Kees Cook <keescook@xxxxxxxxxxxx> writes: > On Wed, Oct 20, 2021 at 12:44:01PM -0500, Eric W. Biederman wrote: >> The function try_to_clear_window_buffer is only called from >> rtrap_32.c. After it is called the signal pending state is retested, > > nit: rtrap_32.S > >> and signals are handled if TIF_SIGPENDING is set. This allows >> try_to_clear_window_buffer to call force_fatal_signal and then rely on >> the signal being delivered to kill the process, without any danger of >> returning to userspace, or otherwise using possible corrupt state on >> failure. > > The TIF_SIGPENDING test happens in do_notify_resume(), though I see > other code before that: > > ... > call try_to_clear_window_buffer > add %sp, STACKFRAME_SZ, %o0 > > b signal_p > ... > signal_p: > andcc %g2, _TIF_DO_NOTIFY_RESUME_MASK, %g0 > bz,a ret_trap_continue > ld [%sp + STACKFRAME_SZ + PT_PSR], %t_psr > > mov %g2, %o2 > mov %l6, %o1 > call do_notify_resume > > Will the ret_trap_continue always be skipped? The ret_trap_continue is the break out of the loop. So unless the code is not properly setting the signal to be pending the code should be good. > Also I see the "tp->w_saved = 0" never happens due to the "return" in > try_to_clear_window_buffer. Is that okay? It should be. As you point out the w_saved value is only used in generating signal frames. The code in get_signal should never return and should call do_group_exit which calls do_exit, so building signal frames that happens after get_signal returns should never be reached. Further this is the same way the code makes it to do_exit today. Also looking at it I think the logic is that w_saved == 0 says that the register windows have been saved on the user mode stack, and that clearly has not happened so I think it would in general be a bug to clear w_saved on failure. > Only synchronize_user_stack() > uses it, and that could be called in do_sigreturn(). Should the "return" > be removed? Of course I could be wrong, if David or someone else who knows sparc32 better than me wants to set me straight I would really appreciate it. Eric
