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. In change_pte_range(), when a PTE is changed for prot_numa, _PAGE_RW is preserved to avoid the additional write fault after the NUMA hinting fault. However, pte_write() now includes both normal writable and shadow stack (Write=0, Dirty=1) PTEs, but the latter does not have _PAGE_RW and has no need to preserve it. Exclude shadow stack from preserve_write test, and apply the same change to change_huge_pmd(). Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> Tested-by: John Allen <john.allen@xxxxxxx> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> --- Yu-cheng v25: - Move is_shadow_stack_mapping() to a separate line. Yu-cheng v24: - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping(). mm/huge_memory.c | 7 +++++++ mm/mprotect.c | 7 +++++++ 2 files changed, 14 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 73b9b78f8cf4..7643a4db1b50 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1803,6 +1803,13 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, return 0; preserve_write = prot_numa && pmd_write(*pmd); + + /* + * Preserve only normal writable huge PMD, but not shadow + * stack (RW=0, Dirty=1). + */ + if (vma->vm_flags & VM_SHADOW_STACK) + preserve_write = false; ret = 1; #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION diff --git a/mm/mprotect.c b/mm/mprotect.c index 668bfaa6ed2a..ea82ce5f38fe 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -115,6 +115,13 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, pte_t ptent; bool preserve_write = prot_numa && pte_write(oldpte); + /* + * Preserve only normal writable PTE, but not shadow + * stack (RW=0, Dirty=1). + */ + if (vma->vm_flags & VM_SHADOW_STACK) + preserve_write = false; + /* * Avoid trapping faults against the zero or KSM * pages. See similar comment in change_huge_pmd. -- 2.17.1
