Re: [PATCH 0/2] livepatch: fix handling of (some) relocations

["Doebel, Bjoern" <doebel@xxxxxxxxx>]

On 17.03.22, 12:10, "Xen-devel on behalf of Roger Pau Monne" 
<xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx on behalf of roger.pau@xxxxxxxxxx> 
wrote:


    Hello,

    Relocations that reference symbols that belong to sections with a size
    of 0 are not properly resolved, as the address of those symbols won't be
    resolved in the first place.

    Fix this by not ignoring sections with a size of 0, while still properly
    handling the detection of whether a livepatch can be reapplied after
    being reverted (patch 1).

    Also detect whether any relocations reference unresolved symbols and
    error out in that case, as those relocations cannot be resolved (patch
    2).

    I wonder whether it's possible to have unresolved symbols if we only
    ignore non SHF_ALLOC sections, so we could maybe error out earlier if we
    found a symbols that belongs to a non SHF_ALLOC section in
    livepatch_elf_resolve_symbols.  The current approach is more conservative
    as we would only report an error if we have unresolved symbols that are
    referenced in relocations.

    Thanks, Roger.

    Roger Pau Monne (2):
      livepatch: do not ignore sections with 0 size
      livepatch: avoid relocations referencing ignored section symbols

     xen/arch/arm/arm32/livepatch.c  |  7 +++++++
     xen/arch/arm/arm64/livepatch.c  |  7 +++++++
     xen/arch/x86/livepatch.c        |  7 +++++++
     xen/common/livepatch.c          | 16 +++++++++++-----
     xen/common/livepatch_elf.c      |  6 ++++++
     xen/include/xen/livepatch_elf.h |  3 ++-
     6 files changed, 40 insertions(+), 6 deletions(-)

    --
    2.34.1

I checked the x86 part and confirmed that my previously non-working livepatch 
loads now.

Tested-by: Bjoern Doebel <doebel@xxxxxxxxx>




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