linux-kernel - Re: [PATCH 2/4] x86/platform/UV: Fix problem with bad UV4 EFI System Table causing panic

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Date:	Fri, 29 Jul 2016 13:17:09 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mike Travis <travis@....com>
cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dimitri Sivanich <sivanich@....com>,
	Russ Anderson <rja@....com>,
	John Estabrook <estabrook@....com>,
	Andrew Banman <abanman@....com>,
	Nathan Zimmer <nzimmer@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/platform/UV: Fix problem with bad UV4 EFI System
 Table causing panic

On Wed, 27 Jul 2016, Mike Travis wrote:

> Fix a problem that occurs if for some reason the UV4 EFI System Table
> is not available, the check inadvertantly can cause a panic.
> 
> Reviewed-by: Dimitri Sivanich <sivanich@....com>
> Reviewed-by: Nathan Zimmer <nzimmer@....com>
> Tested-by: Frank Ramsay <framsay@....com>
> Tested-by: John Estabrook <estabrook@....com>
> Signed-off-by: Mike Travis <travis@....com>
> ---
>  arch/x86/platform/uv/bios_uv.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> --- linux-3.12.orig/arch/x86/platform/uv/bios_uv.c
> +++ linux-3.12/arch/x86/platform/uv/bios_uv.c
> @@ -201,11 +201,12 @@ void uv_bios_init(void)
>  	}
>  
>  	if (uv_systab->revision >= UV_SYSTAB_VERSION_UV4) {
> +		int size = uv_systab->size;
> +
>  		iounmap(uv_systab);
> -		uv_systab = ioremap(efi.uv_systab, uv_systab->size);

I think the changelog is bogus. What's happening here is a classic use after
unmap, which you avoid by this change.

> +		uv_systab = ioremap(efi.uv_systab, size);

Hmm?

	tglx