| Message ID | 20230803151609.22141-1-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [PATCHv2] x86/mm: Fix VDSO and VVAR placement on 5-level paging machines | expand |
On Thu, 2023-08-03 at 18:16 +0300, Kirill A. Shutemov wrote: > 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. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Reported-by: Yingcong Wu <yingcong.wu@intel.com> > Fixes: b569bab78d8d ("x86/mm: Prepare to expose larger address space > to userspace") Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c index 11a5c68d1218..7645730dc228 100644 --- a/arch/x86/entry/vdso/vma.c +++ b/arch/x86/entry/vdso/vma.c @@ -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) {
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. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Yingcong Wu <yingcong.wu@intel.com> Fixes: b569bab78d8d ("x86/mm: Prepare to expose larger address space to userspace") --- v2: - Fix commit message: grammar and passive voice arch/x86/entry/vdso/vma.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)