Re: [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB Shadow Stack page fault

Kees Cook
2020-02-25T20:59:05Z

On Wed, Feb 05, 2020 at 10:19:23AM -0800, Yu-cheng Yu wrote:
> This patch implements THP Shadow Stack (SHSTK) copying in the same way as
> in the previous patch for regular PTE.
>
> In copy_huge_pmd(), clear the dirty bit from the PMD to cause a page fault
> upon the next SHSTK access to the PMD. At that time, fix the PMD and
> copy/re-use the page.

Now is as good a time as any to ask: do you have selftests for all this?
It seems like it would be really nice to have a way to verify SHSTK is
working correctly.

-Kees

>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> arch/x86/mm/pgtable.c | 8 ++++++++
> include/asm-generic/pgtable.h | 11 +++++++++++
> mm/huge_memory.c | 4 ++++
> 3 files changed, 23 insertions(+)
>
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 2eb33794c08d..3340b1d4e9da 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -886,4 +886,12 @@ inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
> else
> return pte;
> }
> +
> +inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma)
> +{
> + if (vma->vm_flags & VM_SHSTK)
> + return pmd_mkdirty_shstk(pmd);
> + else
> + return pmd;
> +}
> #endif /* CONFIG_X86_INTEL_SHADOW_STACK_USER */
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 9cb2f9ba5895..a9df093fdf45 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -1201,9 +1201,20 @@ static inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
> {
> return pte;
> }
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma)
> +{
> + return pmd;
> +}
> +#endif
> #else
> bool arch_copy_pte_mapping(vm_flags_t vm_flags);
> pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma);
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma);
> +#endif
> #endif
> #endif /* CONFIG_MMU */
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a88093213674..93ef368df2dd 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -636,6 +636,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>
> entry = mk_huge_pmd(page, vma->vm_page_prot);
> entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> + entry = pmd_set_vma_features(entry, vma);
> page_add_new_anon_rmap(page, vma, haddr, true);
> mem_cgroup_commit_charge(page, memcg, false, true);
> lru_cache_add_active_or_unevictable(page, vma);
> @@ -1278,6 +1279,7 @@ static vm_fault_t do_huge_pmd_wp_page_fallback(struct vm_fault *vmf,
> pte_t entry;
> entry = mk_pte(pages[i], vma->vm_page_prot);
> entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> + entry = pte_set_vma_features(entry, vma);
> memcg = (void *)page_private(pages[i]);
> set_page_private(pages[i], 0);
> page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
> @@ -1360,6 +1362,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
> pmd_t entry;
> entry = pmd_mkyoung(orig_pmd);
> entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> + entry = pmd_set_vma_features(entry, vma);
> if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry, 1))
> update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
> ret |= VM_FAULT_WRITE;
> @@ -1432,6 +1435,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
> pmd_t entry;
> entry = mk_huge_pmd(new_page, vma->vm_page_prot);
> entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> + entry = pmd_set_vma_features(entry, vma);
> pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
> page_add_new_anon_rmap(new_page, vma, haddr, true);
> mem_cgroup_commit_charge(new_page, memcg, false, true);
> --
> 2.21.0
>

--
Kees Cook