On Mon, 2023-02-20 at 13:58 +0100, David Hildenbrand wrote: > On 18.02.23 22:14, Rick Edgecombe wrote: > > From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> > > > > The x86 Control-flow Enforcement Technology (CET) feature includes > > a new > > type of memory called shadow stack. This shadow stack memory has > > some > > unusual properties, which requires some core mm changes to function > > properly. > > > > Account shadow stack pages to stack memory. > > > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> > > Tested-by: John Allen <john.allen@xxxxxxx> > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> > > Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > > > --- > > v3: > > - Remove unneeded VM_SHADOW_STACK check in accountable_mapping() > > (Kirill) > > > > v2: > > - Remove is_shadow_stack_mapping() and just change it to > > directly bitwise > > and VM_SHADOW_STACK. > > > > Yu-cheng v26: > > - Remove redundant #ifdef CONFIG_MMU. > > > > Yu-cheng v25: > > - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for > > is_shadow_stack_mapping(). > > --- > > mm/mmap.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 425a9349e610..9f85596cce31 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -3290,6 +3290,8 @@ void vm_stat_account(struct mm_struct *mm, > > vm_flags_t flags, long npages) > > mm->exec_vm += npages; > > else if (is_stack_mapping(flags)) > > mm->stack_vm += npages; > > + else if (flags & VM_SHADOW_STACK) > > + mm->stack_vm += npages; > > Why not modify is_stack_mapping() ? It kind of sticks out a little in this conditional, but is_stack_mapping() has this comment: /* * Stack area - automatically grows in one direction * * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous: * do_mmap() forbids all other combinations. */ Shadow stack don't grow, so it doesn't quite fit. There used to be an is_shadow_stack_mapping(), but it was removed because all that was needed (for the time being) was the simple bitwise AND: https://lore.kernel.org/lkml/804adbac-61e6-0fd2-f726-5735fb290199@xxxxxxxxx/
