linux-kernel - Re: [PATCH v3 06/10] x86/fpu/xstate: Update sanitize_restored

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Date:   Thu, 7 May 2020 15:11:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 06/10] x86/fpu/xstate: Update
 sanitize_restored_xstate() for supervisor xstates

On Sat, Mar 28, 2020 at 09:43:03AM -0700, Yu-cheng Yu wrote:
> The function sanitize_restored_xstate() sanitizes user xstates of an XSAVE
> buffer by setting the buffer's header->xfeatures to the input 'xfeatures',

It doesn't set them to the input xfeatures. I see a "&=" there.

> effectively resetting features not in 'xfeatures' back to the init state.
> 
> When supervisor xstates are introduced, it is necessary to make sure only
> user xstates are sanitized.  Ensure supervisor bits in header->xfeatures
> stay set and supervisor states are not modified.
> 
> To make names clear, also:
> 
> - Rename the function to sanitize_restored_user_xstate().
> - Rename input parameter 'xfeatures' to 'xfeatures_from_user'.
> - In __fpu__restore_sig(), rename 'xfeatures' to 'user_xfeatures'.
> 
> v3:
> - Change xfeatures_user to user_xfeatures.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
>  arch/x86/kernel/fpu/signal.c | 37 +++++++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index cd6eafba12da..d09d72334a12 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -211,9 +211,9 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
>  }
>  
>  static inline void
> -sanitize_restored_xstate(union fpregs_state *state,
> -			 struct user_i387_ia32_struct *ia32_env,
> -			 u64 xfeatures, int fx_only)
> +sanitize_restored_user_xstate(union fpregs_state *state,
> +			      struct user_i387_ia32_struct *ia32_env,
> +			      u64 xfeatures_from_user, int fx_only)

Name those user_xfeatures too.

-- 
Regards/Gruss,
    Boris.

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