linux-kernel - Changes in kernel 5.18-rc1 leads to crashes in VirtualBox Virtual Machines

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Message-ID: <7f01221d-f693-adf8-f5a5-d71944b44162@lwfinger.net>
Date:   Sun, 1 May 2022 12:26:07 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Changes in kernel 5.18-rc1 leads to crashes in VirtualBox Virtual
 Machines

Jason,

I maintain VirtualBox for openSUSE. When kernel 5.18-rc1 was released, I fixed 
the usual set of API changes needed to compile the external kernel modules for 
VB. Despite a clean compile, I am still getting random crashes in the VMs. For 
Linux instances, the desktop disappears, but for Windows guests, the VM crashes 
with unhandled kernel exceptions. As I have no experience tracing such crashes, 
I decided to bisect the kernel to find the commit that started these problems.

Surprisingly, the bisection pointed to commit 6e8ec2552c7d ("random: use 
computational hash for entropy extraction"). I am very sure of the bisection as 
the kernel built from the commit that immediately precedes this one, 
cfb92440ee71 - a tag commit by Linus, runs correctly.

Note that I do not believe there is anything wrong with your changes to the 
random number generators. It seems to be a problem with the way the emulator is 
accessing them. The VirtualBox code is quite complicated, and I am no expert 
with C++.

Are there changes that would be required to the X86_64 emulator's access to the 
random number code as a result of your changes? I have found places where the 
emulator accesses /dev/urandom or /dev/random. There are also places that use 
the rdrand and reseed instructions.

Thanks for reading this,

Larry