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[PATCH 2/4] arm: mm: support ARCH_MMAP_RND_BITS.

Started byDaniel Cashman <dcashman@android.com>
First post2015-11-18 23:50 +0100
Last post2015-11-19 00:30 +0100
Articles 4 — 2 participants

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  [PATCH 2/4] arm: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-11-18 23:50 +0100
    [PATCH 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-11-18 23:50 +0100
      [PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-11-18 23:50 +0100
        Re: [PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS. Kees Cook <keescook@chromium.org> - 2015-11-19 00:30 +0100

#1272645 — [PATCH 2/4] arm: mm: support ARCH_MMAP_RND_BITS.

FromDaniel Cashman <dcashman@android.com>
Date2015-11-18 23:50 +0100
Subject[PATCH 2/4] arm: mm: support ARCH_MMAP_RND_BITS.
Message-ID<qwjI5-Vr-1@gated-at.bofh.it>
From: dcashman <dcashman@google.com>

arm: arch_mmap_rnd() uses a hard-code value of 8 to generate the
random offset for the mmap base address.  This value represents a
compromise between increased ASLR effectiveness and avoiding
address-space fragmentation. Replace it with a Kconfig option, which
is sensibly bounded, so that platform developers may choose where to
place this compromise. Keep 8 as the minimum acceptable value.

Signed-off-by: Daniel Cashman <dcashman@google.com>
---
 arch/arm/Kconfig   | 10 ++++++++++
 arch/arm/mm/mmap.c |  3 +--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0365cbb..ca2e43a 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -35,6 +35,7 @@ config ARM
 	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
 	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32
 	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32
+	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT)
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_BPF_JIT
@@ -306,6 +307,15 @@ config MMU
 	  Select if you want MMU-based virtualised addressing space
 	  support by paged memory management. If unsure, say 'Y'.
 
+config ARCH_MMAP_RND_BITS_MIN
+	default 8
+
+config ARCH_MMAP_RND_BITS_MAX
+	default 14 if MMU && PAGE_OFFSET=0x40000000
+	default 15 if MMU && PAGE_OFFSET=0x80000000
+	default 16 if MMU
+	default 8
+
 #
 # The "ARM system type" choice list is ordered alphabetically by option
 # text.  Please add new entries in the option alphabetic order.
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index 407dc78..c938693 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -173,8 +173,7 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-	/* 8 bits of randomness in 20 address space bits */
-	rnd = (unsigned long)get_random_int() % (1 << 8);
+	rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
 
 	return rnd << PAGE_SHIFT;
 }
-- 
2.6.0.rc2.230.g3dd15c0

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#1272646 — [PATCH 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.

FromDaniel Cashman <dcashman@android.com>
Date2015-11-18 23:50 +0100
Subject[PATCH 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.
Message-ID<qwjI6-Vr-15@gated-at.bofh.it>
In reply to#1272645
From: dcashman <dcashman@google.com>

arm64: arch_mmap_rnd() uses STACK_RND_MASK to generate the
random offset for the mmap base address.  This value represents a
compromise between increased ASLR effectiveness and avoiding
address-space fragmentation. Replace it with a Kconfig option, which
is sensibly bounded, so that platform developers may choose where to
place this compromise. Keep default values as new minimums.

Signed-off-by: Daniel Cashman <dcashman@google.com>
---
 arch/arm64/Kconfig   | 23 +++++++++++++++++++++++
 arch/arm64/mm/mmap.c |  6 ++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9ac16a4..be38e4c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -51,6 +51,8 @@ config ARM64
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_KASAN if SPARSEMEM_VMEMMAP
 	select HAVE_ARCH_KGDB
+	select HAVE_ARCH_MMAP_RND_BITS
+	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_BPF_JIT
@@ -104,6 +106,27 @@ config ARCH_PHYS_ADDR_T_64BIT
 config MMU
 	def_bool y
 
+config ARCH_MMAP_RND_BITS_MIN
+       default 15 if ARM64_64K_PAGES
+       default 19
+
+config ARCH_MMAP_RND_BITS_MAX
+       default 20 if ARM64_64K_PAGES && ARCH_VA_BITS=39
+       default 24 if ARCH_VA_BITS=39
+       default 23 if ARM64_64K_PAGES && ARCH_VA_BITS=42
+       default 27 if ARCH_VA_BITS=42
+       default 29 if ARM64_64K_PAGES && ARCH_VA_BITS=48
+       default 33 if ARCH_VA_BITS=48
+       default 15 if ARM64_64K_PAGES
+       default 19
+
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+       default 7 if ARM64_64K_PAGES
+       default 11
+
+config ARCH_MMAP_RND_COMPAT_BITS_MAX
+       default 16
+
 config NO_IOPORT_MAP
 	def_bool y if !PCI
 
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index ed17747..b84d5b1 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -51,8 +51,10 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-	rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
-
+	if (test_thread_flag(TIF_32BIT))
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
+	else
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
 	return rnd << PAGE_SHIFT;
 }
 
-- 
2.6.0.rc2.230.g3dd15c0

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#1272648 — [PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS.

