From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> The "normal" kernel page table creation mechanisms using PAGE_KERNEL_* page protections will never set _PAGE_GLOBAL with PTI. The few places in the kernel that always want _PAGE_GLOBAL must avoid using PAGE_KERNEL_*. Document that we want it here and its use is not accidental. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: x86@xxxxxxxxxx Cc: Nadav Amit <namit@xxxxxxxxxx> --- b/arch/x86/kernel/espfix_64.c | 4 ++++ 1 file changed, 4 insertions(+) diff -puN arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported arch/x86/kernel/espfix_64.c --- a/arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported 2018-03-21 16:31:57.951192318 -0700 +++ b/arch/x86/kernel/espfix_64.c 2018-03-21 16:31:57.954192318 -0700 @@ -195,6 +195,10 @@ void init_espfix_ap(int cpu) pte_p = pte_offset_kernel(&pmd, addr); stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0)); + /* + * __PAGE_KERNEL_* includes _PAGE_GLOBAL, which we want since + * this is mapped to userspace. + */ pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask)); for (n = 0; n < ESPFIX_PTE_CLONES; n++) set_pte(&pte_p[n*PTE_STRIDE], pte); _
