diff --git a/debian/changelog b/debian/changelog index ffa6908a2..32e5f5c02 100644 --- a/debian/changelog +++ b/debian/changelog @@ -442,6 +442,7 @@ linux (4.18.14-1) UNRELEASED; urgency=medium [ Salvatore Bonaccorso ] * [x86] swiotlb: Enable swiotlb for > 4GiG RAM on 32-bit kernels (Closes: #908924) + * mremap: properly flush TLB before releasing the page (CVE-2018-18281) -- Ben Hutchings Mon, 08 Oct 2018 19:02:53 +0100 diff --git a/debian/patches/bugfix/all/mremap-properly-flush-TLB-before-releasing-the-page.patch b/debian/patches/bugfix/all/mremap-properly-flush-TLB-before-releasing-the-page.patch new file mode 100644 index 000000000..68131a77f --- /dev/null +++ b/debian/patches/bugfix/all/mremap-properly-flush-TLB-before-releasing-the-page.patch @@ -0,0 +1,175 @@ +From: Linus Torvalds +Date: Fri, 12 Oct 2018 15:22:59 -0700 +Subject: mremap: properly flush TLB before releasing the page +Origin: https://git.kernel.org/linus/eb66ae030829605d61fbef1909ce310e29f78821 +Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2018-18281 +Bug: https://bugs.chromium.org/p/project-zero/issues/detail?id=1695 + +Jann Horn points out that our TLB flushing was subtly wrong for the +mremap() case. What makes mremap() special is that we don't follow the +usual "add page to list of pages to be freed, then flush tlb, and then +free pages". No, mremap() obviously just _moves_ the page from one page +table location to another. + +That matters, because mremap() thus doesn't directly control the +lifetime of the moved page with a freelist: instead, the lifetime of the +page is controlled by the page table locking, that serializes access to +the entry. + +As a result, we need to flush the TLB not just before releasing the lock +for the source location (to avoid any concurrent accesses to the entry), +but also before we release the destination page table lock (to avoid the +TLB being flushed after somebody else has already done something to that +page). + +This also makes the whole "need_flush" logic unnecessary, since we now +always end up flushing the TLB for every valid entry. + +Reported-and-tested-by: Jann Horn +Acked-by: Will Deacon +Tested-by: Ingo Molnar +Acked-by: Peter Zijlstra (Intel) +Signed-off-by: Linus Torvalds +Signed-off-by: Greg Kroah-Hartman +--- + include/linux/huge_mm.h | 2 +- + mm/huge_memory.c | 10 ++++------ + mm/mremap.c | 30 +++++++++++++----------------- + 3 files changed, 18 insertions(+), 24 deletions(-) + +diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h +index 99c19b06d9a4..fdcb45999b26 100644 +--- a/include/linux/huge_mm.h ++++ b/include/linux/huge_mm.h +@@ -43,7 +43,7 @@ extern int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, + unsigned char *vec); + extern bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, + unsigned long new_addr, unsigned long old_end, +- pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush); ++ pmd_t *old_pmd, pmd_t *new_pmd); + extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, + unsigned long addr, pgprot_t newprot, + int prot_numa); +diff --git a/mm/huge_memory.c b/mm/huge_memory.c +index 58269f8ba7c4..deed97fba979 100644 +--- a/mm/huge_memory.c ++++ b/mm/huge_memory.c +@@ -1780,7 +1780,7 @@ static pmd_t move_soft_dirty_pmd(pmd_t pmd) + + bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, + unsigned long new_addr, unsigned long old_end, +- pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush) ++ pmd_t *old_pmd, pmd_t *new_pmd) + { + spinlock_t *old_ptl, *new_ptl; + pmd_t pmd; +@@ -1811,7 +1811,7 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, + if (new_ptl != old_ptl) + spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); + pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd); +- if (pmd_present(pmd) && pmd_dirty(pmd)) ++ if (pmd_present(pmd)) + force_flush = true; + VM_BUG_ON(!pmd_none(*new_pmd)); + +@@ -1822,12 +1822,10 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, + } + pmd = move_soft_dirty_pmd(pmd); + set_pmd_at(mm, new_addr, new_pmd, pmd); +- if (new_ptl != old_ptl) +- spin_unlock(new_ptl); + if (force_flush) + flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE); +- else +- *need_flush = true; ++ if (new_ptl != old_ptl) ++ spin_unlock(new_ptl); + spin_unlock(old_ptl); + return true; + } +diff --git a/mm/mremap.c b/mm/mremap.c +index 5c2e18505f75..a9617e72e6b7 100644 +--- a/mm/mremap.c ++++ b/mm/mremap.c +@@ -115,7 +115,7 @@ static pte_t move_soft_dirty_pte(pte_t pte) + static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, + unsigned long old_addr, unsigned long old_end, + struct vm_area_struct *new_vma, pmd_t *new_pmd, +- unsigned long new_addr, bool need_rmap_locks, bool *need_flush) ++ unsigned long new_addr, bool need_rmap_locks) + { + struct mm_struct *mm = vma->vm_mm; + pte_t *old_pte, *new_pte, pte; +@@ -163,15 +163,17 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, + + pte = ptep_get_and_clear(mm, old_addr, old_pte); + /* +- * If we are remapping a dirty PTE, make sure ++ * If we are remapping a valid PTE, make sure + * to flush TLB before we drop the PTL for the +- * old PTE or we may race with page_mkclean(). ++ * PTE. + * +- * This check has to be done after we removed the +- * old PTE from page tables or another thread may +- * dirty it after the check and before the removal. ++ * NOTE! Both old and new PTL matter: the old one ++ * for racing with page_mkclean(), the new one to ++ * make sure the physical page stays valid until ++ * the TLB entry for the old mapping has been ++ * flushed. + */ +- if (pte_present(pte) && pte_dirty(pte)) ++ if (pte_present(pte)) + force_flush = true; + pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr); + pte = move_soft_dirty_pte(pte); +@@ -179,13 +181,11 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, + } + + arch_leave_lazy_mmu_mode(); ++ if (force_flush) ++ flush_tlb_range(vma, old_end - len, old_end); + if (new_ptl != old_ptl) + spin_unlock(new_ptl); + pte_unmap(new_pte - 1); +- if (force_flush) +- flush_tlb_range(vma, old_end - len, old_end); +- else +- *need_flush = true; + pte_unmap_unlock(old_pte - 1, old_ptl); + if (need_rmap_locks) + drop_rmap_locks(vma); +@@ -198,7 +198,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma, + { + unsigned long extent, next, old_end; + pmd_t *old_pmd, *new_pmd; +- bool need_flush = false; + unsigned long mmun_start; /* For mmu_notifiers */ + unsigned long mmun_end; /* For mmu_notifiers */ + +@@ -229,8 +228,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, + if (need_rmap_locks) + take_rmap_locks(vma); + moved = move_huge_pmd(vma, old_addr, new_addr, +- old_end, old_pmd, new_pmd, +- &need_flush); ++ old_end, old_pmd, new_pmd); + if (need_rmap_locks) + drop_rmap_locks(vma); + if (moved) +@@ -246,10 +244,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma, + if (extent > next - new_addr) + extent = next - new_addr; + move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, +- new_pmd, new_addr, need_rmap_locks, &need_flush); ++ new_pmd, new_addr, need_rmap_locks); + } +- if (need_flush) +- flush_tlb_range(vma, old_end-len, old_addr); + + mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); + +-- +2.11.0 + diff --git a/debian/patches/series b/debian/patches/series index 55b9f8e2c..13e83e91c 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -145,6 +145,7 @@ features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch # Security fixes debian/i386-686-pae-pci-set-pci-nobios-by-default.patch bugfix/all/Revert-net-increase-fragment-memory-usage-limits.patch +bugfix/all/mremap-properly-flush-TLB-before-releasing-the-page.patch # Fix exported symbol versions bugfix/all/module-disable-matching-missing-version-crc.patch