Re: powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Michael Ellerman <patch-notifications@ellerman.id.au>]

On Tue, 2018-04-10 at 01:22:06 UTC, Michael Ellerman wrote:
> If you build the kernel with CONFIG_RELOCATABLE=n, then install the
> modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
> old modules installed, we crash something like:
> 
>   Unable to handle kernel paging request for data at address 0xd000000018d66cef
>   Faulting instruction address: 0xc0000000021ddd08
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   Modules linked in: x_tables autofs4
>   CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
>   ...
>   NIP check_version.isra.22+0x118/0x170
>   Call Trace:
>     __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
>     resolve_symbol+0xb4/0x150
>     load_module+0x10e8/0x29a0
>     SyS_finit_module+0x110/0x140
>     system_call+0x58/0x6c
> 
> This happens because since commit 71810db27c1c ("modversions: treat
> symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
> handles symbol CRCs differently from a non-relocatable kernel.
> 
> Although it's possible we could try and detect this situation and
> handle it, it's much more robust to simply make the state of
> CONFIG_RELOCATABLE part of the module vermagic.
> 
> Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/73aca179d78eaa11604ba0783a6d8b

cheers