• Heiko Carstens's avatar
    net: filter: s390: fix JIT address randomization · e84d2f8d
    Heiko Carstens authored
    This is the s390 variant of Alexei's JIT bug fix.
    (patch description below stolen from Alexei's patch)
    bpf_alloc_binary() adds 128 bytes of room to JITed program image
    and rounds it up to the nearest page size. If image size is close
    to page size (like 4000), it is rounded to two pages:
    round_up(4000 + 4 + 128) == 8192
    then 'hole' is computed as 8192 - (4000 + 4) = 4188
    If prandom_u32() % hole selects a number >= PAGE_SIZE - sizeof(*header)
    then kernel will crash during bpf_jit_free():
    kernel BUG at arch/x86/mm/pageattr.c:887!
    Call Trace:
     [<ffffffff81037285>] change_page_attr_set_clr+0x135/0x460
     [<ffffffff81694cc0>] ? _raw_spin_unlock_irq+0x30/0x50
     [<ffffffff810378ff>] set_memory_rw+0x2f/0x40
     [<ffffffffa01a0d8d>] bpf_jit_free_deferred+0x2d/0x60
     [<ffffffff8106bf98>] process_one_work+0x1d8/0x6a0
     [<ffffffff8106bf38>] ? process_one_work+0x178/0x6a0
     [<ffffffff8106c90c>] worker_thread+0x11c/0x370
    since bpf_jit_free() does:
      unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
      struct bpf_binary_header *header = (void *)addr;
    to compute start address of 'bpf_binary_header'
    and header->pages will pass junk to:
      set_memory_rw(addr, header->pages);
    Fix it by making sure that &header->image[prandom_u32() % hole] and &header
    are in the same page.
    Fixes: aa2d2c73
     ("s390/bpf,jit: address randomize and write protect jit code")
    Reported-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
    Cc: <stable@vger.kernel.org> # v3.11+
    Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>