Fix the ABI change of the signal delivered on the access to the page

with insufficient protection mode.

For the i386 and amd64, create the tunable, machdep.prot_fault_translation,
with the following behaviour:
	0 = autodetect the signal to be delivered on KERN_PROTECTION_FAILURE
	    from vm_fault based on the ELF OSABI note:
		no note or __FreeBSD_version < 700004 - SIGBUS/BUS_PAGE_FAULT
		note, and __FreeBSD_version >= 700004 - SIGSEGV/SEGV_ACCERR
	1 = always SIGBUS/BUS_PAGE_FAULT
	2 = always SIGSEGV/SEGV_ACCERR

This would do mostly automatic correction of ABI breakage, with the exception
of the untaged binaries for 7-CURRENT/RELENG_7 before the note is fixed. For
them, sysctl would allow to run the binary with manual settings.

Discussed with:	portmgr (kris)
PR:		kern/118304
MFC after:	3 days

2 files changed, 58 insertions, 4 deletions

diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
index 2ce8ed4..7e95cbc 100644
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -144,6 +144,9 @@ SYSCTL_INT(_machdep, OID_AUTO, kdb_on_nmi, CTLFLAG_RW,
 static int panic_on_nmi = 1;
 SYSCTL_INT(_machdep, OID_AUTO, panic_on_nmi, CTLFLAG_RW,
 	&panic_on_nmi, 0, "Panic on NMI");
+static int prot_fault_translation = 0;
+SYSCTL_INT(_machdep, OID_AUTO, prot_fault_translation, CTLFLAG_RW,
+	&prot_fault_translation, 0, "Select signal to deliver on protection fault");
 
 extern char *syscallnames[];
 
@@ -312,8 +315,32 @@ trap(struct trapframe *frame)
 			if (i == SIGSEGV)
 				ucode = SEGV_MAPERR;
 			else {
-				i = SIGSEGV; /* XXX hack */
-				ucode = SEGV_ACCERR;
+				if (prot_fault_translation == 0) {
+					/*
+					 * Autodetect.
+					 * This check also covers the images
+					 * without the ABI-tag ELF note.
+					 */
+					if (p->p_osrel >= 700004) {
+						i = SIGSEGV;
+						ucode = SEGV_ACCERR;
+					} else {
+						i = SIGBUS;
+						ucode = BUS_PAGE_FAULT;
+					}
+				} else if (prot_fault_translation == 1) {
+					/*
+					 * Always compat mode.
+					 */
+					i = SIGBUS;
+					ucode = BUS_PAGE_FAULT;
+				} else {
+					/*
+					 * Always SIGSEGV mode.
+					 */
+					i = SIGSEGV;
+					ucode = SEGV_ACCERR;
+				}
 			}
 			break;
 
diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index 637dedb..ebec7ab 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -158,6 +158,9 @@ SYSCTL_INT(_machdep, OID_AUTO, kdb_on_nmi, CTLFLAG_RW,
 static int panic_on_nmi = 1;
 SYSCTL_INT(_machdep, OID_AUTO, panic_on_nmi, CTLFLAG_RW,
 	&panic_on_nmi, 0, "Panic on NMI");
+static int prot_fault_translation = 0;
+SYSCTL_INT(_machdep, OID_AUTO, prot_fault_translation, CTLFLAG_RW,
+	&prot_fault_translation, 0, "Select signal to deliver on protection fault");
 
 extern char *syscallnames[];
 
@@ -375,8 +378,32 @@ trap(struct trapframe *frame)
 			if (i == SIGSEGV)
 				ucode = SEGV_MAPERR;
 			else {
-				i = SIGSEGV; /* XXX hack */
-				ucode = SEGV_ACCERR;
+				if (prot_fault_translation == 0) {
+					/*
+					 * Autodetect.
+					 * This check also covers the images
+					 * without the ABI-tag ELF note.
+					 */
+					if (p->p_osrel >= 700004) {
+						i = SIGSEGV;
+						ucode = SEGV_ACCERR;
+					} else {
+						i = SIGBUS;
+						ucode = BUS_PAGE_FAULT;
+					}
+				} else if (prot_fault_translation == 1) {
+					/*
+					 * Always compat mode.
+					 */
+					i = SIGBUS;
+					ucode = BUS_PAGE_FAULT;
+				} else {
+					/*
+					 * Always SIGSEGV mode.
+					 */
+					i = SIGSEGV;
+					ucode = SEGV_ACCERR;
+				}
 			}
 			addr = eva;
 			break;