Re: [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

Kees Cook
2021-10-21T16:16:07Z

On Wed, Oct 20, 2021 at 12:43:56PM -0500, Eric W. Biederman wrote:
> Instead of pretending to send SIGSEGV by calling do_exit(SIGSEGV)
> call force_sigsegv(SIGSEGV) to force the process to take a SIGSEGV
> and terminate.
>
> Update handle_signal to return immediately when save_v86_state fails
> and kills the process. Returning immediately without doing anything
> except killing the process with SIGSEGV is also what signal_setup_done
> does when setup_rt_frame fails. Plus it is always ok to return
> immediately without delivering a signal to a userspace handler when a
> fatal signal has killed the current process.

Do the tools/testing/selftests/x86 tests all pass after these changes? I
know Andy has a bunch of weird corner cases in there.

Reviewed-by: Kees Cook <keescook@chromium.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>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> arch/x86/kernel/signal.c | 6 +++++-
> arch/x86/kernel/vm86_32.c | 2 +-
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index f4d21e470083..25a230f705c1 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -785,8 +785,12 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
> bool stepping, failed;
> struct fpu *fpu = &current->thread.fpu;
>
> - if (v8086_mode(regs))
> + if (v8086_mode(regs)) {
> save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL);
> + /* Has save_v86_state failed and killed the process? */
> + if (fatal_signal_pending(current))
> + return;
> + }
>
> /* Are we from a system call? */
> if (syscall_get_nr(current, regs) != -1) {
> diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
> index 63486da77272..040fd01be8b3 100644
> --- a/arch/x86/kernel/vm86_32.c
> +++ b/arch/x86/kernel/vm86_32.c
> @@ -159,7 +159,7 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval)
> user_access_end();
> Efault:
> pr_alert("could not access userspace vm86 info\n");
> - do_exit(SIGSEGV);
> + force_sigsegv(SIGSEGV);
> }
>
> static int do_vm86_irq_handling(int subfunction, int irqnumber);
> --
> 2.20.1
>

--
Kees Cook