexandre Ghiti wrote:
>> arm uses a top-down mmap layout by default that exactly fits the generic
>> functions, so get rid of arch specific code and use the generic version
>> by selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.
>> As ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects ARCH_HAS_ELF_RANDOMIZE,
>> use the generic version of arch_randomize_brk since it also fits.
>> Note that this commit also removes the possibility for arm to have elf
>> randomization and no MMU: without MMU, the security added by randomization
>> is worth nothing.
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Acked-by: Kees Cook <keescook@chromium.org>
>
> It may be worth noting that STACK_RND_MASK is safe to remove here
> because it matches the default that now exists in mm/util.c.


Yes, thanks for pointing that.


Thanks,


Alex


>
> -Kees
>
>> ---
>>   arch/arm/Kconfig                 |  2 +-
>>   arch/arm/include/asm/processor.h |  2 --
>>   arch/arm/kernel/process.c        |  5 ---
>>   arch/arm/mm/mmap.c               | 62 --------------------------------
>>   4 files changed, 1 insertion(+), 70 deletions(-)
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index 8869742a85df..27687a8c9fb5 100644
>> --- a/arch/arm/Kconfig
>> +++ b/arch/arm/Kconfig
>> @@ -6,7 +6,6 @@ config ARM
>>   	select ARCH_CLOCKSOURCE_DATA
>>   	select ARCH_HAS_DEBUG_VIRTUAL if MMU
>>   	select ARCH_HAS_DEVMEM_IS_ALLOWED
>> -	select ARCH_HAS_ELF_RANDOMIZE
>>   	select ARCH_HAS_FORTIFY_SOURCE
>>   	select ARCH_HAS_KEEPINITRD
>>   	select ARCH_HAS_KCOV
>> @@ -29,6 +28,7 @@ config ARM
>>   	select ARCH_SUPPORTS_ATOMIC_RMW
>>   	select ARCH_USE_BUILTIN_BSWAP
>>   	select ARCH_USE_CMPXCHG_LOCKREF
>> +	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>>   	select ARCH_WANT_IPC_PARSE_VERSION
>>   	select BUILDTIME_EXTABLE_SORT if MMU
>>   	select CLONE_BACKWARDS
>> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
>> index 5d06f75ffad4..95b7688341c5 100644
>> --- a/arch/arm/include/asm/processor.h
>> +++ b/arch/arm/include/asm/processor.h
>> @@ -143,8 +143,6 @@ static inline void prefetchw(const void *ptr)
>>   #endif
>>   #endif
>>   
>> -#define HAVE_ARCH_PICK_MMAP_LAYOUT
>> -
>>   #endif
>>   
>>   #endif /* __ASM_ARM_PROCESSOR_H */
>> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
>> index 72cc0862a30e..19a765db5f7f 100644
>> --- a/arch/arm/kernel/process.c
>> +++ b/arch/arm/kernel/process.c
>> @@ -322,11 +322,6 @@ unsigned long get_wchan(struct task_struct *p)
>>   	return 0;
>>   }
>>   
>> -unsigned long arch_randomize_brk(struct mm_struct *mm)
>> -{
>> -	return randomize_page(mm->brk, 0x02000000);
>> -}
>> -
>>   #ifdef CONFIG_MMU
>>   #ifdef CONFIG_KUSER_HELPERS
>>   /*
>> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
>> index 0b94b674aa91..b8d912ac9e61 100644
>> --- a/arch/arm/mm/mmap.c
>> +++ b/arch/arm/mm/mmap.c
>> @@ -17,43 +17,6 @@
>>   	((((addr)+SHMLBA-1)&~(SHMLBA-1)) +	\
>>   	 (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
>>   
>> -/* gap between mmap and stack */
>> -#define MIN_GAP		(128*1024*1024UL)
>> -#define MAX_GAP		((STACK_TOP)/6*5)
>> -#define STACK_RND_MASK	(0x7ff >> (PAGE_SHIFT - 12))
>> -
>> -static int mmap_is_legacy(struct rlimit *rlim_stack)
>> -{
>> -	if (current->personality & ADDR_COMPAT_LAYOUT)
>> -		return 1;
>> -
>> -	if (rlim_stack->rlim_cur == RLIM_INFINITY)
>> -		return 1;
>> -
>> -	return sysctl_legacy_va_layout;
>> -}
>> -
>> -static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>> -{
>> -	unsigned long gap = rlim_stack->rlim_cur;
>> -	unsigned long pad = stack_guard_gap;
>> -
>> -	/* Account for stack randomization if necessary */
>> -	if (current->flags & PF_RANDOMIZE)
>> -		pad += (STACK_RND_MASK << PAGE_SHIFT);
>> -
>> -	/* Values close to RLIM_INFINITY can overflow. */
>> -	if (gap + pad > gap)
>> -		gap += pad;
>> -
>> -	if (gap < MIN_GAP)
>> -		gap = MIN_GAP;
>> -	else if (gap > MAX_GAP)
>> -		gap = MAX_GAP;
>> -
>> -	return PAGE_ALIGN(STACK_TOP - gap - rnd);
>> -}
>> -
>>   /*
>>    * We need to ensure that shared mappings are correctly aligned to
>>    * avoid aliasing issues with VIPT caches.  We need to ensure that
>> @@ -181,31 +144,6 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
>>   	return addr;
>>   }
>>   
>> -unsigned long arch_mmap_rnd(void)
>> -{
>> -	unsigned long rnd;
>> -
>> -	rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
>> -
>> -	return rnd << PAGE_SHIFT;
>> -}
>> -
>> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>> -{
>> -	unsigned long random_factor = 0UL;
>> -
>> -	if (current->flags & PF_RANDOMIZE)
>> -		random_factor = arch_mmap_rnd();
>> -
>> -	if (mmap_is_legacy(rlim_stack)) {
>> -		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
>> -		mm->get_unmapped_area = arch_get_unmapped_area;
>> -	} else {
>> -		mm->mmap_base = mmap_base(random_factor, rlim_stack);
>> -		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
>> -	}
>> -}
>> -
>>   /*
>>    * You really shouldn't be using read() or write() on /dev/mem.  This
>>    * might go away in the future.
>> -- 
>> 2.20.1
>>
diff mbox series

