• David Howells's avatar
    NOMMU: Fix MAP_PRIVATE mmap() of objects where the data can be mapped directly · 645d83c5
    David Howells authored
    Fix MAP_PRIVATE mmap() of files and devices where the data in the backing store
    might be mapped directly.  Use the BDI_CAP_MAP_DIRECT capability flag to govern
    whether or not we should be trying to map a file directly.  This can be used to
    determine whether or not a region has been filled in at the point where we call
    do_mmap_shared() or do_mmap_private().
    
    The BDI_CAP_MAP_DIRECT capability flag is cleared by validate_mmap_request() if
    there's any reason we can't use it.  It's also cleared in do_mmap_pgoff() if
    f_op->get_unmapped_area() fails.
    
    Without this fix, attempting to run a program from a RomFS image on a
    non-mappable MTD partition results in a BUG as the kernel attempts XIP, and
    this can be caught in gdb:
    
    Program received signal SIGABRT, Aborted.
    0xc005dce8 in add_nommu_region (region=<value optimized out>) at mm/nommu.c:547
    (gdb) bt
    #0  0xc005dce8 in add_nommu_region (region=<value optimized out>) at mm/nommu.c:547
    #1  0xc005f168 in do_mmap_pgoff (file=0xc31a6620, addr=<value optimized out>, len=3808, prot=3, flags=6146, pgoff=0) at mm/nommu.c:1373
    #2  0xc00a96b8 in elf_fdpic_map_file (params=0xc33fbbec, file=0xc31a6620, mm=0xc31bef60, what=0xc0213144 "executable") at mm.h:1145
    #3  0xc00aa8b4 in load_elf_fdpic_binary (bprm=0xc316cb00, regs=<value optimized out>) at fs/binfmt_elf_fdpic.c:343
    #4  0xc006b588 in search_binary_handler (bprm=0x6, regs=0xc33fbce0) at fs/exec.c:1234
    #5  0xc006c648 in do_execve (filename=<value optimized out>, argv=0xc3ad14cc, envp=0xc3ad1460, regs=0xc33fbce0) at fs/exec.c:1356
    #6  0xc0008cf0 in sys_execve (name=<value optimized out>, argv=0xc3ad14cc, envp=0xc3ad1460) at arch/frv/kernel/process.c:263
    #7  0xc00075dc in __syscall_call () at arch/frv/kernel/entry.S:897
    
    Note that this fix does the following commit differently:
    
    	commit a190887b
    	Author: David Howells <dhowells@redhat.com>
    	Date:   Sat Sep 5 11:17:07 2009 -0700
    	nommu: fix error handling in do_mmap_pgoff()
    Reported-by: default avatarGraff Yang <graff.yang@gmail.com>
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Acked-by: default avatarPekka Enberg <penberg@cs.helsinki.fi>
    Cc: Paul Mundt <lethal@linux-sh.org>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Greg Ungerer <gerg@snapgear.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    645d83c5
nommu.c 45.7 KB