linux-kernel - Re: [PATCH RFC 16/43] x86-64: Use per-cpu stack canary if supported by compiler

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Date:   Mon, 1 May 2023 10:27:53 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>,
        Brian Gerst <brgerst@...il.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        x86@...nel.org, Nathan Chancellor <nathan@...nel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH RFC 16/43] x86-64: Use per-cpu stack canary if supported
 by compiler

On Fri, Apr 28, 2023 at 2:52 AM Hou Wenlong <houwenlong.hwl@...group.com> wrote:
>
> From: Brian Gerst <brgerst@...il.com>
>
> From: Brian Gerst <brgerst@...il.com>
>
> If the compiler supports it, use a standard per-cpu variable for the
> stack protector instead of the old fixed location.  Keep the fixed
> location code for compatibility with older compilers.
>
> [Hou Wenlong: Disable it on Clang, adapt new code change and adapt
> missing GS set up path in pvh_start_xen()]
>
> Signed-off-by: Brian Gerst <brgerst@...il.com>
> Co-developed-by: Hou Wenlong <houwenlong.hwl@...group.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> Cc: Thomas Garnier <thgarnie@...omium.org>
> Cc: Lai Jiangshan <jiangshan.ljs@...group.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>  arch/x86/Kconfig                      | 12 ++++++++++++
>  arch/x86/Makefile                     | 21 ++++++++++++++-------
>  arch/x86/entry/entry_64.S             |  6 +++++-
>  arch/x86/include/asm/processor.h      | 17 ++++++++++++-----
>  arch/x86/include/asm/stackprotector.h | 16 +++++++---------
>  arch/x86/kernel/asm-offsets_64.c      |  2 +-
>  arch/x86/kernel/cpu/common.c          | 15 +++++++--------
>  arch/x86/kernel/head_64.S             | 16 ++++++++++------
>  arch/x86/kernel/vmlinux.lds.S         |  4 +++-
>  arch/x86/platform/pvh/head.S          |  8 ++++++++
>  arch/x86/xen/xen-head.S               | 14 +++++++++-----
>  11 files changed, 88 insertions(+), 43 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 68e5da464b96..55cce8cdf9bd 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -410,6 +410,18 @@ config CC_HAS_SANE_STACKPROTECTOR
>           the compiler produces broken code or if it does not let us control
>           the segment on 32-bit kernels.
>
> +config CC_HAS_CUSTOMIZED_STACKPROTECTOR
> +       bool
> +       # Although clang supports -mstack-protector-guard-reg option, it
> +       # would generate GOT reference for __stack_chk_guard even with
> +       # -fno-PIE flag.
> +       default y if (!CC_IS_CLANG && $(cc-option,-mstack-protector-guard-reg=gs))

Hi Hou,
I've filed this bug against LLVM and will work with LLVM folks at
Intel to resolve:
https://github.com/llvm/llvm-project/issues/62481
Can you please review that report and let me know here or there if I
missed anything? Would you also mind including a link to that in the
comments in the next version of this patch?

Less relevant issues I filed looking at some related codegen:
https://github.com/llvm/llvm-project/issues/62482
https://github.com/llvm/llvm-project/issues/62480

And we should probably look into:
https://github.com/llvm/llvm-project/issues/22476


-- 
Thanks,
~Nick Desaulniers