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Date:   Wed, 29 May 2019 13:10:34 -0700
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,
        Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v4 04/14] arm64, mm: Move generic mmap layout functions
 to mm
Message-ID: <201905291310.D7E954C95B@keescook>
References: <20190526134746.9315-1-alex@ghiti.fr>
 <20190526134746.9315-5-alex@ghiti.fr>
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On Sun, May 26, 2019 at 09:47:36AM -0400, Alexandre Ghiti wrote:
> arm64 handles top-down mmap layout in a way that can be easily reused
> by other architectures, so make it available in mm.
> It then introduces a new config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> that can be set by other architectures to benefit from those functions.
> Note that this new config depends on MMU being enabled, if selected
> without MMU support, a warning will be thrown.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

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

-Kees

> ---
>  arch/Kconfig                       | 10 ++++
>  arch/arm64/Kconfig                 |  1 +
>  arch/arm64/include/asm/processor.h |  2 -
>  arch/arm64/mm/mmap.c               | 76 -----------------------------
>  kernel/sysctl.c                    |  6 ++-
>  mm/util.c                          | 78 +++++++++++++++++++++++++++++-
>  6 files changed, 92 insertions(+), 81 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index c47b328eada0..df3ab04270fa 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -701,6 +701,16 @@ config HAVE_ARCH_COMPAT_MMAP_BASES
>  	  and vice-versa 32-bit applications to call 64-bit mmap().
>  	  Required for applications doing different bitness syscalls.
>  
> +# This allows to use a set of generic functions to determine mmap base
> +# address by giving priority to top-down scheme only if the process
> +# is not in legacy mode (compat task, unlimited stack size or
> +# sysctl_legacy_va_layout).
> +# Architecture that selects this option can provide its own version of:
> +# - STACK_RND_MASK
> +config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> +	bool
> +	depends on MMU
> +
>  config HAVE_COPY_THREAD_TLS
>  	bool
>  	help
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4780eb7af842..3d754c19c11e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -69,6 +69,7 @@ config ARM64
>  	select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 50000 || CC_IS_CLANG
>  	select ARCH_SUPPORTS_NUMA_BALANCING
>  	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
> +	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>  	select ARCH_WANT_FRAME_POINTERS
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARM_AMBA
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index fcd0e691b1ea..3bd818edf319 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -282,8 +282,6 @@ static inline void spin_lock_prefetch(const void *ptr)
>  		     "nop") : : "p" (ptr));
>  }
>  
> -#define HAVE_ARCH_PICK_MMAP_LAYOUT
> -
>  #endif
>  
>  extern unsigned long __ro_after_init signal_minsigstksz; /* sigframe size */
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index ac89686c4af8..c74224421216 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -31,82 +31,6 @@
>  
>  #include <asm/cputype.h>
>  
> -/*
> - * Leave enough space between the mmap area and the stack to honour ulimit in
> - * the face of randomisation.
> - */
> -#define MIN_GAP (SZ_128M)
> -#define MAX_GAP	(STACK_TOP/6*5)
> -
> -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;
> -}
> -
> -unsigned long arch_mmap_rnd(void)
> -{
> -	unsigned long rnd;
> -
> -#ifdef CONFIG_COMPAT
> -	if (is_compat_task())
> -		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
> -	else
> -#endif
> -		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> -	return rnd << PAGE_SHIFT;
> -}
> -
> -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);
> -}
> -
> -/*
> - * This function, called very early during the creation of a new process VM
> - * image, sets up which VM layout function to use:
> - */
> -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();
> -
> -	/*
> -	 * Fall back to the standard layout if the personality bit is set, or
> -	 * if the expected stack growth is unlimited:
> -	 */
> -	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.
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 943c89178e3d..aebd03cc4b65 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -271,7 +271,8 @@ extern struct ctl_table epoll_table[];
>  extern struct ctl_table firmware_config_table[];
>  #endif
>  
> -#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
> +#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
> +    defined(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
>  int sysctl_legacy_va_layout;
>  #endif
>  
> @@ -1566,7 +1567,8 @@ static struct ctl_table vm_table[] = {
>  		.proc_handler	= proc_dointvec,
>  		.extra1		= &zero,
>  	},
> -#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
> +#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
> +    defined(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
>  	{
>  		.procname	= "legacy_va_layout",
>  		.data		= &sysctl_legacy_va_layout,
> diff --git a/mm/util.c b/mm/util.c
> index dab33b896146..717f5d75c16e 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -15,7 +15,12 @@
>  #include <linux/vmalloc.h>
>  #include <linux/userfaultfd_k.h>
>  #include <linux/elf.h>
> +#include <linux/elf-randomize.h>
> +#include <linux/personality.h>
>  #include <linux/random.h>
> +#include <linux/processor.h>
> +#include <linux/sizes.h>
> +#include <linux/compat.h>
>  
>  #include <linux/uaccess.h>
>  
> @@ -313,7 +318,78 @@ unsigned long randomize_stack_top(unsigned long stack_top)
>  #endif
>  }
>  
> -#if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
> +#ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> +#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
> +unsigned long arch_mmap_rnd(void)
> +{
> +	unsigned long rnd;
> +
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
> +	if (is_compat_task())
> +		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
> +	else
> +#endif /* CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS */
> +		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> +
> +	return rnd << PAGE_SHIFT;
> +}
> +#endif /* CONFIG_ARCH_HAS_ELF_RANDOMIZE */
> +
> +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;
> +}
> +
> +/*
> + * Leave enough space between the mmap area and the stack to honour ulimit in
> + * the face of randomisation.
> + */
> +#define MIN_GAP		(SZ_128M)
> +#define MAX_GAP		(STACK_TOP / 6 * 5)
> +
> +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);
> +}
> +
> +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;
> +	}
> +}
> +#elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
>  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>  {
>  	mm->mmap_base = TASK_UNMAPPED_BASE;
> -- 
> 2.20.1
> 

-- 
Kees Cook