linux-kernel - Re: [PATCH 02/10] xen/pvh: Fix PVHVM 32-bit bootup problems.

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Message-ID: <alpine.DEB.2.02.1210241159230.2689@kaball.uk.xensource.com>
Date:	Wed, 24 Oct 2012 12:01:09 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"mukesh.rathor@...cle.com" <mukesh.rathor@...cle.com>
Subject: Re: [PATCH 02/10] xen/pvh: Fix PVHVM 32-bit bootup problems.

On Tue, 23 Oct 2012, Konrad Rzeszutek Wilk wrote:
> With the split of the 'unsigned int space' in a 'u16 space'
> and 'u16 foreign_domid' in xen_add_to_physmap the compiler
> won't write the full 32-bit value in 'space'. Instead
> it will write a 16-bit value - which is OK. The problem
> is that we allocate the xen_add_to_physmap structure from
> the stack which can (and it has) various garbage on it.
> 
> The end result is that without this patch we end up
> providing this to the hypervisor:
> 
>    xatp.space = 0xc1310001;
> instead of:
>    xatp.space = 0x1;
> 
> Forcing the foreign_domid to 0, will over-write the garbage
> that was on the stack.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

Good fix.


>  arch/x86/xen/enlighten.c  |    1 +
>  drivers/xen/grant-table.c |    1 +
>  2 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index e3497f2..b679f86 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1509,6 +1509,7 @@ void __ref xen_hvm_init_shared_info(void)
>  	xatp.domid = DOMID_SELF;
>  	xatp.idx = 0;
>  	xatp.space = XENMAPSPACE_shared_info;
> +	xatp.foreign_domid = 0;
>  	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
>  	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
>  		BUG();
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index b2b0a37..cbfd929 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -1044,6 +1044,7 @@ static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
>  		do {
>  			xatp.domid = DOMID_SELF;
>  			xatp.idx = i;
> +			xatp.foreign_domid = 0;
>  			xatp.space = XENMAPSPACE_grant_table;
>  			xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
>  			rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
> -- 
> 1.7.7.6
> 
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