Messages in this thread Patch in this message | | | Date | Wed, 16 Jun 2021 15:49:54 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks |
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+++ Michael Ellerman [16/06/21 12:37 +1000]: >Jessica Yu <jeyu@kernel.org> writes: >> +++ Nicholas Piggin [15/06/21 12:05 +1000]: >>>Excerpts from Jessica Yu's message of June 14, 2021 10:06 pm: >>>> +++ Nicholas Piggin [11/06/21 19:39 +1000]: >>>>>The elf_check_arch() function is used to test usermode binaries, but >>>>>kernel modules may have more specific requirements. powerpc would like >>>>>to test for ABI version compatibility. >>>>> >>>>>Add an arch-overridable function elf_check_module_arch() that defaults >>>>>to elf_check_arch() and use it in elf_validity_check(). >>>>> >>>>>Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> >>>>>[np: split patch, added changelog] >>>>>Signed-off-by: Nicholas Piggin <npiggin@gmail.com> >>>>>--- >>>>> include/linux/moduleloader.h | 5 +++++ >>>>> kernel/module.c | 2 +- >>>>> 2 files changed, 6 insertions(+), 1 deletion(-) >>>>> >>>>>diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h >>>>>index 9e09d11ffe5b..fdc042a84562 100644 >>>>>--- a/include/linux/moduleloader.h >>>>>+++ b/include/linux/moduleloader.h >>>>>@@ -13,6 +13,11 @@ >>>>> * must be implemented by each architecture. >>>>> */ >>>>> >>>>>+// Allow arch to optionally do additional checking of module ELF header >>>>>+#ifndef elf_check_module_arch >>>>>+#define elf_check_module_arch elf_check_arch >>>>>+#endif >>>> >>>> Hi Nicholas, >>>> >>>> Why not make elf_check_module_arch() consistent with the other >>>> arch-specific functions? Please see module_frob_arch_sections(), >>>> module_{init,exit}_section(), etc in moduleloader.h. That is, they are >>>> all __weak functions that are overridable by arches. We can maybe make >>>> elf_check_module_arch() a weak symbol, available for arches to >>>> override if they want to perform additional elf checks. Then we don't >>>> have to have this one-off #define. > >>>Like this? I like it. Good idea. >> >> Yeah! Also, maybe we can alternatively make elf_check_module_arch() a >> separate check entirely so that the powerpc implementation doesn't >> have to include that extra elf_check_arch() call. Something like this maybe? > >My thinking for making elf_check_module_arch() the only hook was that >conceivably you might not want/need to call elf_check_arch() from >elf_check_module_arch(). > >So having a single module specific hook allows arch code to decide >how to implement the check, which may or may not involve calling >elf_check_arch(), but that becomes an arch implementation detail.
Thanks for the feedback! Yeah, that's fair too. Well, I ended up doing it this way mostly to create less churn/change of behavior, since in its current state elf_check_arch() is already being called for each arch. Additionally I wanted to save the powerpc implementation of elf_check_module_arch() an extra elf_check_arch() call. In any case I have a slight preference for having a second hook to allow arches add any extra checks in addition to elf_check_arch(). Thanks!
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