From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH v2 net] net: filter: x86: fix JIT address randomization Date: Tue, 13 May 2014 15:05:55 -0700 Message-ID: <1400018755-3049-1-git-send-email-ast@plumgrid.com> Cc: Eric Dumazet , "H. Peter Anvin" , Daniel Borkmann , Heiko Carstens , netdev@vger.kernel.org To: "David S. Miller" Return-path: Received: from mail-pa0-f54.google.com ([209.85.220.54]:62735 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932256AbaEMWGB (ORCPT ); Tue, 13 May 2014 18:06:01 -0400 Received: by mail-pa0-f54.google.com with SMTP id bj1so772325pad.41 for ; Tue, 13 May 2014 15:06:00 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: 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: [] change_page_attr_set_clr+0x135/0x460 [] ? _raw_spin_unlock_irq+0x30/0x50 [] set_memory_rw+0x2f/0x40 [] bpf_jit_free_deferred+0x2d/0x60 [] process_one_work+0x1d8/0x6a0 [] ? process_one_work+0x178/0x6a0 [] 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: 314beb9bcabfd ("x86: bpf_jit_comp: secure bpf jit against spraying attacks") Signed-off-by: Alexei Starovoitov --- arch/x86/net/bpf_jit_comp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index dc01773..6d5663a 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -171,7 +171,7 @@ static struct bpf_binary_header *bpf_alloc_binary(unsigned int proglen, memset(header, 0xcc, sz); /* fill whole space with int3 instructions */ header->pages = sz / PAGE_SIZE; - hole = sz - (proglen + sizeof(*header)); + hole = min(sz - (proglen + sizeof(*header)), PAGE_SIZE - sizeof(*header)); /* insert a random number of int3 instructions before BPF code */ *image_ptr = &header->image[prandom_u32() % hole]; -- 1.7.9.5