FromDaniel Cashman <dcashman@android.com>
Date2015-11-18 23:50 +0100
Subject[PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS.
Message-ID<qwjI6-Vr-19@gated-at.bofh.it>
In reply to#1272646
From: dcashman <dcashman@google.com>

x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for
64-bit, to generate the random offset for the mmap base address.
This value represents a compromise between increased ASLR
effectiveness and avoiding address-space fragmentation. Replace it
with a Kconfig option, which is sensibly bounded, so that platform
developers may choose where to place this compromise. Keep default
values as new minimums.

Signed-off-by: Daniel Cashman <dcashman@google.com>
---
 arch/x86/Kconfig   | 16 ++++++++++++++++
 arch/x86/mm/mmap.c | 12 ++++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index db3622f..12768c4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -82,6 +82,8 @@ config X86
 	select HAVE_ARCH_KASAN			if X86_64 && SPARSEMEM_VMEMMAP
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_KMEMCHECK
+	select HAVE_ARCH_MMAP_RND_BITS
+	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_SOFT_DIRTY		if X86_64
 	select HAVE_ARCH_TRACEHOOK
@@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT
 config MMU
 	def_bool y
 
+config ARCH_MMAP_RND_BITS_MIN
+       default 28 if 64BIT
+       default 8
+
+config ARCH_MMAP_RND_BITS_MAX
+	default 32 if 64BIT
+	default 16
+
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+	default 8
+
+config ARCH_MMAP_RND_COMPAT_BITS_MAX
+	default 16
+
 config SBUS
 	bool
 
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 844b06d..647fecf 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-	/*
-	 *  8 bits of randomness in 32bit mmaps, 20 address space bits
-	 * 28 bits of randomness in 64bit mmaps, 40 address space bits
-	 */
 	if (mmap_is_ia32())
-		rnd = (unsigned long)get_random_int() % (1<<8);
+#ifdef CONFIG_COMPAT
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
+#else
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
+#endif
 	else
-		rnd = (unsigned long)get_random_int() % (1<<28);
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
 
 	return rnd << PAGE_SHIFT;
 }
-- 
2.6.0.rc2.230.g3dd15c0

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#1272682 — Re: [PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS.

FromKees Cook <keescook@chromium.org>
Date2015-11-19 00:30 +0100
SubjectRe: [PATCH 4/4] x86: mm: support ARCH_MMAP_RND_BITS.
Message-ID<qwkkP-1pG-47@gated-at.bofh.it>
In reply to#1272648
On Wed, Nov 18, 2015 at 2:48 PM, Daniel Cashman <dcashman@android.com> wrote:
> From: dcashman <dcashman@google.com>
>
> x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for
> 64-bit, to generate the random offset for the mmap base address.
> This value represents a compromise between increased ASLR
> effectiveness and avoiding address-space fragmentation. Replace it
> with a Kconfig option, which is sensibly bounded, so that platform
> developers may choose where to place this compromise. Keep default
> values as new minimums.
>
> Signed-off-by: Daniel Cashman <dcashman@google.com>
> ---
>  arch/x86/Kconfig   | 16 ++++++++++++++++
>  arch/x86/mm/mmap.c | 12 ++++++------
>  2 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index db3622f..12768c4 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -82,6 +82,8 @@ config X86
>         select HAVE_ARCH_KASAN                  if X86_64 && SPARSEMEM_VMEMMAP
>         select HAVE_ARCH_KGDB
>         select HAVE_ARCH_KMEMCHECK
> +       select HAVE_ARCH_MMAP_RND_BITS
> +       select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>         select HAVE_ARCH_SECCOMP_FILTER
>         select HAVE_ARCH_SOFT_DIRTY             if X86_64
>         select HAVE_ARCH_TRACEHOOK
> @@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT
>  config MMU
>         def_bool y
>
> +config ARCH_MMAP_RND_BITS_MIN
> +       default 28 if 64BIT
> +       default 8
> +
> +config ARCH_MMAP_RND_BITS_MAX
> +       default 32 if 64BIT
> +       default 16
> +
> +config ARCH_MMAP_RND_COMPAT_BITS_MIN
> +       default 8
> +
> +config ARCH_MMAP_RND_COMPAT_BITS_MAX
> +       default 16
> +
>  config SBUS
>         bool
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 844b06d..647fecf 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void)
>  {
>         unsigned long rnd;
>
> -       /*
> -        *  8 bits of randomness in 32bit mmaps, 20 address space bits
> -        * 28 bits of randomness in 64bit mmaps, 40 address space bits
> -        */
>         if (mmap_is_ia32())
> -               rnd = (unsigned long)get_random_int() % (1<<8);
> +#ifdef CONFIG_COMPAT
> +               rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
> +#else
> +               rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
> +#endif

Oh, that is a weird side-effect of x86's compat: a 32-bit build isn't
compat, so it needs the native bits. I'm trying to resist bikeshedding
the names again, so probably this should stay as-is.

-Kees

>         else
> -               rnd = (unsigned long)get_random_int() % (1<<28);
> +               rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
>
>         return rnd << PAGE_SHIFT;
>  }
> --
> 2.6.0.rc2.230.g3dd15c0
>



-- 
Kees Cook
Chrome OS Security
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