Re: [tip:x86/pti] module/retpoline: Warn about missing retpoline in module

[Borislav Petkov]

On Fri, Jan 26, 2018 at 06:59:06AM -0800, tip-bot for Andi Kleen wrote:
> Commit-ID:  caf7501a1b4ec964190f31f9c3f163de252273b8
> Gitweb:     https://git.kernel.org/tip/caf7501a1b4ec964190f31f9c3f163de252273b8
> Author:     Andi Kleen <ak@xxxxxxxxxxxxxxx>
> AuthorDate: Thu, 25 Jan 2018 15:50:28 -0800
> Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CommitDate: Fri, 26 Jan 2018 15:03:56 +0100
> 
> module/retpoline: Warn about missing retpoline in module
> 
> There's a risk that a kernel which has full retpoline mitigations becomes
> vulnerable when a module gets loaded that hasn't been compiled with the
> right compiler or the right option.
> 
> To enable detection of that mismatch at module load time, add a module info
> string "retpoline" at build time when the module was compiled with
> retpoline support. This only covers compiled C source, but assembler source
> or prebuilt object files are not checked.
> 
> If a retpoline enabled kernel detects a non retpoline protected module at
> load time, print a warning and report it in the sysfs vulnerability file.
> 
> [ tglx: Massaged changelog ]
> 
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx
> Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
> Cc: jeyu@xxxxxxxxxx
> Cc: arjan@xxxxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/20180125235028.31211-1-andi@xxxxxxxxxxxxxx
> ---
>  arch/x86/kernel/cpu/bugs.c | 17 ++++++++++++++++-
>  include/linux/module.h     |  9 +++++++++
>  kernel/module.c            | 11 +++++++++++
>  scripts/mod/modpost.c      |  9 +++++++++
>  4 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 390b3dc..4a39d7b 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -11,6 +11,7 @@
>  #include <linux/init.h>
>  #include <linux/utsname.h>
>  #include <linux/cpu.h>
> +#include <linux/module.h>
>  
>  #include <asm/nospec-branch.h>
>  #include <asm/cmdline.h>
> @@ -93,6 +94,19 @@ static const char *spectre_v2_strings[] = {
>  #define pr_fmt(fmt)     "Spectre V2 mitigation: " fmt
>  
>  static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
> +static bool spectre_v2_bad_module;

allnoconfig says:

arch/x86/kernel/cpu/bugs.c:97:13: warning: âspectre_v2_bad_moduleâ defined but not used [-Wunused-variable]
 static bool spectre_v2_bad_module;
             ^

-- 
Regards/Gruss,
    Boris.

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