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Subject[PATCH] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border
Date
In case of 5-level paging, we don't put any mapping above 47-bit, unless
userspace explicitly asked for it.

Userspace can ask for allocation from full address space by specifying
hint address above 47-bit.

Nicholas noticed that current implementation violates this interface:
we can get vma partly in high addresses if we ask for a mapping at very
end of 47-bit address space.

Let's make sure that, when consider hint address for non-MAP_FIXED
mapping, start and end of resulting vma are on the same side of 47-bit
border.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/x86/kernel/sys_x86_64.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index a63fe77b3217..64b1a0d22247 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -198,11 +198,19 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
/* requesting a specific address */
if (addr) {
addr = PAGE_ALIGN(addr);
+ if (TASK_SIZE - len < addr)
+ goto get_unmapped_area;
+
+ /* The mapping shouldn't cross DEFAULT_MAP_WINDOW border */
+ if ((addr > DEFAULT_MAP_WINDOW) !=
+ (addr + len > DEFAULT_MAP_WINDOW))
+ goto get_unmapped_area;
+
vma = find_vma(mm, addr);
- if (TASK_SIZE - len >= addr &&
- (!vma || addr + len <= vm_start_gap(vma)))
+ if (!vma || addr + len <= vm_start_gap(vma))
return addr;
}
+get_unmapped_area:

info.flags = VM_UNMAPPED_AREA_TOPDOWN;
info.length = len;
--
2.14.2
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