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Subject[PATCH v2 10/26] userfaultfd: wp: add UFFDIO_COPY_MODE_WP
Date
From: Andrea Arcangeli <aarcange@redhat.com>

This allows UFFDIO_COPY to map pages wrprotected.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/userfaultfd.c | 5 +++--
include/linux/userfaultfd_k.h | 2 +-
include/uapi/linux/userfaultfd.h | 11 +++++-----
mm/userfaultfd.c | 36 ++++++++++++++++++++++----------
4 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index b397bc3b954d..3092885c9d2c 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1683,11 +1683,12 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
ret = -EINVAL;
if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
goto out;
- if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
+ if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
goto out;
if (mmget_not_zero(ctx->mm)) {
ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
- uffdio_copy.len, &ctx->mmap_changing);
+ uffdio_copy.len, &ctx->mmap_changing,
+ uffdio_copy.mode);
mmput(ctx->mm);
} else {
return -ESRCH;
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index c6590c58ce28..765ce884cec0 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -34,7 +34,7 @@ extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason);

extern ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
unsigned long src_start, unsigned long len,
- bool *mmap_changing);
+ bool *mmap_changing, __u64 mode);
extern ssize_t mfill_zeropage(struct mm_struct *dst_mm,
unsigned long dst_start,
unsigned long len,
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 48f1a7c2f1f0..297cb044c03f 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -203,13 +203,14 @@ struct uffdio_copy {
__u64 dst;
__u64 src;
__u64 len;
+#define UFFDIO_COPY_MODE_DONTWAKE ((__u64)1<<0)
/*
- * There will be a wrprotection flag later that allows to map
- * pages wrprotected on the fly. And such a flag will be
- * available if the wrprotection ioctl are implemented for the
- * range according to the uffdio_register.ioctls.
+ * UFFDIO_COPY_MODE_WP will map the page wrprotected on the
+ * fly. UFFDIO_COPY_MODE_WP is available only if the
+ * wrprotection ioctl are implemented for the range according
+ * to the uffdio_register.ioctls.
*/
-#define UFFDIO_COPY_MODE_DONTWAKE ((__u64)1<<0)
+#define UFFDIO_COPY_MODE_WP ((__u64)1<<1)
__u64 mode;

/*
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index d59b5a73dfb3..73a208c5c1e7 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -25,7 +25,8 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
struct vm_area_struct *dst_vma,
unsigned long dst_addr,
unsigned long src_addr,
- struct page **pagep)
+ struct page **pagep,
+ bool wp_copy)
{
struct mem_cgroup *memcg;
pte_t _dst_pte, *dst_pte;
@@ -71,9 +72,9 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
goto out_release;

- _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
- if (dst_vma->vm_flags & VM_WRITE)
- _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
+ _dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
+ if (dst_vma->vm_flags & VM_WRITE && !wp_copy)
+ _dst_pte = pte_mkwrite(_dst_pte);

dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
if (dst_vma->vm_file) {
@@ -399,7 +400,8 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
unsigned long dst_addr,
unsigned long src_addr,
struct page **page,
- bool zeropage)
+ bool zeropage,
+ bool wp_copy)
{
ssize_t err;

@@ -416,11 +418,13 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
if (!(dst_vma->vm_flags & VM_SHARED)) {
if (!zeropage)
err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
- dst_addr, src_addr, page);
+ dst_addr, src_addr, page,
+ wp_copy);
else
err = mfill_zeropage_pte(dst_mm, dst_pmd,
dst_vma, dst_addr);
} else {
+ VM_WARN_ON(wp_copy); /* WP only available for anon */
if (!zeropage)
err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
dst_vma, dst_addr,
@@ -438,7 +442,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
unsigned long src_start,
unsigned long len,
bool zeropage,
- bool *mmap_changing)
+ bool *mmap_changing,
+ __u64 mode)
{
struct vm_area_struct *dst_vma;
ssize_t err;
@@ -446,6 +451,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
unsigned long src_addr, dst_addr;
long copied;
struct page *page;
+ bool wp_copy;

/*
* Sanitize the command parameters:
@@ -502,6 +508,14 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
dst_vma->vm_flags & VM_SHARED))
goto out_unlock;

+ /*
+ * validate 'mode' now that we know the dst_vma: don't allow
+ * a wrprotect copy if the userfaultfd didn't register as WP.
+ */
+ wp_copy = mode & UFFDIO_COPY_MODE_WP;
+ if (wp_copy && !(dst_vma->vm_flags & VM_UFFD_WP))
+ goto out_unlock;
+
/*
* If this is a HUGETLB vma, pass off to appropriate routine
*/
@@ -557,7 +571,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
BUG_ON(pmd_trans_huge(*dst_pmd));

err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
- src_addr, &page, zeropage);
+ src_addr, &page, zeropage, wp_copy);
cond_resched();

if (unlikely(err == -ENOENT)) {
@@ -604,14 +618,14 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,

ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
unsigned long src_start, unsigned long len,
- bool *mmap_changing)
+ bool *mmap_changing, __u64 mode)
{
return __mcopy_atomic(dst_mm, dst_start, src_start, len, false,
- mmap_changing);
+ mmap_changing, mode);
}

ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
unsigned long len, bool *mmap_changing)
{
- return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing);
+ return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing, 0);
}
--
2.17.1
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