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SubjectRe: [PATCH v1] lkdtm/bugs: fix build error in lkdtm_UNSET_SMEP
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 <brendanhiggins@google.com>

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 <keescook@chromium.org>

-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

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