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    Subject[PATCH v4 08/10] vfs, fdtable: prevent bounds-check bypass via speculative execution
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    'fd' is a user controlled value that is used as a data dependency to
    read from the 'fdt->fd' array. In order to avoid potential leaks of
    kernel memory values, block speculative execution of the instruction
    stream that could issue reads based on an invalid 'file *' returned from
    __fcheck_files.

    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Co-developed-by: Elena Reshetova <elena.reshetova@intel.com>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    ---
    include/linux/fdtable.h | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
    index 1c65817673db..9731f1a255db 100644
    --- a/include/linux/fdtable.h
    +++ b/include/linux/fdtable.h
    @@ -10,6 +10,7 @@
    #include <linux/compiler.h>
    #include <linux/spinlock.h>
    #include <linux/rcupdate.h>
    +#include <linux/nospec.h>
    #include <linux/types.h>
    #include <linux/init.h>
    #include <linux/fs.h>
    @@ -81,9 +82,11 @@ struct dentry;
    static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd)
    {
    struct fdtable *fdt = rcu_dereference_raw(files->fdt);
    + struct file __rcu **fdp;

    - if (fd < fdt->max_fds)
    - return rcu_dereference_raw(fdt->fd[fd]);
    + fdp = array_ptr(fdt->fd, fd, fdt->max_fds);
    + if (fdp)
    + return rcu_dereference_raw(*fdp);
    return NULL;
    }

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