From mboxrd@z Thu Jan 1 00:00:00 1970 From: riel@redhat.com Date: Fri, 2 Jun 2017 11:20:05 -0400 Message-Id: <20170602152010.2064-2-riel@redhat.com> In-Reply-To: <20170602152010.2064-1-riel@redhat.com> References: <20170602152010.2064-1-riel@redhat.com> Subject: [kernel-hardening] [PATCH 1/6] binfmt_elf: document load_bias a little bit To: linux-kernel@vger.kernel.org Cc: kernel-hardening@lists.openwall.com, akpm@linux-foundation.org, mingo@kernel.org, oleg@redhat.com, lwoodman@redhat.com, mhocko@suse.de, danielmicay@gmail.com, will.deacon@arm.com, benh@kernel.crashing.org List-ID: From: Rik van Riel After me and another unnamed developer got confused by the subtraction of vaddr in this branch of the code, followed by adding vaddr back in a little bit later, for the third time, maybe it is time to document this quirky bit of code. Signed-off-by: Rik van Riel --- fs/binfmt_elf.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 5075fd5c62c8..8c3f4dbc7603 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -930,10 +930,16 @@ static int load_elf_binary(struct linux_binprm *bprm) if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) { elf_flags |= MAP_FIXED; } else if (loc->elf_ex.e_type == ET_DYN) { - /* Try and get dynamic programs out of the way of the + /* + * Try and get dynamic programs out of the way of the * default mmap base, as well as whatever program they * might try to exec. This is because the brk will - * follow the loader, and is not movable. */ + * follow the loader, and is not movable. + * + * The load_bias is the difference between the address + * in the elf header and the address where the binary + * is mmapped. + */ load_bias = ELF_ET_DYN_BASE - vaddr; if (current->flags & PF_RANDOMIZE) load_bias += arch_mmap_rnd(); -- 2.9.3