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bhyve: allow reading of fwctl signature multiple times

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At the moment, you only have one single chance to read the fwctl
signature. At boot bhyve is in the state IDENT_WAIT. It's then
possible to switch to IDENT_SEND. After bhyve sends the signature,
it switches to REQ. From now on it's impossible to switch back to
IDENT_SEND to read the signature. For that reason, only a single
driver can read the signature. A guest can't use two drivers to
identify that fwctl is present. It gets even worse when using
OVMF. OVMF uses a library to access fwctl. Therefore, every single
OVMF driver would try to read the signature. Currently, only a
single OVMF driver accesses the fwctl. So, there's no issue with
it yet. However, no OS driver would have a chance to detect fwctl when
using OVMF because it's signature was already consumed by OVMF.

Reviewed by:    markj
MFC after:      2 weeks
Sponsored by:   Beckhoff Automation GmbH & Co. KG
Differential Revision:  https://reviews.freebsd.org/D31981
This commit is contained in:
Corvin Köhne 2022-01-03 14:18:31 +01:00 committed by Emmanuel Vadot
parent 01f9362ef4
commit 8ec366ec6c
1 changed files with 12 additions and 10 deletions
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22
usr.sbin/bhyve/fwctl.c
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@ -472,16 +472,18 @@ fwctl_inb(void)
static void
fwctl_outw(uint16_t val)
{
switch (be_state) {
case IDENT_WAIT:
if (val == 0) {
be_state = IDENT_SEND;
ident_idx = 0;
}
break;
default:
/* ignore */
break;
if (be_state == DORMANT) {
return;
}
if (val == 0) {
/*
* The guest wants to read the signature. It's possible that the
* guest is unaware of the fwctl state at this moment. For that
* reason, reset the state machine unconditionally.
*/
be_state = IDENT_SEND;
ident_idx = 0;
}
}