alpha: Align signal pointer on entry to signal handler.

PR kern/59327: user stack pointer is not aligned properly

Author: riastradh

sys/arch/alpha/alpha/compat_16_machdep.c

@@ -1,4 +1,4 @@
-/* $NetBSD: compat_16_machdep.c,v 1.23 2021/10/27 04:14:59 thorpej Exp $ */
+/* $NetBSD: compat_16_machdep.c,v 1.24 2025/04/25 00:59:26 riastradh Exp $ */
 
 /*-
  * Copyright (c) 2003 The NetBSD Foundation, Inc.
@@ -85,7 +85,7 @@
 #include <machine/cpu.h>
 #include <machine/reg.h>
 
-__KERNEL_RCSID(0, "$NetBSD: compat_16_machdep.c,v 1.23 2021/10/27 04:14:59 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: compat_16_machdep.c,v 1.24 2025/04/25 00:59:26 riastradh Exp $");
 
 
 #ifdef DEBUG
@@ -112,8 +112,9 @@ sendsig_sigcontext(const ksiginfo_t *ksi, const sigset_t *mask)
 	sig_t catcher = SIGACTION(p, sig).sa_handler;
 
 	tf = l->l_md.md_tf;
-	fp = getframe(l, sig, &onstack);
-	fp--;
+
+	/* Allocate space for the signal handler context. */
+	fp = getframe(l, sig, &onstack, sizeof(*fp), _Alignof(*fp));
 
 #ifdef DEBUG
 	if ((sigdebug & SDB_KSTACK) && p->p_pid == sigpid)

sys/arch/alpha/alpha/machdep.c

@@ -1,4 +1,4 @@
-/* $NetBSD: machdep.c,v 1.382 2025/03/16 19:27:30 thorpej Exp $ */
+/* $NetBSD: machdep.c,v 1.383 2025/04/25 00:59:26 riastradh Exp $ */
 
 /*-
  * Copyright (c) 1998, 1999, 2000, 2019, 2020 The NetBSD Foundation, Inc.
@@ -69,7 +69,7 @@
 
 #include <sys/cdefs.h>			/* RCS ID & Copyright macro defns */
 
-__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.382 2025/03/16 19:27:30 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.383 2025/04/25 00:59:26 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1477,21 +1477,24 @@ regdump(struct trapframe *framep)
 
 
 void *
-getframe(const struct lwp *l, int sig, int *onstack)
+getframe(const struct lwp *l, int sig, int *onstack, size_t size, size_t align)
 {
-	void *frame;
+	uintptr_t frame;
+
+	KASSERT((align & (align - 1)) == 0);
 
 	/* Do we need to jump onto the signal stack? */
 	*onstack =
 	    (l->l_sigstk.ss_flags & (SS_DISABLE | SS_ONSTACK)) == 0 &&
 	    (SIGACTION(l->l_proc, sig).sa_flags & SA_ONSTACK) != 0;
 
 	if (*onstack)
-		frame = (void *)((char *)l->l_sigstk.ss_sp +
-					l->l_sigstk.ss_size);
+		frame = (uintptr_t)l->l_sigstk.ss_sp + l->l_sigstk.ss_size;
 	else
-		frame = (void *)(alpha_pal_rdusp());
-	return (frame);
+		frame = (uintptr_t)alpha_pal_rdusp();
+	frame -= size;
+	frame &= ~(STACK_ALIGNBYTES | (align - 1));
+	return (void *)frame;
 }
 
 void
@@ -1520,11 +1523,10 @@ sendsig_siginfo(const ksiginfo_t *ksi, const sigset_t *mask)
 	struct trapframe *tf;
 	sig_t catcher = SIGACTION(p, ksi->ksi_signo).sa_handler;
 
-	fp = (struct sigframe_siginfo *)getframe(l,ksi->ksi_signo,&onstack);
 	tf = l->l_md.md_tf;
 
 	/* Allocate space for the signal handler context. */
-	fp--;
+	fp = getframe(l, ksi->ksi_signo, &onstack, sizeof(*fp), _Alignof(*fp));
 
 #ifdef DEBUG
 	if ((sigdebug & SDB_KSTACK) && p->p_pid == sigpid)

sys/arch/alpha/include/frame.h

@@ -1,4 +1,4 @@
-/* $NetBSD: frame.h,v 1.10 2019/03/25 19:24:30 maxv Exp $ */
+/* $NetBSD: frame.h,v 1.11 2025/04/25 00:59:27 riastradh Exp $ */
 
 /*
  * Copyright (c) 1994, 1995 Carnegie-Mellon University.
@@ -112,12 +112,15 @@ struct sigframe_siginfo {
 };
 
 #ifdef _KERNEL
-void *getframe(const struct lwp *, int, int *);
+
+#include <sys/stddef.h>
+void *getframe(const struct lwp *, int, int *, size_t, size_t);
 void buildcontext(struct lwp *, const void *, const void *, const void *);
 void sendsig_siginfo(const ksiginfo_t *, const sigset_t *);
 #if defined(COMPAT_16)
 void sendsig_sigcontext(const ksiginfo_t *, const sigset_t *);
 #endif
+
 #endif
 
 #endif /* _ALPHA_FRAME_H_ */

tests/kernel/t_signal_and_sp.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: t_signal_and_sp.c,v 1.15 2025/04/25 00:26:59 riastradh Exp $	*/
+/*	$NetBSD: t_signal_and_sp.c,v 1.16 2025/04/25 00:59:27 riastradh Exp $	*/
 
 /*
  * Copyright (c) 2024 The NetBSD Foundation, Inc.
@@ -27,7 +27,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: t_signal_and_sp.c,v 1.15 2025/04/25 00:26:59 riastradh Exp $");
+__RCSID("$NetBSD: t_signal_and_sp.c,v 1.16 2025/04/25 00:59:27 riastradh Exp $");
 
 #include <sys/wait.h>
 
@@ -426,11 +426,6 @@ ATF_TC_BODY(signalsp_sigaltstack, tc)
 	fprintf(stderr, "stack @ [%p, %p)\n",
 	    stack, stack + SIGSTKSZ + STACK_ALIGNBYTES);
 
-#if defined __alpha__
-	atf_tc_expect_fail("PR kern/59327:"
-	    " user stack pointer is not aligned properly");
-#endif
-
 	/*
 	 * Try with all alignments of high addresses.
 	 */
@@ -578,12 +573,6 @@ ATF_TC_BODY(misaligned_sp_and_signal, tc)
 	sa.sa_handler = &signalsphandler;
 	RL(sigaction(SIGALRM, &sa, NULL));
 
-#if defined __alpha__
-	atf_tc_expect_fail("PR kern/58149:"
-	    " Cannot return from a signal handler"
-	    " if SP was misaligned when the signal arrived");
-#endif
-
 	/*
 	 * Set up an interval timer so that we receive SIGALRM after 50 ms.
 	 */