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Re: [PATCH 1/2] livepatch: do not ignore sections with 0 size
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Thu, 7 Apr 2022 16:16:12 +0000
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- Thread-topic: [PATCH 1/2] livepatch: do not ignore sections with 0 size
> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Sent: Thursday, March 17, 2022 11:08 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>; Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Subject: [PATCH 1/2] livepatch: do not ignore sections with 0 size
>
> A side effect of ignoring such sections is that symbols belonging to
> them won't be resolved, and that could make relocations belonging to
> other sections that reference those symbols fail.
>
> For example it's likely to have an empty .altinstr_replacement with
> symbols pointing to it, and marking the section as ignored will
> prevent the symbols from being resolved, which in turn will cause any
> relocations against them to fail.
>
> In order to solve this do not ignore sections with 0 size, only ignore
> sections that don't have the SHF_ALLOC flag set.
>
> Special case such empty sections in move_payload so they are not taken
> into account in order to decide whether a livepatch can be safely
> re-applied after a revert.
>
> Fixes: 98b728a7b2 ('livepatch: Disallow applying after an revert')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
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