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    Subject[PATCH 3/3] /dev/mem: Do not map unaccepted memory
    Date
    Support for unaccepted memory was added recently, refer commit
    dcdfdd40fa82 ("mm: Add support for unaccepted memory"), whereby
    a virtual machine may need to accept memory before it can be used.

    Do not map unaccepted memory because it can cause the guest to fail.

    For /dev/mem, this means a read of unaccepted memory will return zeros,
    a write to unaccepted memory will be ignored, but an mmap of unaccepted
    memory will return an error.

    Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory")
    Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
    ---
    drivers/char/mem.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    diff --git a/drivers/char/mem.c b/drivers/char/mem.c
    index 1052b0f2d4cf..1a7c5728783c 100644
    --- a/drivers/char/mem.c
    +++ b/drivers/char/mem.c
    @@ -147,7 +147,8 @@ static ssize_t read_mem(struct file *file, char __user *buf,
    goto failed;

    err = -EFAULT;
    - if (allowed == 2) {
    + if (allowed == 2 ||
    + range_contains_unaccepted_memory(p, p + sz)) {
    /* Show zeros for restricted memory. */
    remaining = clear_user(buf, sz);
    } else {
    @@ -226,7 +227,8 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
    return -EPERM;

    /* Skip actual writing when a page is marked as restricted. */
    - if (allowed == 1) {
    + if (allowed == 1 &&
    + !range_contains_unaccepted_memory(p, p + sz)) {
    /*
    * On ia64 if a page has been mapped somewhere as
    * uncached, then it must also be accessed uncached
    @@ -378,6 +380,9 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
    &vma->vm_page_prot))
    return -EINVAL;

    + if (range_contains_unaccepted_memory(offset, offset + size))
    + return -EINVAL;
    +
    vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
    size,
    vma->vm_page_prot);
    --
    2.34.1
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