From ae1f05a617dcbc0a732fbeba0893786cd009536c Mon Sep 17 00:00:00 2001 From: Rick Edgecombe Date: Mon, 12 Jun 2023 17:10:44 -0700 Subject: [PATCH] x86/mm: Warn if create Write=0,Dirty=1 with raw prot When user shadow stack is in use, Write=0,Dirty=1 is treated by the CPU as shadow stack memory. So for shadow stack memory this bit combination is valid, but when Dirty=1,Write=1 (conventionally writable) memory is being write protected, the kernel has been taught to transition the Dirty=1 bit to SavedDirty=1, to avoid inadvertently creating shadow stack memory. It does this inside pte_wrprotect() because it knows the PTE is not intended to be a writable shadow stack entry, it is supposed to be write protected. However, when a PTE is created by a raw prot using mk_pte(), mk_pte() can't know whether to adjust Dirty=1 to SavedDirty=1. It can't distinguish between the caller intending to create a shadow stack PTE or needing the SavedDirty shift. The kernel has been updated to not do this, and so Write=0,Dirty=1 memory should only be created by the pte_mkfoo() helpers. Add a warning to make sure no new mk_pte() start doing this, like, for example, set_memory_rox() did. Signed-off-by: Rick Edgecombe Signed-off-by: Dave Hansen Tested-by: Pengfei Xu Tested-by: John Allen Tested-by: Kees Cook Link: https://lore.kernel.org/all/20230613001108.3040476-19-rick.p.edgecombe%40intel.com --- arch/x86/include/asm/pgtable.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 9255b5b7a9d95..61b52445e4d61 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1033,7 +1033,14 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd) * (Currently stuck as a macro because of indirect forward reference * to linux/mm.h:page_to_nid()) */ -#define mk_pte(page, pgprot) pfn_pte(page_to_pfn(page), (pgprot)) +#define mk_pte(page, pgprot) \ +({ \ + pgprot_t __pgprot = pgprot; \ + \ + WARN_ON_ONCE((pgprot_val(__pgprot) & (_PAGE_DIRTY | _PAGE_RW)) == \ + _PAGE_DIRTY); \ + pfn_pte(page_to_pfn(page), __pgprot); \ +}) static inline int pmd_bad(pmd_t pmd) { -- 2.30.2