On 2/7/22 1:09 PM, Dov Murik wrote:

On 07/02/2022 18:23, Brijesh Singh wrote:

quoted

On 2/7/22 2:52 AM, Borislav Petkov wrote:

quoted

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.