[lkml]   [2019]   [Oct]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH v2 1/3] livepatch: Clear relocation targets on a module removal
On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes wrote:
> Josh reported a bug:
> When the object to be patched is a module, and that module is
> rmmod'ed and reloaded, it fails to load with:
> module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c
> livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
> The livepatch module has a relocation which references a symbol
> in the _previous_ loading of nfsd. When apply_relocate_add()
> tries to replace the old relocation with a new one, it sees that
> the previous one is nonzero and it errors out.
> On ppc64le, we have a similar issue:
> module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
> livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
> He also proposed three different solutions. We could remove the error
> check in apply_relocate_add() introduced by commit eda9cec4c9a1
> ("x86/module: Detect and skip invalid relocations"). However the check
> is useful for detecting corrupted modules.
> We could also deny the patched modules to be removed. If it proved to be
> a major drawback for users, we could still implement a different
> approach. The solution would also complicate the existing code a lot.
> We thus decided to reverse the relocation patching (clear all relocation
> targets on x86_64, or return back nops on powerpc). The solution is not
> universal and is too much arch-specific, but it may prove to be simpler
> in the end.
> Reported-by: Josh Poimboeuf <>
> Signed-off-by: Miroslav Benes <>

Since we decided to fix late module patching at LPC, the commit message
and clear_relocate_add() should both probably clarify that these
functions are hacks which are relatively temporary, until we fix the
root cause.

But this patch gives me a bad feeling :-/ Not that I have a better

Has anybody seen this problem in the real world? If not, maybe we'd be
better off just pretending the problem doesn't exist for now.


 \ /
  Last update: 2019-10-02 20:19    [W:0.107 / U:3.772 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site