Re: [PATCH v9 42/43] virt: sevguest: Add support to derive key
From: Brijesh Singh
Date: Mon Feb 07 2022 - 15:10:01 EST
On 2/7/22 1:09 PM, Dov Murik wrote:
On 07/02/2022 18:23, Brijesh Singh wrote:
On 2/7/22 2:52 AM, Borislav Petkov wrote:
Those are allocated on stack, why are you clearing them?
Yep, no need to explicitly clear it. I'll take it out in next rev.
Wait, this is key material generated by PSP and passed to userspace.
Why leave copies of it floating around kernel memory? I thought that's
the whole reason for these memzero_explicit() calls (maybe add a comment?).
Ah, now I remember I added the memzero_explicit() to address your review
feedback :) In that patch version, we were using the kmalloc() to store
the response data; since then, we switched to stack. We will leak the
key outside when the stack is converted private-> shared; I don't know
if any of these are going to happen. I can add a comment and keep the
memzero_explicit() call.
Boris, let me know if you are okay with it?
As an example, in arch/x86/crypto/aesni-intel_glue.c there are two calls
to memzero_explicit(), both on stack variables; the only reason for
these calls (as I understand it) is to avoid some future possible leak
of this sensitive data (keys, cipher context, etc.). I'm sure there are
other examples in the kernel code.