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x86/mm: Fix VDSO and VVAR placement on 5-level paging machines 

Yingcong has noticed that on the 5-level paging machine, VDSO and VVAR
VMAs are placed above the 47-bit border:

8000001a9000-8000001ad000 r--p 00000000 00:00 0                          [vvar]
8000001ad000-8000001af000 r-xp 00000000 00:00 0                          [vdso]

This might confuse users who are not aware of 5-level paging and expect
all userspace addresses to be under the 47-bit border.

So far problem has only been triggered with ASLR disabled, although it
may also occur with ASLR enabled if the layout is randomized in a just
right way.

The problem happens due to custom placement for the VMAs in the VDSO
code: vdso_addr() tries to place them above the stack and checks the
result against TASK_SIZE_MAX, which is wrong. TASK_SIZE_MAX is set to
the 56-bit border on 5-level paging machines. Use DEFAULT_MAP_WINDOW
instead.

Fixes: b569bab78d ("x86/mm: Prepare to expose larger address space to userspace")
Reported-by: Yingcong Wu <yingcong.wu@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20230803151609.22141-1-kirill.shutemov%40linux.intel.com
This commit is contained in:
Kirill A. Shutemov 2023-08-03 18:16:09 +03:00 committed by Dave Hansen
parent 7324f74d39
commit 1b8b1aa90c
1 changed files with 2 additions and 2 deletions
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4
arch/x86/entry/vdso/vma.c
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@ -299,8 +299,8 @@ static unsigned long vdso_addr(unsigned long start, unsigned len)
/* Round the lowest possible end address up to a PMD boundary. */
end = (start + len + PMD_SIZE - 1) & PMD_MASK;
if (end >= TASK_SIZE_MAX)
end = TASK_SIZE_MAX;
if (end >= DEFAULT_MAP_WINDOW)
end = DEFAULT_MAP_WINDOW;
end -= len;
if (end > start) {