Messages in this thread | | | Subject | Re: [PATCH v9 42/43] virt: sevguest: Add support to derive key | From | Brijesh Singh <> | Date | Mon, 7 Feb 2022 14:08:17 -0600 |
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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. >
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