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Date:   Wed, 28 Apr 2021 13:33:06 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v26 6/9] x86/vdso: Insert endbr32/endbr64 to vDSO
Message-ID: <202104281332.94A153C@keescook>
References: <20210427204720.25007-1-yu-cheng.yu@intel.com>
 <20210427204720.25007-7-yu-cheng.yu@intel.com>
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In-Reply-To: <20210427204720.25007-7-yu-cheng.yu@intel.com>
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On Tue, Apr 27, 2021 at 01:47:17PM -0700, Yu-cheng Yu wrote:
> From: "H.J. Lu" <hjl.tools@gmail.com>
> 
> When Indirect Branch Tracking (IBT) is enabled, vDSO functions may be
> called indirectly, and must have ENDBR32 or ENDBR64 as the first
> instruction.  The compiler must support -fcf-protection=branch so that it
> can be used to compile vDSO.

If you respin this, you can maybe rephrase this since CONFIG_X86_IBT
has already tested for the compiler support.

> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> v24:
> - Replace CONFIG_X86_CET with CONFIG_X86_IBT to reflect splitting of shadow
>   stack and ibt.
> 
>  arch/x86/entry/vdso/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 05c4abc2fdfd..a773a5f03b63 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -93,6 +93,10 @@ endif
>  
>  $(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
>  
> +ifdef CONFIG_X86_IBT
> +$(vobjs) $(vobjs32): KBUILD_CFLAGS += -fcf-protection=branch
> +endif
> +
>  #
>  # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
>  #
> -- 
> 2.21.0
> 

-- 
Kees Cook