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Wed, 16 Jun 2021 23:50:02 +1000 (AEST) Received: by mail.kernel.org (Postfix) with ESMTPSA id 2007961356; Wed, 16 Jun 2021 13:49:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623851398; bh=F+0AD/z32n3IQAOZXMGGWEtpwRyURijw8GdpAQNt9m0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BWjCeUb525061FgtkOt8wAR3RbNoQldRkdI/xLeNzVqQvHjBrWawgoiajz3wAQamB BupbE5wm/JDrDZvgxYELl+BrOrA3celdzG7Z+Px4+Hl0GkkyReyjaNQsAfGZaLMDqG mNIbUowbXBxrkE2NDVK/B3dN/OxVKxqbZ9lOnjytdMpeWZ/8xantSlUinrEtCVkxnI EyMhUKEAkIumc5AeiaeoenQSHtxqNsQxN7rHqm//i29Ql9bxQMuzXwoMW7nWYB0hCc 7QRLLUVGQkcRYFhmEXgzjGkQHrBN7aODomv6gzXuiCEvv2S9GmfyS5KEp9sdHhB5mm 9BFySz9jHmLeA== Date: Wed, 16 Jun 2021 15:49:54 +0200 From: Jessica Yu To: Michael Ellerman Subject: Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks Message-ID: References: <20210611093959.821525-1-npiggin@gmail.com> <20210611093959.821525-2-npiggin@gmail.com> <1623722110.amu32mwaqs.astroid@bobo.none> <87v96esffr.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <87v96esffr.fsf@mpe.ellerman.id.au> X-OS: Linux linux.fritz.box 5.12.9-1-default x86_64 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Michal =?iso-8859-1?Q?Such=E1nek?= , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" +++ Michael Ellerman [16/06/21 12:37 +1000]: >Jessica Yu 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 >>>>>[np: split patch, added changelog] >>>>>Signed-off-by: Nicholas Piggin >>>>>--- >>>>> 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!