linux-kernel - Re: [PATCH] crypto: ccp - Limit memory allocation in SEV_GET

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Message-ID: <762d33dc-b5fd-d1ef-848c-7de3a6695557@google.com>
Date:   Tue, 27 Dec 2022 17:42:31 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
cc:     Peter Gonda <pgonda@...gle.com>, Andy Nguyen <theflow@...gle.com>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, John Allen <john.allen@....com>,
        "Thomas . Lendacky" <thomas.lendacky@....com>
Subject: Re: [PATCH] crypto: ccp - Limit memory allocation in SEV_GET_ID2
 ioctl

On Thu, 15 Dec 2022, Herbert Xu wrote:

> On Wed, Dec 14, 2022 at 12:20:46PM -0800, Peter Gonda wrote:
> > Currently userspace can ask for any uint32 size allocation for the
> > SEV_GET_ID2. Limit this allocation size to the max physically
> > contiguously allocation: MAX_ORDER.
> 
> This is just to silence the alloc_pages warning, right? If so
> how about adding __GFP_NOWARN instead?
> 

The goal was to be more explicit about that, but setting __GFP_NOWARN 
would result in the same functional behavior.  If we're to go that route, 
it would likely be best to add a comment about the limitation.

That said, if AMD would prefer this to be an EINVAL instead of a ENOMEM by 
introducing a more formal limitation on the length that can be used, that 
would be preferred so that we don't need to rely on the page allocator's 
max length to enforce this arbitrarily.