linux-kernel - Re: [PATCH 03/10] kvmclock: Use free_decrypted

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Message-ID: <3133a1a5-58c0-4b31-89fe-e86ffa12a342@linux.intel.com>
Date:   Tue, 17 Oct 2023 22:20:25 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, luto@...nel.org,
        peterz@...radead.org, kirill.shutemov@...ux.intel.com,
        elena.reshetova@...el.com, isaku.yamahata@...el.com,
        seanjc@...gle.com, Michael Kelley <mikelley@...rosoft.com>,
        thomas.lendacky@....com, decui@...rosoft.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 03/10] kvmclock: Use free_decrypted_pages()



On 10/17/2023 1:24 PM, Rick Edgecombe wrote:
> On TDX it is possible for the untrusted host to cause
> set_memory_encrypted() or set_memory_decrypted() to fail such that an
> error is returned and the resulting memory is shared. Callers need to take
> care to handle these errors to avoid returning decrypted (shared) memory to
> the page allocator, which could lead to functional or security issues.
> 
> Kvmclock could free decrypted/shared pages if set_memory_decrypted() fails.
> Use the recently added free_decrypted_pages() to avoid this.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Wanpeng Li <wanpengli@...cent.com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: kvm@...r.kernel.org
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---

Since it a fix, do you want to add Fixes tag?

Otherwise, it looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>


>  arch/x86/kernel/kvmclock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index fb8f52149be9..587b159c4e53 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -227,7 +227,7 @@ static void __init kvmclock_init_mem(void)
>  		r = set_memory_decrypted((unsigned long) hvclock_mem,
>  					 1UL << order);
>  		if (r) {
> -			__free_pages(p, order);
> +			free_decrypted_pages((unsigned long)hvclock_mem, order);
>  			hvclock_mem = NULL;
>  			pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
>  			return;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer