kernel/arch/um/os-Linux/registers.c, branch linux-rolling-stable

um: Add SECCOMP support detection and initialization

2025-06-02T14:20:01Z

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 Signed-off-by: Benjamin Berg 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

um: switch to regset API and depend on XSTATE

2024-10-23T10:13:16Z

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 unused register save/restore functions

2024-01-05T15:28:57Z

These functions were only used when calling PTRACE_ARCH_PRCTL, but this code has been removed. Signed-off-by: Benjamin Berg Signed-off-by: Richard Weinberger

um: registers: Rename function names to avoid conflicts and build problems

2021-12-21T20:22:19Z

The function names init_registers() and restore_registers() are used in several net/ethernet/ and gpu/drm/ drivers for other purposes (not calls to UML functions), so rename them. This fixes multiple build errors. Signed-off-by: Randy Dunlap Cc: Jeff Dike Cc: Richard Weinberger Cc: Anton Ivanov Cc: linux-um@lists.infradead.org Signed-off-by: Richard Weinberger

um: Add SPDX headers for files in arch/um/os-Linux

2019-09-15T19:37:17Z

Convert files to use SPDX header. All files are licensed under the GPLv2. Signed-off-by: Alex Dewar Signed-off-by: Richard Weinberger

um: get rid of pointless include "..." where include <...> will do

2012-10-09T20:28:45Z

Signed-off-by: Al Viro Signed-off-by: Richard Weinberger

um: Save FPU registers between task switches

2011-09-15T01:09:37Z

Some time ago Jeff prepared 42daba316557 ("uml: stop saving process FP state") for UML to stop saving the process FP state between task switches. The assumption was that since with SKAS0 every guest process runs inside a host process context the host OS will take care of keeping the proper FP state. Unfortunately this is not true for multi-threaded applications, where all guest threads share a single host process context yet all may use the FPU on their own. Although I haven't verified it I suspect things to be even worse in SKAS3 mode where all guest processes run inside a single host process. The patch reintroduces the saving and restoring of the FP context between task switches. [richard@nod.at: Ingo posted this patch in 2009, sadly it was never applied and got lost. Now in 2011 the problem was reported by Gunnar.] Signed-off-by: Ingo van Lil Signed-off-by: Richard Weinberger Reported-by: Tested-by: Cc: Stanislav Meduna Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

uml: kill processes instead of panicing kernel

2008-02-05T17:44:28Z

UML was panicing in the case of failures of libc calls which shouldn't happen. This is an overreaction since a failure from libc doesn't normally mean that kernel data structures are in an unknown state. Instead, the current process should just be killed if there is no way to recover. The case that prompted this was a failure of PTRACE_SETREGS restoring the same state that was read by PTRACE_GETREGS. It appears that when a process tries to load a bogus value into a segment register, it segfaults (as expected) and the value is actually loaded and is seen by PTRACE_GETREGS (not expected). This case is fixed by forcing a fatal SIGSEGV on the process so that it immediately dies. fatal_sigsegv was added for this purpose. It was declared as noreturn, so in order to pursuade gcc that it actually does not return, I added a call to os_dump_core (and declared it noreturn) so that I get a core file if somehow the process survives. All other calls in arch/um/os-Linux/skas/process.c got the same treatment, with failures causing the process to die instead of a kernel panic, with some exceptions. userspace_tramp exits with status 1 if anything goes wrong there. That will cause start_userspace to return an error. copy_context_skas0 and map_stub_pages also now return errors instead of panicing. Callers of thes functions were changed to check for errors and do something appropriate. Usually that's to return an error to their callers. check_skas3_ptrace_faultinfo just exits since that's too early to do anything else. save_registers, restore_registers, and init_registers now return status instead of panicing on failure, with their callers doing something appropriate. There were also duplicate declarations of save_registers and restore_registers in os.h - these are gone. I noticed and fixed up some whitespace damage. Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

uml: use ptrace directly in libc code

2008-02-05T17:44:28Z

Some register accessor cleanups - userspace() was calling restore_registers and save_registers for no reason, since userspace() is on the libc side of the house, and these add no value over calling ptrace directly init_thread_registers and get_safe_registers were the same thing, so init_thread_registers is gone Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

uml: floating point signal delivery fixes

2007-10-16T16:43:07Z

Handle floating point state in across signals correctly. UML/i386 needs to know whether the host does PTRACE_[GS]ETFPXREGS, so an arch_init_registers hook is added, which on x86_64 does nothing. UML doesn't save and restore floating point registers on kernel entry and exit, so they need to be copied between the host process and the sigcontext. save_fpx_registers and restore_fpx_registers are added for this purpose. save_fp_registers and restore_fp_registers already exist. There was a bunch of floating point state conversion code in arch/um/sys-i386/ptrace.c which isn't needed there, but is needed in signal.c, so it is moved over. The i386 code now distinguishes between fp and fpx state and handles them correctly. The x86_64 code just needs to copy state as-is between the host process and the stack. There are also some fixes there to pass the correct address of the floating point state around. Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds