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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q17sm480361pfq.74.2019.05.29.12.26.12 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 29 May 2019 12:26:12 -0700 (PDT) Date: Wed, 29 May 2019 12:26:11 -0700 From: Kees Cook To: Alexandre Ghiti 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 Subject: Re: [PATCH v4 08/14] arm: Use generic mmap top-down layout and brk randomization Message-ID: <201905291222.595685C3F0@keescook> References: <20190526134746.9315-1-alex@ghiti.fr> <20190526134746.9315-9-alex@ghiti.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190526134746.9315-9-alex@ghiti.fr> Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org 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. -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 > -- Kees Cook