Re: [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack memory
From: Kees Cook <hidden>
Date: 2022-10-03 18:39:20
Also in:
linux-arch, linux-doc, linux-mm, lkml
On Thu, Sep 29, 2022 at 03:29:19PM -0700, Rick Edgecombe wrote:
[...] Still allow FOLL_FORCE to write through shadow stack protections, as it does for read-only protections.
As I asked in the cover letter: why do we need to add this for shstk? It was a mistake for general memory. :P
quoted hunk ↗ jump to hunk
[...]diff --git a/mm/gup.c b/mm/gup.c index 5abdaf487460..56da98f3335c 100644 --- a/mm/gup.c +++ b/mm/gup.c@@ -1043,7 +1043,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) return -EFAULT; if (write) { - if (!(vm_flags & VM_WRITE)) { + if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) { if (!(gup_flags & FOLL_FORCE)) return -EFAULT; /*
How about this instead:
return -EFAULT;
if (write) {
+ if (vm_flags & VM_SHADOW_STACK)
+ return -EFAULT;
if (!(vm_flags & VM_WRITE)) {
if (!(gup_flags & FOLL_FORCE))
return -EFAULT;
--
Kees Cook