[v8,17/40] mm: Move VM_UFFD_MINOR_BIT from 37 to 38

Commit Message

Rick Edgecombe March 19, 2023, 12:15 a.m. UTC

From: Yu-cheng Yu <[e-mail]>

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.

Future patches will introduce a new VM flag VM_SHADOW_STACK that will be
VM_HIGH_ARCH_BIT_5. VM_HIGH_ARCH_BIT_1 through VM_HIGH_ARCH_BIT_4 are
bits 32-36, and bit 37 is the unrelated VM_UFFD_MINOR_BIT. For the sake
of order, make all VM_HIGH_ARCH_BITs stay together by moving
VM_UFFD_MINOR_BIT from 37 to 38. This will allow VM_SHADOW_STACK to be
introduced as 37.

Co-developed-by: Rick Edgecombe <[e-mail]>
Signed-off-by: Yu-cheng Yu <[e-mail]>
Signed-off-by: Rick Edgecombe <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Reviewed-by: Axel Rasmussen <[e-mail]>
Acked-by: Mike Rapoport (IBM) <[e-mail]>
Acked-by: Peter Xu <[e-mail]>
Tested-by: Pengfei Xu <[e-mail]>
Tested-by: John Allen <[e-mail]>
Tested-by: Kees Cook <[e-mail]>
---
 include/linux/mm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

David Hildenbrand March 20, 2023, 10:55 a.m. UTC | #1

On 19.03.23 01:15, Rick Edgecombe wrote:
> From: Yu-cheng Yu <[e-mail]>
> 
> 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.
> 
> Future patches will introduce a new VM flag VM_SHADOW_STACK that will be
> VM_HIGH_ARCH_BIT_5. VM_HIGH_ARCH_BIT_1 through VM_HIGH_ARCH_BIT_4 are
> bits 32-36, and bit 37 is the unrelated VM_UFFD_MINOR_BIT. For the sake
> of order, make all VM_HIGH_ARCH_BITs stay together by moving
> VM_UFFD_MINOR_BIT from 37 to 38. This will allow VM_SHADOW_STACK to be
> introduced as 37.
> 
> Co-developed-by: Rick Edgecombe <[e-mail]>
> Signed-off-by: Yu-cheng Yu <[e-mail]>
> Signed-off-by: Rick Edgecombe <[e-mail]>
> Reviewed-by: Kees Cook <[e-mail]>
> Reviewed-by: Axel Rasmussen <[e-mail]>
> Acked-by: Mike Rapoport (IBM) <[e-mail]>
> Acked-by: Peter Xu <[e-mail]>
> Tested-by: Pengfei Xu <[e-mail]>
> Tested-by: John Allen <[e-mail]>
> Tested-by: Kees Cook <[e-mail]>
> ---


Reviewed-by: David Hildenbrand <[e-mail]>

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index af652444fbba..a1b31caae013 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -377,7 +377,7 @@  extern unsigned int kobjsize(const void *objp);
 #endif
 
 #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
-# define VM_UFFD_MINOR_BIT	37
+# define VM_UFFD_MINOR_BIT	38
 # define VM_UFFD_MINOR		BIT(VM_UFFD_MINOR_BIT)	/* UFFD minor faults */
 #else /* !CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
 # define VM_UFFD_MINOR		VM_NONE