From mboxrd@z Thu Jan 1 00:00:00 1970 From: dcashman@android.com (Daniel Cashman) Date: Thu, 26 Nov 2015 14:59:43 -0800 Subject: [PATCH v4 2/4] arm: mm: support ARCH_MMAP_RND_BITS. In-Reply-To: <1448578785-17656-2-git-send-email-dcashman@android.com> References: <1448578785-17656-1-git-send-email-dcashman@android.com> <1448578785-17656-2-git-send-email-dcashman@android.com> Message-ID: <1448578785-17656-3-git-send-email-dcashman@android.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 --- 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