arm: use generic mmap top-down layout and brk randomization

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.

Note that it is safe to remove STACK_RND_MASK since it matches the default
value.

Link: http://lkml.kernel.org/r/20190730055113.23635-9-alex@ghiti.fr
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Hogan <jhogan@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 229f2cd..8a50efb 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -34,6 +34,7 @@ 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 BINFMT_FLAT_ARGVP_ENVP_ON_STACK
        select BUILDTIME_EXTABLE_SORT if MMU

diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 20c2f42..614bf82 100644 (file)
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -140,8 +140,6 @@ 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 f934a67..9485acc 100644 (file)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -319,11 +319,6 @@ 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 0b94b67..b8d912a 100644 (file)
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -17,43 +17,6 @@
        ((((addr)+SHMLBA-1)&~(SHMLBA-1)) +      \
         (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
 
-/* 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.