This is a reboot of my original series to address the problem of drivers for legacy ISA devices accessing unmapped IO port regions on arm64 systems and causing the system to crash.
There was another recent report of such an issue [0], and some old ones [1] and [2] for reference.
The background is that many systems do not include PCI host controllers, or they do and controller probe may have failed. For these cases, no IO ports are mapped. However, loading drivers for legacy ISA devices can crash the system as there is nothing to stop them accessing those IO ports (which have not been io remap'ed).
My original solution tried to keep the kernel alive in these situations by rejecting logical PIO access to PCI IO regions until PCI IO port regions have been mapped.
This series goes one step further, by just reserving the complete legacy IO port range in 0x0--0xffff for arm64. The motivation for doing this is to make the request_region() calls for those drivers fail, like this:
root@ubuntu:/home/john# insmod mk712.ko [ 3415.575800] mk712: unable to get IO region insmod: ERROR: could not insert module mk712.ko: No such device
Otherwise, in theory, those drivers could initiate rogue accesses to mapped IO port regions for other devices and cause corruptions or side-effects. Indeed, those drivers should not be allowed to access IO ports at all in such a system.
As a secondary defence, for broken drivers who do not call request_region(), IO port accesses in range 0--0xffff will be ignored, again preserving the system.
I am sending as an RFC as I am not sure of any problem with reserving first 0x10000 of IO space like this. There is reserve= commandline argument, which does allow this already.
For reference, here's how /proc/ioports looks on my arm64 system with this change:
root@ubuntu:/home/john# more /proc/ioports 00010000-0001ffff : PCI Bus 0002:f8 00010000-00010fff : PCI Bus 0002:f9 00010000-00010007 : 0002:f9:00.0 00010000-00010007 : serial 00010008-0001000f : 0002:f9:00.1 00010008-0001000f : serial 00010010-00010017 : 0002:f9:00.2 00010018-0001001f : 0002:f9:00.2 00020000-0002ffff : PCI Bus 0004:88 00030000-0003ffff : PCI Bus 0005:78 00040000-0004ffff : PCI Bus 0006:c0 00050000-0005ffff : PCI Bus 0007:90 00060000-0006ffff : PCI Bus 000a:10 00070000-0007ffff : PCI Bus 000c:20 00080000-0008ffff : PCI Bus 000d:30
[0] https://lore.kernel.org/linux-input/20210112055129.7840-1-song.bao.hua@hisil... [1] https://lore.kernel.org/linux-pci/56F209A9.4040304@huawei.com [2] https://lore.kernel.org/linux-arm-kernel/e6995b4a-184a-d8d4-f4d4-9ce75d8f47c...
Difference since v4: https://lore.kernel.org/linux-pci/1560262374-67875-1-git-send-email-john.gar... - Reserve legacy ISA region
John Garry (4): arm64: io: Introduce IO_SPACE_BASE asm-generic/io.h: Add IO_SPACE_BASE kernel/resource: Make ioport_resource.start configurable logic_pio: Warn on and discard accesses to addresses below IO_SPACE_BASE
arch/arm64/include/asm/io.h | 1 + include/asm-generic/io.h | 4 ++++ include/linux/logic_pio.h | 5 +++++ kernel/resource.c | 2 +- lib/logic_pio.c | 20 ++++++++++++++------ 5 files changed, 25 insertions(+), 7 deletions(-)