On 06/30/2017 11:49 AM, Josh Poimboeuf wrote:
On Wed, Jun 28, 2017 at 04:36:13PM -0500, Josh Poimboeuf wrote:
On Wed, Jun 28, 2017 at 04:34:18PM -0500, Josh Poimboeuf wrote:
On Wed, Jun 28, 2017 at 04:25:19PM -0500, Josh Poimboeuf wrote:
On Wed, Jun 28, 2017 at 02:02:09PM -0400, Jason Baron wrote:
Hi,
If I have kernel source S, apply a kpatch module A, but then want to
'revert' parts of A, by applying a cumulative patch B, such that some
functions are no longer different from source kernel S, how do I do that?
It seems like there are a few options:
1) remove or disable module A, then load module B. This leaves an
un-patched window and rmmod isn't possible without reliable backtrace.
I'm also not sure this works with the kpatch 'stacking'.
2) modify patch B such that any functions that are initially unchanged
from S, are in fact modified but modified in an acceptable way.
3) maybe the kernel can understand that are not added to or modified by
a cumulative patch should be reverted back to their original state?
#3 seems to me to be the cleanest...but maybe I'm missing something...
Hi Jason,
We don't have a mechanism for reverting patches, so #2 will probably be
your best bet.
Sorry, that was both poorly worded and incorrect, let me try again :-)
I meant to say we don't have a mechanism for atomically replacing the
entire contents of patch A with patch B.
But I was mistaken. Technically we do have a "replace" mechanism. It
was deprecated, see https://github.com/dynup/kpatch/issues/456 for more
details. But it should work in theory if you load the patch module
manually with insmod and the 'replace=1' argument. We had some issues
with it though, so #2 might be a safer bet.
And I should note that the replace only works with kpatch.ko, not with
livepatch. We may add replace support to livepatch eventually.
FYI, I'm proposing a new KPATCH_REVERT_FUNCTION macro which makes this a
little easier, so you can use the macro instead of making a trivial
change to the function:
https://github.com/dynup/kpatch/pull/715
I have to explicitly mark functions as revert, right?
I'm wondering though if the function is inlined then I have to go and
mark all the places where it was inlined as KPATCH_REVERT_FUNCTION()?
And further there may be other changes in some of those functions and
not others.
So it seems like it would be nice to calculate this based on the
previous set of loaded modules, or from the state of currently patched
kernel.
Thanks,
-Jason
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