lkml.org 
[lkml]   [2018]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Subject[PATCH 2/5] mm: allow non-direct-map arguments to free_reserved_area()
    From
    Date

    From: Dave Hansen <dave.hansen@linux.intel.com>

    free_reserved_area() takes pointers as arguments to show which
    addresses should be freed. However, it does this in a
    somewhat ambiguous way. If it gets a kernel direct map address,
    it always works. However, if it gets an address that is
    part of the kernel image alias mapping, it can fail.

    It fails if all of the following happen:
    * The specified address is part of the kernel image alias
    * Poisoning is requested (forcing a memset())
    * The address is in a read-only portion of the kernel image

    The memset() fails on the read-only mapping, of course.
    free_reserved_area() *is* called both on the direct map and
    on kernel image alias addresses. We've just lucked out thus
    far that the kernel image alias areas it gets used on are
    read-write. I'm fairly sure this has been just a happy
    accident.

    It is quite easy to make free_reserved_area() work for all
    cases: just convert the address to a direct map address before
    doing the memset(), and do this unconditionally. There is
    little chance of a regression here because we previously
    did a virt_to_page() on the address for the memset, so we
    know these are no highmem pages for which virt_to_page()
    would fail.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Kees Cook <keescook@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Andi Kleen <ak@linux.intel.com>
    ---

    b/mm/page_alloc.c | 16 ++++++++++++++--
    1 file changed, 14 insertions(+), 2 deletions(-)

    diff -puN mm/page_alloc.c~x86-mm-init-handle-non-linear-map-ranges-free_init_pages mm/page_alloc.c
    --- a/mm/page_alloc.c~x86-mm-init-handle-non-linear-map-ranges-free_init_pages 2018-07-30 09:53:13.259915693 -0700
    +++ b/mm/page_alloc.c 2018-07-30 09:53:13.264915693 -0700
    @@ -6934,9 +6934,21 @@ unsigned long free_reserved_area(void *s
    start = (void *)PAGE_ALIGN((unsigned long)start);
    end = (void *)((unsigned long)end & PAGE_MASK);
    for (pos = start; pos < end; pos += PAGE_SIZE, pages++) {
    + struct page *page = virt_to_page(pos);
    + void *direct_map_addr;
    +
    + /*
    + * 'direct_map_addr' might be different from 'pos'
    + * because some architectures' virt_to_page()
    + * work with aliases. Getting the direct map
    + * address ensures that we get a _writeable_
    + * alias for the memset().
    + */
    + direct_map_addr = page_address(page);
    if ((unsigned int)poison <= 0xFF)
    - memset(pos, poison, PAGE_SIZE);
    - free_reserved_page(virt_to_page(pos));
    + memset(direct_map_addr, poison, PAGE_SIZE);
    +
    + free_reserved_page(page);
    }

    if (pages && s)
    _
    \
     
     \ /
      Last update: 2018-08-01 20:02    [W:3.175 / U:0.236 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site