Re: [PATCH] livepatch: x86: bugfix about kASLR

From: zhouchengming
Date: Wed Nov 04 2015 - 05:06:12 EST

On 2015/11/4 17:44, Jiri Kosina wrote:
On Wed, 4 Nov 2015, Zhou Chengming wrote:

When enable KASLR, func->old_addr will be set to zero
and livepatch will find the right old address.
But for reloc, livepatch just verify it using reloc->val
(old addr from user), so verify failed and report
"kernel mismatch" error.

Reported-by: Cyril B.<cbay@xxxxxxxxxxxxxx>
Signed-off-by: Zhou Chengming<zhouchengming1@xxxxxxxxxx>
kernel/livepatch/core.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 53196e2..c8885c6 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -311,7 +311,12 @@ static int klp_write_object_relocations(struct module *pmod,
return -EINVAL;

for (reloc = obj->relocs; reloc->name; reloc++) {
- if (!klp_is_module(obj)) {
CONFIG_RANDOMIZE_BASE being enabled by itself doesn't directly imply that
kASLR has been actually really enabled during runtime. You need
to check kaslr_enabled() as well.


+ /* KASLR is enabled, disregard old_addr from user */
+ reloc->val = 0;
Is there a reason why to discard it completely? Adding kaslr_offset()
should give us the correct address, right?


Yes, it's definitely better.


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