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Re: [Xen-devel] [PATCH v6 07/12] livepatch: Add per-function applied/reverted state tracking marker


  • To: "Wieczorkiewicz, Pawel" <wipawel@xxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 6 Jan 2020 12:25:46 +0000
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, "Pohlack, Martin" <mpohlack@xxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, "Manthey, Norbert" <nmanthey@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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On 06/01/2020 12:22, Wieczorkiewicz, Pawel wrote:


On 5. Jan 2020, at 12:36, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

On 26/11/2019 10:07, Pawel Wieczorkiewicz wrote:
@@ -1274,6 +1297,9 @@ static void livepatch_do_action(void)
        else
<snip>
        break;
@@ -1309,6 +1338,9 @@ static void livepatch_do_action(void)
            else
                other->rc = revert_payload(other);

+            if ( !was_action_consistent(other, rc ? LIVEPATCH_FUNC_APPLIED : LIVEPATCH_FUNC_NOT_APPLIED) )
+                panic("livepatch: partially reverted payload '%s'!\n", other->name);
+
            if ( other->rc == 0 )
                revert_payload_tail(other);

Coverity highlights that this contains dead code.

The LIVEPATCH_ACTION_REPLACE case, unlike all others, uses other->rc,
which means the rc ? : check will always pass LIVEPATCH_FUNC_APPLIED
into was_action_consistent(), due to the rc = 0 at the head of the case
block.


Yes, this has to be other->rc instead of rc. Thanks!

If this were the only problem, switching rc to other->rc might be ok,
but there look to be other confusions in the surrounding code.  Would
you mind looking over the whole block of code for correct error handling?


What are the confusions in the code? Could you be more specific and point me to them?

I have just checked the LIVEPATCH_ACTION_REPLACE case block again.
It looks correct to me. That is, it preserves the original logic of error handling there.
I just added the extensions. But, the flow for rc and other->rc should be the same
and correct (modulo the was_action_consistent() bug).

So long as you've double checked and you think the rest of the logic is fine, then ok.  It was the further mixed use of rc vs other->rc which I was concerned about.

~Andrew

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