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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id a14sm1718704pgw.27.2022.02.10.16.56.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Feb 2022 16:56:56 -0800 (PST) Date: Thu, 10 Feb 2022 16:56:55 -0800 From: Kees Cook To: Michael Ellerman Cc: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Andrew Morton , "James E.J. Bottomley" , Helge Deller , Arnd Bergmann , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3 08/12] asm-generic: Refactor dereference_[kernel]_function_descriptor() Message-ID: <202202101655.13C794F0F@keescook> References: <93a2006a5d90292baf69cb1c34af5785da53efde.1634457599.git.christophe.leroy@csgroup.eu> <8735kr814c.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8735kr814c.fsf@mpe.ellerman.id.au> Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=M5RXsM8h; spf=pass (imf27.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.45 as permitted sender) smtp.mailfrom=keescook@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspamd-Server: rspam07 X-Rspam-User: X-Rspamd-Queue-Id: CD41140004 X-Stat-Signature: niit6u7ut6qjxdeniwhne35eegcfnqky X-HE-Tag: 1644541017-631323 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Feb 10, 2022 at 09:30:43PM +1100, Michael Ellerman wrote: > Christophe Leroy writes: > > diff --git a/kernel/extable.c b/kernel/extable.c > > index b0ea5eb0c3b4..1ef13789bea9 100644 > > --- a/kernel/extable.c > > +++ b/kernel/extable.c > > @@ -159,12 +160,32 @@ int kernel_text_address(unsigned long addr) > > } > > > > /* > > - * On some architectures (PPC64, IA64) function pointers > > + * On some architectures (PPC64, IA64, PARISC) function pointers > > * are actually only tokens to some data that then holds the > > * real function address. As a result, to find if a function > > * pointer is part of the kernel text, we need to do some > > * special dereferencing first. > > */ > > +#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS > > +void *dereference_function_descriptor(void *ptr) > > +{ > > + func_desc_t *desc = ptr; > > + void *p; > > + > > + if (!get_kernel_nofault(p, (void *)&desc->addr)) > > + ptr = p; > > + return ptr; > > +} > > This needs an EXPORT_SYMBOL_GPL(), otherwise the build breaks after > patch 10 with CONFIG_LKDTM=m. Oh good catch! (There have been a few cases of LKDTM=m being the only thing needed a symbol, so I've pondered giving it a namespace or constructing a little ifdef wrapper... but this seems ok to export...) -- Kees Cook