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From: Kees Cook <keescook@chromium.org>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <paul.burton@mips.com>,
	James Hogan <jhogan@kernel.org>,
	Palmer Dabbelt <palmer@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Luis Chamberlain <mcgrof@kernel.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH v4 08/14] arm: Use generic mmap top-down layout and brk randomization
Date: Wed, 29 May 2019 12:26:11 -0700	[thread overview]
Message-ID: <201905291222.595685C3F0@keescook> (raw)
In-Reply-To: <20190526134746.9315-9-alex@ghiti.fr>

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
> 

-- 
Kees Cook

  reply	other threads:[~2019-05-29 19:26 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-26 13:47 [PATCH v4 00/14] Provide generic top-down mmap layout functions Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 01/14] mm, fs: Move randomize_stack_top from fs to mm Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 02/14] arm64: Make use of is_compat_task instead of hardcoding this test Alexandre Ghiti
2019-06-03 17:32   ` Catalin Marinas
2019-05-26 13:47 ` [PATCH v4 03/14] arm64: Consider stack randomization for mmap base only when necessary Alexandre Ghiti
2019-06-03 17:37   ` Catalin Marinas
2019-05-26 13:47 ` [PATCH v4 04/14] arm64, mm: Move generic mmap layout functions to mm Alexandre Ghiti
2019-05-29 20:10   ` Kees Cook
2019-06-03 17:38   ` Catalin Marinas
2019-05-26 13:47 ` [PATCH v4 05/14] arm64, mm: Make randomization selected by generic topdown mmap layout Alexandre Ghiti
2019-05-29 20:10   ` Kees Cook
2019-06-01  9:04   ` Christoph Hellwig
2019-06-03  7:05     ` Alexandre Ghiti
2019-06-03 17:40   ` Catalin Marinas
2019-06-04  6:20     ` Alex Ghiti
2019-05-26 13:47 ` [PATCH v4 06/14] arm: Properly account for stack randomization and stack guard gap Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 07/14] arm: Use STACK_TOP when computing mmap base address Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 08/14] arm: Use generic mmap top-down layout and brk randomization Alexandre Ghiti
2019-05-29 19:26   ` Kees Cook [this message]
2019-05-31  4:49     ` Alex Ghiti
2019-05-26 13:47 ` [PATCH v4 09/14] mips: Properly account for stack randomization and stack guard gap Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 10/14] mips: Use STACK_TOP when computing mmap base address Alexandre Ghiti
2019-05-26 13:47 ` [PATCH v4 11/14] mips: Adjust brk randomization offset to fit generic version Alexandre Ghiti
2019-05-29 20:12   ` Kees Cook
2019-05-26 13:47 ` [PATCH v4 12/14] mips: Replace arch specific way to determine 32bit task with " Alexandre Ghiti
2019-05-29 20:12   ` Kees Cook
2019-05-26 13:47 ` [PATCH v4 13/14] mips: Use generic mmap top-down layout and brk randomization Alexandre Ghiti
2019-05-29 20:12   ` Kees Cook
2019-05-26 13:47 ` [PATCH v4 14/14] riscv: Make mmap allocation top-down by default Alexandre Ghiti
2019-05-29 20:16 ` [PATCH v4 00/14] Provide generic top-down mmap layout functions Kees Cook
2019-05-31  5:04   ` Alex Ghiti
2019-06-13  5:29 ` Alex Ghiti
2019-06-30 15:34   ` Alex Ghiti

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