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[217.70.178.231]) by mx.google.com with ESMTPS id m18si3140560ejq.1.2019.05.30.21.49.56 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 30 May 2019 21:49:56 -0700 (PDT) Received-SPF: neutral (google.com: 217.70.178.231 is neither permitted nor denied by best guess record for domain of alex@ghiti.fr) client-ip=217.70.178.231; Authentication-Results: mx.google.com; spf=neutral (google.com: 217.70.178.231 is neither permitted nor denied by best guess record for domain of alex@ghiti.fr) smtp.mailfrom=alex@ghiti.fr Received: from [192.168.0.12] (127.19.86.79.rev.sfr.net [79.86.19.127]) (Authenticated sender: alex@ghiti.fr) by relay11.mail.gandi.net (Postfix) with ESMTPSA id 18921100004; Fri, 31 May 2019 04:49:29 +0000 (UTC) Subject: Re: [PATCH v4 08/14] arm: Use generic mmap top-down layout and brk randomization To: Kees Cook Cc: Andrew Morton , Christoph Hellwig , Russell King , Catalin Marinas , Will Deacon , Ralf Baechle , Paul Burton , James Hogan , Palmer Dabbelt , Albert Ou , Alexander Viro , Luis Chamberlain , 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 References: <20190526134746.9315-1-alex@ghiti.fr> <20190526134746.9315-9-alex@ghiti.fr> <201905291222.595685C3F0@keescook> From: Alex Ghiti Message-ID: Date: Fri, 31 May 2019 00:49:29 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <201905291222.595685C3F0@keescook> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Content-Language: sv-FI X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > Acked-by: Kees Cook > > 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)<> >> -/* 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 >>