[PATCH v2 1/3] sparc64: Start bottom-up mmap searches at mm->mmap_base

[Stian Halseth <stian@itx.no>]

arch_pick_mmap_layout() randomizes mm->mmap_base for the bottom-up
layout, which every 64-bit task uses, but arch_get_unmapped_area()
starts its search at TASK_UNMAPPED_BASE and never looks at it. Shared
libraries and anonymous mappings of 64-bit tasks therefore land at the
same address on every run; only the stack is randomized.

Before the conversion to vm_unmapped_area() the search started at
mm->free_area_cache, which binfmt_elf set to mm->mmap_base. Use
mm->mmap_base as the low limit again, as generic_get_unmapped_area()
does.

Fixes: bb64f55019c7 ("mm: use vm_unmapped_area() on sparc64 architecture")
Link: https://github.com/sparclinux/issues/issues/119
Cc: stable@vger.kernel.org
Tested-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Stian Halseth <stian@itx.no>
---
 arch/sparc/kernel/sys_sparc_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
index ecefcffcf7b10..087595fa43081 100644
--- a/arch/sparc/kernel/sys_sparc_64.c
+++ b/arch/sparc/kernel/sys_sparc_64.c
@@ -142,7 +142,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
 	}
 
 	info.length = len;
-	info.low_limit = TASK_UNMAPPED_BASE;
+	info.low_limit = mm->mmap_base;
 	info.high_limit = min(task_size, VA_EXCLUDE_START);
 	info.align_mask = get_align_mask(filp, flags);
 	if (!file_hugepage)
@@ -151,7 +151,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
 
 	if ((addr & ~PAGE_MASK) && task_size > VA_EXCLUDE_END) {
 		VM_BUG_ON(addr != -ENOMEM);
-		info.low_limit = VA_EXCLUDE_END;
+		info.low_limit = max(mm->mmap_base, VA_EXCLUDE_END);
 		info.high_limit = task_size;
 		addr = vm_unmapped_area(&info);
 	}
-- 
2.43.0