From: Eric W. Biederman ebiederm@xmission.com
commit 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 upstream.
Update save_v86_state to always complete all of it's work except possibly some of the copies to userspace even if save_v86_state takes a fault. This ensures that the kernel is always in a sane state, even if userspace has done something silly.
When save_v86_state takes a fault update it to force userspace to take a SIGSEGV and terminate the userspace application.
As Andy pointed out in review of the first version of this change there are races between sigaction and the application terinating. Now that the code has been modified to always perform all save_v86_state's work (except possibly copying to userspace) those races do not matter from a kernel perspective.
Forcing the userspace application to terminate (by resetting it's handler to SIGDFL) is there to keep everything as close to the current behavior as possible while removing the unique (and difficult to maintain) use of do_exit.
If this new SIGSEGV happens during handle_signal the next time around the exit_to_user_mode_loop, SIGSEGV will be delivered to userspace.
All of the callers of handle_vm86_trap and handle_vm86_fault run the exit_to_user_mode_loop before they return to userspace any signal sent to the current task during their execution will be delivered to the current task before that tasks exits to usermode.
Cc: Andy Lutomirski luto@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: x86@kernel.org Cc: H Peter Anvin hpa@zytor.com v1: https://lkml.kernel.org/r/20211020174406.17889-10-ebiederm@xmission.com Link: https://lkml.kernel.org/r/877de1xcr6.fsf_-_@disp2133 Signed-off-by: Eric W. Biederman ebiederm@xmission.com Cc: Thomas Backlund tmb@iki.fi Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/vm86_32.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/vm86_32.c +++ b/arch/x86/kernel/vm86_32.c @@ -142,6 +142,7 @@ void save_v86_state(struct kernel_vm86_r
user_access_end();
+exit_vm86: preempt_disable(); tsk->thread.sp0 = vm86->saved_sp0; tsk->thread.sysenter_cs = __KERNEL_CS; @@ -161,7 +162,8 @@ Efault_end: user_access_end(); Efault: pr_alert("could not access userspace vm86 info\n"); - do_exit(SIGSEGV); + force_sigsegv(SIGSEGV); + goto exit_vm86; }
static int do_vm86_irq_handling(int subfunction, int irqnumber);