linux-kernel - Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve

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Date:   Wed, 16 Nov 2016 18:54:37 +0100
From:   Borislav Petkov <bp@...e.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>,
        Andy Lutomirski <luto@...nel.org>,
        David Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve

On Wed, Nov 16, 2016 at 08:56:36AM -0800, Yu-cheng Yu wrote:
> Robert O'Callahan reported that after an execve PTRACE_GETREGSET
> NT_X86_XSTATE continues to return the pre-exec register values
> until the exec'ed task modifies FPU state.  The test code is at
> https://bugzilla.redhat.com/attachment.cgi?id=1164286.
> 
> What is happening is when eagerfpu is enabled, fpu__clear() did
> not properly clear fpstate.  Fix it by doing just that.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Reported-by: Robert O'Callahan <robert@...llahan.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: David Hansen <dave.hansen@...ux.intel.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
> ---
>  arch/x86/kernel/fpu/core.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 4700401..4c203c4 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -521,14 +521,14 @@ void fpu__clear(struct fpu *fpu)
>  {
>  	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
>  
> -	if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
> -		/* FPU state will be reallocated lazily at the first use. */
> -		fpu__drop(fpu);
> -	} else {
> -		if (!fpu->fpstate_active) {
> -			fpu__activate_curr(fpu);
> -			user_fpu_begin();
> -		}
> +	fpu__drop(fpu);
> +
> +	/*
> +	 * When eagerfpu is used, make sure fpstate is cleared and initialized.
> +	 */
> +	if (use_eager_fpu()) {

c592b5734706 ("x86/fpu: Remove use_eager_fpu()")

Please redo this patch against tip/master.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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