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 <[email protected]>
Reported-by: Yingcong Wu <[email protected]>
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(-)
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) {
--
2.41.0
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 <[email protected]>
> Reported-by: Yingcong Wu <[email protected]>
> Fixes: b569bab78d8d ("x86/mm: Prepare to expose larger address space
> to userspace")
Reviewed-by: Rick Edgecombe <[email protected]>