Patch

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8869742a85df..27687a8c9fb5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -6,7 +6,6 @@  config ARM
 	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
-	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_KEEPINITRD
 	select ARCH_HAS_KCOV
@@ -29,6 +28,7 @@  config ARM
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
+	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select BUILDTIME_EXTABLE_SORT if MMU
 	select CLONE_BACKWARDS
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 5d06f75ffad4..95b7688341c5 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -143,8 +143,6 @@  static inline void prefetchw(const void *ptr)
 #endif
 #endif
 
-#define HAVE_ARCH_PICK_MMAP_LAYOUT
-
 #endif
 
 #endif /* __ASM_ARM_PROCESSOR_H */
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 72cc0862a30e..19a765db5f7f 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -322,11 +322,6 @@  unsigned long get_wchan(struct task_struct *p)
 	return 0;
 }
 
-unsigned long arch_randomize_brk(struct mm_struct *mm)
-{
-	return randomize_page(mm->brk, 0x02000000);
-}
-
 #ifdef CONFIG_MMU
 #ifdef CONFIG_KUSER_HELPERS
 /*
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index 0b94b674aa91..b8d912ac9e61 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -17,43 +17,6 @@ 
 	((((addr)+SHMLBA-1)&~(SHMLBA-1)) +	\
 	 (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
 
-/* gap between mmap and stack */
-#define MIN_GAP		(128*1024*1024UL)
-#define MAX_GAP		((STACK_TOP)/6*5)
-#define STACK_RND_MASK	(0x7ff >> (PAGE_SHIFT - 12))
-
-static int mmap_is_legacy(struct rlimit *rlim_stack)
-{
-	if (current->personality & ADDR_COMPAT_LAYOUT)
-		return 1;
-
-	if (rlim_stack->rlim_cur == RLIM_INFINITY)
-		return 1;
-
-	return sysctl_legacy_va_layout;
-}
-
-static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
-{
-	unsigned long gap = rlim_stack->rlim_cur;
-	unsigned long pad = stack_guard_gap;
-
-	/* Account for stack randomization if necessary */
-	if (current->flags & PF_RANDOMIZE)
-		pad += (STACK_RND_MASK << PAGE_SHIFT);
-
-	/* Values close to RLIM_INFINITY can overflow. */
-	if (gap + pad > gap)
-		gap += pad;
-
-	if (gap < MIN_GAP)
-		gap = MIN_GAP;
-	else if (gap > MAX_GAP)
-		gap = MAX_GAP;
-
-	return PAGE_ALIGN(STACK_TOP - gap - rnd);
-}
-
 /*
  * We need to ensure that shared mappings are correctly aligned to
  * avoid aliasing issues with VIPT caches.  We need to ensure that
@@ -181,31 +144,6 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	return addr;
 }
 
-unsigned long arch_mmap_rnd(void)
-{
-	unsigned long rnd;
-
-	rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
-
-	return rnd << PAGE_SHIFT;
-}
-
-void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
-{
-	unsigned long random_factor = 0UL;
-
-	if (current->flags & PF_RANDOMIZE)
-		random_factor = arch_mmap_rnd();
-
-	if (mmap_is_legacy(rlim_stack)) {
-		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
-		mm->get_unmapped_area = arch_get_unmapped_area;
-	} else {
-		mm->mmap_base = mmap_base(random_factor, rlim_stack);
-		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
-	}
-}
-
 /*
  * You really shouldn't be using read() or write() on /dev/mem.  This
  * might go away in the future.