linux-kernel - Re: [PATCH] x86/fpu/xstate: Clear uninitialized xstate areas in core dump

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87lfm3ehbd.fsf@nanos.tec.linutronix.de>
Date:   Thu, 07 May 2020 20:22:14 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        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>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>, sam <sunhaoyl@...look.com>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/fpu/xstate: Clear uninitialized xstate areas in core dump

Yu-cheng Yu <yu-cheng.yu@...el.com> writes:
> @@ -983,6 +983,7 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
>  {
>  	unsigned int offset, size;
>  	struct xstate_header header;
> +	int last_off;
>  	int i;
>  
>  	/*
> @@ -1006,7 +1007,17 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
>  
>  	__copy_xstate_to_kernel(kbuf, &header, offset, size, size_total);
>  
> +	last_off = 0;
> +
>  	for (i = 0; i < XFEATURE_MAX; i++) {
> +		/*
> +		 * Clear uninitialized area before XSAVE header.
> +		 */
> +		if (i == FIRST_EXTENDED_XFEATURE) {
> +			memset(kbuf + last_off, 0, XSAVE_HDR_OFFSET - last_off);
> +			last_off = XSAVE_HDR_OFFSET + XSAVE_HDR_SIZE;
> +		}
> +
>  		/*
>  		 * Copy only in-use xstates:
>  		 */
> @@ -1020,11 +1031,16 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
>  			if (offset + size > size_total)
>  				break;
>  
> +			memset(kbuf + last_off, 0, offset - last_off);
> +			last_off = offset + size;
> +
>  			__copy_xstate_to_kernel(kbuf, src, offset, size, size_total);
>  		}
>  
>  	}
>  
> +	memset(kbuf + last_off, 0, size_total - last_off);

Why doing all this partial zeroing? There is absolutely no point.

Either the caller clears the buffer or this function clears it right at
the beginning with:

    memset(kbuf, 0, min(size_total, XSAVE_MAX_SIZE));

Thanks,

        tglx