linux-kernel - Re: [PATCH v3 12/19] x86, kaslr: Fix a bug that relocation can not be handled when kernel is loaded above 2G

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Message-ID: <CAGXu5jJeqvGq-9yBDBCEGcAfw4-=yGn2JQfMynFs2_MFj51HpQ@mail.gmail.com>
Date:	Mon, 7 Mar 2016 15:30:02 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Vivek Goyal <vgoyal@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v3 12/19] x86, kaslr: Fix a bug that relocation can not be
 handled when kernel is loaded above 2G

On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@...hat.com> wrote:
> When process 32 bit relocation tables a local variable 'extended'
> is defined to calculate the physical address of relocs entry.
> However its type is 'int' which is enough for i386, but not enough
> for x86_64. That's why relocation can only be handled under 2G.
> Otherwise a overflow will happen and cause system hang.
>
> Here change it to 'long' as 32 bit inverse relocation processing
> does, and this change is safe for i386 relocation handling.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>

Acked-by: Kees Cook <keescook@...omium.org>

This patch should probably be moved up into the start of this series
instead of living in the middle here, since it's a clear stand-alone
bug fix.

-Kees

> ---
>  arch/x86/boot/compressed/misc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index 4b2cd0c..70445c3 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -298,7 +298,7 @@ static void handle_relocations(void *output, unsigned long output_len)
>          * So we work backwards from the end of the decompressed image.
>          */
>         for (reloc = output + output_len - sizeof(*reloc); *reloc; reloc--) {
> -               int extended = *reloc;
> +               long extended = *reloc;
>                 extended += map;
>
>                 ptr = (unsigned long)extended;
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security