On Wed, Nov 17, 2021 at 10:51 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Wed, Nov 17, 2021 at 10:47:13AM -0800, Kyle Huey wrote: > > rr, a userspace record and replay debugger[0], is completely broken on > > 5.16rc1. I bisected this to 00b06da29cf9dc633cdba87acd3f57f4df3fd5c7. > > > > That patch makes two changes, it blocks sigaction from changing signal > > handlers once the kernel has decided to force the program to take a > > signal and it also stops notifying ptracers of the signal in the same > > circumstances. The latter behavior is just wrong. There's no reason > > that ptrace should not be able to observe and even change > > (non-SIGKILL) forced signals. It should be reverted. > > > > This behavior change is also observable in gdb. If you take a program > > that sets SIGSYS to SIG_IGN and then raises a SIGSYS via > > SECCOMP_RET_TRAP and run it under gdb on a good kernel gdb will stop > > when the SIGSYS is raised, let you inspect program state, etc. After > > the SA_IMMUTABLE change gdb won't stop until the program has already > > died of SIGSYS. > > Ah, hm, this was trying to fix the case where a program trips > SECCOMP_RET_KILL (which is a "fatal SIGSYS"), and had been unobservable > before. I guess the fix was too broad... Perhaps I don't understand precisely what you mean by this, but gdb's behavior for a program that is SECCOMP_RET_KILLed was not changed by this patch (the SIGSYS is not observed until after program exit before or after this change). - Kyle
