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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id g10sm157229pgh.35.2019.12.17.16.14.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Dec 2019 16:14:57 -0800 (PST) Date: Tue, 17 Dec 2019 16:14:56 -0800 From: Kees Cook To: Brendan Higgins Cc: jdike@addtoit.com, richard@nod.at, anton.ivanov@cambridgegreys.com, linux-um@lists.infradead.org, linux-kernel@vger.kernel.org, davidgow@google.com, arnd@arndb.de, gregkh@linuxfoundation.org Subject: Re: [PATCH v1] lkdtm/bugs: fix build error in lkdtm_UNSET_SMEP Message-ID: <201912171613.454319D@keescook> References: <20191213003522.66450-1-brendanhiggins@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20191213003522.66450-1-brendanhiggins@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 12, 2019 at 04:35:22PM -0800, Brendan Higgins wrote: > When building ARCH=um with CONFIG_UML_X86=y and CONFIG_64BIT=y we get > the build errors: > > drivers/misc/lkdtm/bugs.c: In function ‘lkdtm_UNSET_SMEP’: > drivers/misc/lkdtm/bugs.c:288:8: error: implicit declaration of function ‘native_read_cr4’ [-Werror=implicit-function-declaration] > cr4 = native_read_cr4(); > ^~~~~~~~~~~~~~~ > drivers/misc/lkdtm/bugs.c:290:13: error: ‘X86_CR4_SMEP’ undeclared (first use in this function); did you mean ‘X86_FEATURE_SMEP’? > if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { > ^~~~~~~~~~~~ > X86_FEATURE_SMEP > drivers/misc/lkdtm/bugs.c:290:13: note: each undeclared identifier is reported only once for each function it appears in > drivers/misc/lkdtm/bugs.c:297:2: error: implicit declaration of function ‘native_write_cr4’; did you mean ‘direct_write_cr4’? [-Werror=implicit-function-declaration] > native_write_cr4(cr4); > ^~~~~~~~~~~~~~~~ > direct_write_cr4 > > So specify that this block of code should only build when > CONFIG_X86_64=y *AND* CONFIG_UML is unset. > > Signed-off-by: Brendan Higgins Thanks for catching this! Is a similar marking needed for the recently added lkdtm_DOUBLE_FAULT() when using UML on 32-bit? Acked-by: Kees Cook -Kees > --- > > This patch is part of my larger effort to get allyesconfig closer to > working for ARCH=um. For more information about that, checkout the cover > letter for a related patchset here: > > https://lore.kernel.org/lkml/20191211192742.95699-1-brendanhiggins@google.com/ > > --- > drivers/misc/lkdtm/bugs.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c > index a4fdad04809a9..6c1aab177fced 100644 > --- a/drivers/misc/lkdtm/bugs.c > +++ b/drivers/misc/lkdtm/bugs.c > @@ -278,7 +278,7 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void) > > void lkdtm_UNSET_SMEP(void) > { > -#ifdef CONFIG_X86_64 > +#if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) > #define MOV_CR4_DEPTH 64 > void (*direct_write_cr4)(unsigned long val); > unsigned char *insn; > -- > 2.24.1.735.g03f4e72817-goog > -- Kees Cook