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Date: Fri, 2 Jun 2017 11:20:05 -0400
From: riel@...hat.com
To: linux-kernel@...r.kernel.org
Cc: kernel-hardening@...ts.openwall.com, akpm@...ux-foundation.org,
mingo@...nel.org, oleg@...hat.com, lwoodman@...hat.com, mhocko@...e.de,
danielmicay@...il.com, will.deacon@....com, benh@...nel.crashing.org
Subject: [PATCH 1/6] binfmt_elf: document load_bias a little bit
From: Rik van Riel <riel@...hat.com>
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 <riel@...hat.com>
---
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
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