Messages in this thread | | | Date | Wed, 11 Sep 2019 17:40:13 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] module: Fix link failure due to invalid relocation on namespace offset |
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On Wed, Sep 11, 2019 at 03:35:06PM +0200, Jessica Yu wrote: > +++ Will Deacon [11/09/19 13:26 +0100]: > > Commit 8651ec01daed ("module: add support for symbol namespaces.") > > broke linking for arm64 defconfig: > > > > | lib/crypto/arc4.o: In function `__ksymtab_arc4_setkey': > > | arc4.c:(___ksymtab+arc4_setkey+0x8): undefined reference to `no symbol' > > | lib/crypto/arc4.o: In function `__ksymtab_arc4_crypt': > > | arc4.c:(___ksymtab+arc4_crypt+0x8): undefined reference to `no symbol' > > > > This is because the dummy initialisation of the 'namespace_offset' field > > in 'struct kernel_symbol' when using EXPORT_SYMBOL on architectures with > > support for PREL32 locations uses an offset from an absolute address (0) > > in an effort to trick 'offset_to_pointer' into behaving as a NOP, > > allowing non-namespaced symbols to be treated in the same way as those > > belonging to a namespace. > > > > Unfortunately, place-relative relocations require a symbol reference > > rather than an absolute value and, although x86 appears to get away with > > this due to placing the kernel text at the top of the address space, it > > almost certainly results in a runtime failure if the kernel is relocated > > dynamically as a result of KASLR. > > > > Rework 'namespace_offset' so that a value of 0, which cannot occur for a > > valid namespaced symbol, indicates that the corresponding symbol does > > not belong to a namespace. > > > > Cc: Matthias Maennich <maennich@google.com> > > Cc: Jessica Yu <jeyu@kernel.org> > > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > Cc: Catalin Marinas <catalin.marinas@arm.com> > > Fixes: 8651ec01daed ("module: add support for symbol namespaces.") > > Reported-by: kbuild test robot <lkp@intel.com> > > Signed-off-by: Will Deacon <will@kernel.org> > > --- > > > > Please note that I've not been able to test this at LPC, but it's been > > submitted to kernelci. > > Thanks for fixing this so quickly. I can confirm that this fixes the > build for arm64 defconfig and x86 built fine for me as well. I'll wait > a bit and apply this at the end of the day in case Matthias or anybody > else would like to confirm/test.
FWIW, I've managed to boot arm64 Debian under QEMU and load/unload modules successfully with this patch applied on top of modules-next.
Will
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