Re: [PATCH v14 03/13] x86/sev: Add Secure TSC support for SNP guests

["Nikunj A. Dadhania" <nikunj@amd.com>]

On 11/11/2024 5:00 PM, Borislav Petkov wrote:
> On Mon, Nov 11, 2024 at 04:53:30PM +0530, Nikunj A. Dadhania wrote:
>> When snp_msg_alloc() is called by the sev-guest driver, secrets will
>> be reinitialized and buffers will be re-allocated, leaking memory
>> allocated during snp_get_tsc_info()::snp_msg_alloc(). 
> 
> Huh?
> 
> How do you leak memory when you clear all buffers before that?!?

Memory allocated for the request, response and certs_data is not
freed and we will clear the mdesc when sev-guest driver calls
snp_msg_alloc().

Let me try again to explain what I mean:

snp_msg_alloc() will be called by snp_get_tsc_info() and later by
sev-guest driver.

snp_prepare_tsc()
 ->snp_get_tsc_info()
    ->snp_msg_alloc()
      -> clears mdesc
      ->ioremaps secrets_pa
      ->request = alloc_shared_pages()
                   -> alloc_pages()
      ->response = alloc_shared_pages()
                    -> alloc_pages()
      ->certs_data = alloc_shared_pages()
                      -> alloc_pages()


sev-guest driver
sev_guest_probe()
 ->snp_msg_alloc()
   ->clears mdesc
   ->ioremaps secrets_pa
   ->request = alloc_shared_pages()
                -> alloc_pages()
   ->response = alloc_shared_pages()
                 -> alloc_pages()
   ->certs_data = alloc_shared_pages()
                   -> alloc_pages()

request, response and certs_data are re-allocated. Am I missing something ?

Regards
Nikunj