linux-kernel - Re: [PATCH 2/2] x86/kvmclock: set_memory

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Date:   Tue, 22 Jan 2019 21:43:39 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ram Pai <linuxram@...ibm.com>
Subject: Re: [PATCH 2/2] x86/kvmclock: set_memory_decrypted() takes number of
 pages

On 1/22/19 3:17 PM, Thiago Jung Bauermann wrote:
> From: Ram Pai <linuxram@...ibm.com>
> 
> set_memory_decrypted() expects the number of PAGE_SIZE pages to decrypt.
> kvmclock_init_mem() instead passes number of bytes. This decrypts a huge
> number of pages resulting in data corruption.

Same comment as patch 1/2 in this series.  This is not correct. See
comments below.

> 
> Fixed it.
> 
> [ bauermann: Slightly reworded commit message and added Fixes: tag. ]
> Fixes: 6a1cac56f41f ("x86/kvm: Use __bss_decrypted attribute in shared variables")
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> ---
>  arch/x86/kernel/kvmclock.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> Note: Found by code inspection. I don't have a way to test.
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index e811d4d1c824..b5c867dd2c8d 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -251,8 +251,7 @@ static void __init kvmclock_init_mem(void)
>  	 * be mapped decrypted.
>  	 */
>  	if (sev_active()) {
> -		r = set_memory_decrypted((unsigned long) hvclock_mem,
> -					 1UL << order);
> +		r = set_memory_decrypted((unsigned long) hvclock_mem, 1);

Again, not correct. A number of pages were allocated based on the order.
That number is calculated using the shift in the call. Hardcoding this to
1 is wrong.

Thanks,
Tom

>  		if (r) {
>  			__free_pages(p, order);
>  			hvclock_mem = NULL;
>