linux-kernel - Re: [PATCH] x86/setup: fix low identity map for >= 2GB kernel range

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Date:	Fri, 6 Nov 2015 14:27:33 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Krzysztof Mazur <krzysiek@...lesie.net>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Laszlo Ersek <lersek@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/setup: fix low identity map for >= 2GB kernel range

On Fri, Nov 06, 2015 at 02:18:36PM +0100, Krzysztof Mazur wrote:
> The commit f5f3497cad8c8416a74b9aaceb127908755d020a (x86/setup: Extend
> low identity map to cover whole kernel range) extended the low identity
> mapping. However, if the kernel uses more than 2 GB (VMSPLIT_2G_OPT or
> VMSPLIT_1G memory split), the normal memory mapping is overwritten by
> the low identity mapping causing crash. To avoid overwritting, limit the
> low identity map to cover only memory before kernel range (PAGE_OFFSET).
> 
> Signed-off-by: Krzysztof Mazur <krzysiek@...lesie.net>
> ---
> The bug can be also fixed by copying identity mapping before copying
> kernel address range, but this fix is smaller.
> 
> It might be also helpful to add a warning, if the low identity mapping
> is truncated due to kernel mapping (KERNEL_PGD_BOUNDARY < KERNEL_PGD_PTRS).
> 
>  arch/x86/kernel/setup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index a3cccbf..37c8ea8 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1180,7 +1180,7 @@ void __init setup_arch(char **cmdline_p)
>  	 */
>  	clone_pgd_range(initial_page_table,
>  			swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
> -			KERNEL_PGD_PTRS);
> +			min(KERNEL_PGD_PTRS, KERNEL_PGD_BOUNDARY));
>  #endif
>  
>  	tboot_probe();

http://git.kernel.org/tip/1c5dac914794f0170e1582d8ffdee52d30e0e4dd

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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