linux-stable.git/arch/um/kernel/process.c, branch v6.14

um: avoid copying FP state from init_task

2025-02-12T22:40:38+00:00

The init_task instance of struct task_struct is statically allocated and
does not contain the dynamic area for the userspace FP registers. As
such, limit the copy to the valid area of init_task and fill the rest
with zero.

Note that the FP state is only needed for userspace, and as such it is
entirely reasonable for init_task to not contain it.

Reported-by: Brian Norris 
Closes: https://lore.kernel.org/Z1ySXmjZm-xOqk90@google.com
Fixes: 3f17fed21491 ("um: switch to regset API and depend on XSTATE")
Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241217202745.1402932-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg 
Signed-off-by: Richard Weinberger

um: Remove unused user_context function

2025-01-10T12:49:57+00:00

It's no longer used since commit 6aa802ce6acc ("uml: throw out
CHOOSE_MODE").

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20241128083137.2219830-10-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg

um: move thread info into task

2024-11-12T13:50:31+00:00

This selects the THREAD_INFO_IN_TASK option for UM and changes the way
that the current task is discovered. This is trivial though, as UML
already tracks the current task in cpu_tasks[] and this can be used to
retrieve it.

Also remove the signal handler code that copies the thread information
into the IRQ stack. It is obsolete now, which also means that the
mentioned race condition cannot happen anymore.

Signed-off-by: Benjamin Berg 
Reviewed-by: Hajime Tazaki 
Link: https://patch.msgid.link/20241111102910.46512-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: switch to regset API and depend on XSTATE

2024-10-23T10:13:16+00:00

The PTRACE_GETREGSET API has now existed since Linux 2.6.33. The XSAVE
CPU feature should also be sufficiently common to be able to rely on it.

With this, define our internal FP state to be the hosts XSAVE data. Add
discovery for the hosts XSAVE size and place the FP registers at the end
of task_struct so that we can adjust the size at runtime.

Next we can implement the regset API on top and update the signal
handling as well as ptrace APIs to use them. Also switch coredump
creation to use the regset API and finally set HAVE_ARCH_TRACEHOOK.

This considerably improves the signal frames. Previously they might not
have contained all the registers (i386) and also did not have the
sizes and magic values set to the correct values to permit userspace to
decode the frame.

As a side effect, this will permit UML to run on hosts with newer CPU
extensions (such as AMX) that need even more register state.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241023094120.4083426-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: remove auxiliary FP registers

2024-10-10T10:10:30+00:00

We do not need the extra save/restore of the FP registers when getting
the fault information. This was originally added in commit 2f56debd77a8
("uml: fix FP register corruption") but at that time the code was not
saving/restoring the FP registers when switching to userspace. This was
fixed in commit fbfe9c847edf ("um: Save FPU registers between task
switches") and since then the auxiliary registers have not been useful.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241004233821.2130874-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: always use the internal copy of the FP registers

2024-10-10T10:03:55+00:00

When switching from userspace to the kernel, all registers including the
FP registers are copied into the kernel and restored later on. As such,
the true source for the FP register state is actually already in the
kernel and they should never be grabbed from the userspace process.

Change the various places to simply copy the data from the internal FP
register storage area. Note that on i386 the format of PTRACE_GETFPREGS
and PTRACE_GETFPXREGS is different enough that conversion would be
needed. With this patch, -EINVAL is returned if the non-native format is
requested.

The upside is, that this patchset fixes setting registers via ptrace
(which simply did not work before) as well as fixing setting floating
point registers using the mcontext on signal return on i386.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20240913133845.964292-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: Fix the return value of elf_core_copy_task_fpregs

2024-10-10T10:02:40+00:00

This function is expected to return a boolean value, which should be
true on success and false on failure.

Fixes: d1254b12c93e ("uml: fix x86_64 core dump crash")
Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20240913023302.130300-1-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg

um: Remove unused fields from thread_struct

2024-09-12T18:35:35+00:00

These fields are no longer used since the removal of tt mode.

Signed-off-by: Tiwei Bie 
Signed-off-by: Richard Weinberger

um: remove force_flush_all from fork_handler

2024-07-03T15:09:50+00:00

There should be no need for this. It may be that this used to work
around another issue where after a clone the MM was in a bad state.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20240703134536.1161108-11-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: Remove /proc/sysemu support code

2024-07-03T10:21:57+00:00

Currently /proc/sysemu will never be registered, as sysemu_supported
is initialized to zero implicitly and no code updates it. And there is
also nothing to configure via sysemu in UML anymore.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20240527134024.1539848-3-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg