We rely on errno to determine whether a syscall has failed, so we
need to ensure that accessing errno is async-signal-safe. Currently,
we preserve the errno in sig_handler_common(), but it doesn't cover
every possible case. Let's do it in hard_handler() instead, which
is the signal handler we actually register.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260106001228.1531146-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Inheriting the vDSO from the host is problematic. The values read
from the time functions will not be correct for the UML kernel.
Furthermore the start and end of the vDSO are not stable or
detectable by userspace. Specifically the vDSO datapages start
before AT_SYSINFO_EHDR and the vDSO itself is larger than a single page.
This codepath is only used on 32bit x86 UML. In my testing with both
32bit and 64bit hosts the passthrough functionality has always been
disabled anyways due to the checks against envp in scan_elf_aux().
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-4-e930063eff5f@weissschuh.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Add initial symmetric multi-processing (SMP) support to UML. With
this support enabled, users can tell UML to start multiple virtual
processors, each represented as a separate host thread.
In UML, kthreads and normal threads (when running in kernel mode)
can be scheduled and executed simultaneously on different virtual
processors. However, the userspace code of normal threads still
runs within their respective single-threaded stubs.
That is, SMP support is currently available both within the kernel
and across different processes, but still remains limited within
threads of the same process in userspace.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20251027001815.1666872-6-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
With SMP and NO_HZ enabled, the CPU may still need to sleep even
if the timer is disarmed. Switch to deciding whether to sleep based
on pending resched. Additionally, because disabling IRQs does not
block SIGALRM, it is also necessary to check for any pending timer
alarms. This is a preparation for adding SMP support.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20251027001815.1666872-4-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
The file-based iomem emulation was introduced to support writing
paravirtualized drivers based on emulated iomem regions. However,
the only driver that makes use of it is an example driver called
mmapper, which was written over two decades ago.
We now have several modern device emulation mechanisms, such as
vhost-user-based virtio-uml. Remove the file-based iomem emulation
support to reduce the maintenance burden.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20251027054519.1996090-5-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Pull uml updates from Johannes Berg:
- minor preparations for SMP support
- SPARSE_IRQ support for kunit
- help output cleanups
* tag 'uml-for-linux-6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/uml/linux:
um: Remove unused ipi_pipe field from cpuinfo_um
um: Remove unused cpu_data and current_cpu_data macros
um: Stop tracking virtual CPUs via mm_cpumask()
um: Centralize stub size calculations
um: Remove outdated comment about STUB_DATA_PAGES
um: Remove unused offset and child_err fields from stub_data
um: Indent time-travel help messages
um: Fix help message for ssl-non-raw
um: vector: Fix indentation for help message
um: Add missing trailing newline to help messages
um: virtio-pci: implement .shutdown()
um: Support SPARSE_IRQ
When copying FDs, the copy size should not include the control
message header (cmsghdr). Fix it.
Fixes: 5cde6096a4 ("um: generalize os_rcv_fd")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
On one of my machines UML failed to start after enabling
SELinux.
UML failed to start because SELinux's execmod rule denies
executable pages on a modified file mapping.
Historically UML marks it's stack rwx.
AFAICT, these days this is no longer needed, so let's remove
PROT_EXEC.
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Some help messages are missing a trailing newline. They should
end with two newlines, but only one is present. Add the missing
newline to make the --help output more readable.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
There was a typo that caused the extended FP state to be copied into the
wrong location on 32 bit. On 32 bit we only store the xstate internally
as that already contains everything. However, for compatibility, the
mcontext on 32 bit first contains the legacy FP state and then the
xstate.
The code copied the xstate on top of the legacy FP state instead of
using the correct offset. This offset was already calculated in the
xstate_* variables, so simply switch to those to fix the problem.
With this SECCOMP mode works on 32 bit, so lift the restriction.
Fixes: b1e1bd2e69 ("um: Add helper functions to get/set state for SECCOMP")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250604081705.934112-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Instead of always sharing the FDs with the userspace process, only hand
over the FDs needed for mmap when required. The idea is that userspace
might be able to force the stub into executing an mmap syscall, however,
it will not be able to manipulate the control flow sufficiently to have
access to an FD that would allow mapping arbitrary memory.
Security wise, we need to be sure that only the expected syscalls are
executed after the kernel sends FDs through the socket. This is
currently not the case, as userspace can trivially jump to the
rt_sigreturn syscall instruction to execute any syscall that the stub is
permitted to do. With this, it can trick the kernel to send the FD,
which in turn allows userspace to freely map any physical memory.
As such, this is currently *not* secure. However, in principle the
approach should be fine with a more strict SECCOMP filter and a careful
review of the stub control flow (as userspace can prepare a stack). With
some care, it is likely possible to extend the security model to SMP if
desired.
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250602130052.545733-8-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This detects seccomp support, sets the global using_seccomp variable and
initilizes the exec registers. The support is only enabled if the
seccomp= kernel parameter is set to either "on" or "auto". With "auto" a
fallback to ptrace mode will happen if initialization failed.
Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250602130052.545733-7-benjamin@sipsolutions.net
[extend help with Kconfig text from v2, use exit syscall instead of libc,
remove unneeded mctx_offset assignment, disable on 32-bit for now]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
