[PATCH 03/10] kvmclock: Use free_decrypted_pages()

[PATCH 03/10] kvmclock: Use free_decrypted_pages()

[Rick Edgecombe]

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@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@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;
-- 
2.34.1

Re: [PATCH 03/10] kvmclock: Use free_decrypted_pages()

[Kuppuswamy Sathyanarayanan]

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@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: kvm@vger.kernel.org
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---

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

Otherwise, it looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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

Re: [PATCH 03/10] kvmclock: Use free_decrypted_pages()

[Edgecombe, Rick P]

On Tue, 2023-10-17 at 22:20 -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> 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@redhat.com>
> > Cc: Wanpeng Li <wanpengli@tencent.com>
> > Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> > Cc: kvm@vger.kernel.org
> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > ---
> 
> Since it a fix, do you want to add Fixes tag?
> 
> Otherwise, it looks good to me.
> 
> Reviewed-by: Kuppuswamy Sathyanarayanan
> <sathyanarayanan.kuppuswamy@linux.intel.com>

Thanks. Yes, the thinking was to mark all these for stable, but some
patches are still RFC for this version. I'll add it for all non-RFC
ones in the next version.