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. 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. Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> Tested-by: John Allen <john.allen@xxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> --- include/linux/mm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 4650e2580d60..e6f1789c8e69 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -366,7 +366,7 @@ 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 -- 2.17.1
