Ard Biesheuvel <ard.biesheu...@linaro.org> writes:
> On 11 April 2018 at 16:49, Michael Ellerman
> <patch-notificati...@ellerman.id.au> wrote:
>> 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
>>> 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
>>> NIP check_version.isra.22+0x118/0x170
>>> Call Trace:
>>> __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables]
>>> 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 <m...@ellerman.id.au>
>> Applied to powerpc fixes.
> Thanks for the cc. I guess this only affects powerpc, given that it is
> the only arch that switches between CRC immediate values and CRC
> offsets depending on the configuration.
Is there any reason we shouldn't always turn on CONFIG_MODULE_REL_CRCS?
It seems to work, but I wanted to test it more before switching to that,
hence the quick fix above.
arch/um looks like it might be switching based on config, but I don't
know enough to say:
depends on STATIC_LINK
depends on !LD_SCRIPT_STATIC
select MODULE_REL_CRCS if MODVERSIONS