linux-kernel - Re: [PATCH] x86/purgatory: Add $(DISABLE_STACKLEAK

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Date:   Mon, 23 Sep 2019 10:25:22 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] x86/purgatory: Add $(DISABLE_STACKLEAK_PLUGIN)

On Mon, Sep 23, 2019 at 10:17 AM Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> Since commit b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than
> reset KBUILD_CFLAGS") kexec breaks is GCC_PLUGIN_STACKLEAK is enabled, as
> the purgatory contains undefined references to stackleak_track_stack.
> Attempting to load a kexec kernel results in:
>         kexec: Undefined symbol: stackleak_track_stack
>         kexec-bzImage64: Loading purgatory failed
>
> Fix this by disabling the stackleak plugin for purgatory.
>
> Fixes: b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS")
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
(Sorry for the fallout from b059f801a937, but this is giving us a
pretty good idea about what "runtime" requirements certain configs
have.  It would be cool to eventually have some kind of kexec test
case that folks could run in QEMU).

> ---
>  arch/x86/purgatory/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 527749066d31..fb4ee5444379 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -25,6 +25,7 @@ KCOV_INSTRUMENT := n
>
>  PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
> +PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)
>
>  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
>  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> --
> 2.21.0
>


-- 
Thanks,
~Nick Desaulniers