git: 99cc129ea469 - stable/13 - bhyve: ignore low bits of CFGADR

The branch stable/13 has been updated by manu:

URL: https://cgit.FreeBSD.org/src/commit/?id=99cc129ea469c59ce75df17cc78eee6dceaca46c

commit 99cc129ea469c59ce75df17cc78eee6dceaca46c
Author:     Corvin Köhne <CorvinK@beckhoff.com>
AuthorDate: 2021-10-15 07:25:54 +0000
Commit:     Emmanuel Vadot <manu@FreeBSD.org>
CommitDate: 2022-01-14 13:51:44 +0000

    bhyve: ignore low bits of CFGADR
    
    Bhyve could emulate wrong PCI registers.
    In the best case, the guest reads wrong registers and the device driver would
    report some errors.
    In the worst case, the guest writes to wrong PCI registers and could brick
    hardware when using PCI passthrough.
    
    According to Intels specification, low bits of CFGADR should be
    ignored. Some OS like linux may rely on it. Otherwise, bhyve could
    emulate a wrong PCI register.
    
    E.g.
    If linux would like to read 2 bytes from offset 0x02, following would
    happen.
    linux:
            outl 0x80000002 at CFGADR
            inw  at CFGDAT + 2
    bhyve:
            cfgoff = 0x80000002 & 0xFF = 0x02
            coff   = cfgoff + (port - CFGDAT) = 0x02 + 0x02 = 0x04
    Bhyve would emulate the register at offset 0x04 not 0x02.
    
    Reviewed By: #bhyve, grehan
    Differential Revision: https://reviews.freebsd.org/D31819
    Sponsored by:          Beckhoff Automation GmbH & Co. KG
    
    (cherry picked from commit 1b0e2f0b607e88feb57accc9521e9623b56ab7e2)
---
 usr.sbin/bhyve/pci_emul.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/usr.sbin/bhyve/pci_emul.c b/usr.sbin/bhyve/pci_emul.c
index d155029d269f..86a2f995126e 100644
--- a/usr.sbin/bhyve/pci_emul.c
+++ b/usr.sbin/bhyve/pci_emul.c
@@ -2018,7 +2018,7 @@ pci_emul_cfgaddr(struct vmctx *ctx, int vcpu, int in, int port, int bytes,
 	} else {
 		x = *eax;
 		cfgenable = (x & CONF1_ENABLE) == CONF1_ENABLE;
-		cfgoff = x & PCI_REGMAX;
+		cfgoff = (x & PCI_REGMAX) & ~0x03;
 		cfgfunc = (x >> 8) & PCI_FUNCMAX;
 		cfgslot = (x >> 11) & PCI_SLOTMAX;
 		cfgbus = (x >> 16) & PCI_BUSMAX;