linux-kernel - Re: [PATCH v26 6/9] x86/vdso: Insert endbr32/endbr64 to vDSO

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Message-ID: <202104281332.94A153C@keescook>
Date:   Wed, 28 Apr 2021 13:33:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>
Subject: Re: [PATCH v26 6/9] x86/vdso: Insert endbr32/endbr64 to vDSO

On Tue, Apr 27, 2021 at 01:47:17PM -0700, Yu-cheng Yu wrote:
> From: "H.J. Lu" <hjl.tools@...il.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@...il.com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>

Reviewed-by: Kees Cook <keescook@...omium.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