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

[Thomas Gleixner]

Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> 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