libFuzzer triggered the following assertion:
cat << EOF | qemu-system-i386 -M pc-q35-5.0 \
-nographic -monitor none -serial none \
-qtest stdio -d guest_errors -trace pci\*
outl 0xcf8 0x8400f841
outl 0xcfc 0xebed205d
outl 0x5d02 0xedf82049
EOF
pci_cfg_write ICH9-LPC 31:0 @0x41 <- 0xebed205d
hw/pci/pci.c:268: int pci_bus_get_irq_level(PCIBus *, int): Assertion `irq_num < bus->nirq' failed.
This is because ich9_lpc_sci_irq() returns -1 for reserved
(illegal) values, but ich9_lpc_pmbase_sci_update() considers
it valid and store it in a 8-bit unsigned type. Then the 255
value is used as GSI IRQ, resulting in a PIRQ value of 247,
more than ICH9_LPC_NB_PIRQS (8).
Fix by simply ignoring the invalid access (and reporting it):
pci_cfg_write ICH9-LPC 31:0 @0x41 <- 0xebed205d
ICH9 LPC: SCI IRQ SEL #3 is reserved
pci_cfg_read mch 00:0 @0x0 -> 0x8086
pci_cfg_read mch 00:0 @0x0 -> 0x29c08086
...
Cc: qemu-stable@nongnu.org
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Fixes: 8f242cb724 ("ich9: implement SCI_IRQ_SEL register")
BugLink: https://bugs.launchpad.net/qemu/+bug/1878642
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200717151705.18611-1-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
4177b062fc