mm: fix double page fault on arm64 if PTE_AF is cleared
[ Upstream commit 83d116c530
]
When we tested pmdk unit test [1] vmmalloc_fork TEST3 on arm64 guest, there
will be a double page fault in __copy_from_user_inatomic of cow_user_page.
To reproduce the bug, the cmd is as follows after you deployed everything:
make -C src/test/vmmalloc_fork/ TEST_TIME=60m check
Below call trace is from arm64 do_page_fault for debugging purpose:
[ 110.016195] Call trace:
[ 110.016826] do_page_fault+0x5a4/0x690
[ 110.017812] do_mem_abort+0x50/0xb0
[ 110.018726] el1_da+0x20/0xc4
[ 110.019492] __arch_copy_from_user+0x180/0x280
[ 110.020646] do_wp_page+0xb0/0x860
[ 110.021517] __handle_mm_fault+0x994/0x1338
[ 110.022606] handle_mm_fault+0xe8/0x180
[ 110.023584] do_page_fault+0x240/0x690
[ 110.024535] do_mem_abort+0x50/0xb0
[ 110.025423] el0_da+0x20/0x24
The pte info before __copy_from_user_inatomic is (PTE_AF is cleared):
[ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003,
pmd=000000023d4b3003, pte=360000298607bd3
As told by Catalin: "On arm64 without hardware Access Flag, copying from
user will fail because the pte is old and cannot be marked young. So we
always end up with zeroed page after fork() + CoW for pfn mappings. we
don't always have a hardware-managed access flag on arm64."
This patch fixes it by calling pte_mkyoung. Also, the parameter is
changed because vmf should be passed to cow_user_page()
Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error
in case there can be some obscure use-case (by Kirill).
[1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
Signed-off-by: Jia He <justin.he@arm.com>
Reported-by: Yibo Cai <Yibo.Cai@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
5.4-rM2-2.2.x-imx-squashed
parent
bdb830d101
commit
2c25b95111
104
mm/memory.c
104
mm/memory.c
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@ -118,6 +118,18 @@ int randomize_va_space __read_mostly =
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2;
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2;
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#endif
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#endif
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#ifndef arch_faults_on_old_pte
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static inline bool arch_faults_on_old_pte(void)
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{
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/*
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* Those arches which don't have hw access flag feature need to
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* implement their own helper. By default, "true" means pagefault
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* will be hit on old pte.
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*/
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return true;
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}
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#endif
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static int __init disable_randmaps(char *s)
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static int __init disable_randmaps(char *s)
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{
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{
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randomize_va_space = 0;
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randomize_va_space = 0;
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@ -2145,32 +2157,82 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
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return same;
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return same;
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}
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}
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static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
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static inline bool cow_user_page(struct page *dst, struct page *src,
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struct vm_fault *vmf)
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{
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{
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bool ret;
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void *kaddr;
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void __user *uaddr;
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bool force_mkyoung;
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struct vm_area_struct *vma = vmf->vma;
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struct mm_struct *mm = vma->vm_mm;
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unsigned long addr = vmf->address;
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debug_dma_assert_idle(src);
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debug_dma_assert_idle(src);
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if (likely(src)) {
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copy_user_highpage(dst, src, addr, vma);
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return true;
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}
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/*
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/*
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* If the source page was a PFN mapping, we don't have
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* If the source page was a PFN mapping, we don't have
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* a "struct page" for it. We do a best-effort copy by
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* a "struct page" for it. We do a best-effort copy by
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* just copying from the original user address. If that
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* just copying from the original user address. If that
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* fails, we just zero-fill it. Live with it.
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* fails, we just zero-fill it. Live with it.
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*/
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*/
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if (unlikely(!src)) {
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kaddr = kmap_atomic(dst);
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void *kaddr = kmap_atomic(dst);
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uaddr = (void __user *)(addr & PAGE_MASK);
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void __user *uaddr = (void __user *)(va & PAGE_MASK);
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/*
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* On architectures with software "accessed" bits, we would
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* take a double page fault, so mark it accessed here.
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*/
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force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte);
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if (force_mkyoung) {
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pte_t entry;
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vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
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if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
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/*
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* Other thread has already handled the fault
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* and we don't need to do anything. If it's
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* not the case, the fault will be triggered
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* again on the same address.
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*/
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ret = false;
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goto pte_unlock;
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}
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entry = pte_mkyoung(vmf->orig_pte);
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if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
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update_mmu_cache(vma, addr, vmf->pte);
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}
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/*
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* This really shouldn't fail, because the page is there
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* in the page tables. But it might just be unreadable,
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* in which case we just give up and fill the result with
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* zeroes.
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*/
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if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
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/*
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/*
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* This really shouldn't fail, because the page is there
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* Give a warn in case there can be some obscure
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* in the page tables. But it might just be unreadable,
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* use-case
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* in which case we just give up and fill the result with
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* zeroes.
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*/
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*/
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if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
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WARN_ON_ONCE(1);
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clear_page(kaddr);
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clear_page(kaddr);
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kunmap_atomic(kaddr);
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}
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flush_dcache_page(dst);
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} else
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ret = true;
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copy_user_highpage(dst, src, va, vma);
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pte_unlock:
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if (force_mkyoung)
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pte_unmap_unlock(vmf->pte, vmf->ptl);
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kunmap_atomic(kaddr);
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flush_dcache_page(dst);
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return ret;
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}
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}
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static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
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static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
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@ -2342,7 +2404,19 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
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vmf->address);
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vmf->address);
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if (!new_page)
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if (!new_page)
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goto oom;
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goto oom;
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cow_user_page(new_page, old_page, vmf->address, vma);
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if (!cow_user_page(new_page, old_page, vmf)) {
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/*
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* COW failed, if the fault was solved by other,
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* it's fine. If not, userspace would re-fault on
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* the same address and we will handle the fault
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* from the second attempt.
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*/
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put_page(new_page);
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if (old_page)
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put_page(old_page);
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return 0;
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}
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}
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}
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if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
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if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
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