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Restrict the check: SMAP faults are always protection violations, as the

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SDM points out, so make sure we have PGEX_P. This way NULL dereferences -
which are caused by an unmapped VA, and therefore are not protection
violations - don't take this branch, and don't display a misleading
"SMAP" in ddb.

Adding a PGEX_P check, or not, does not essentially change anything from
a security point of view, it's just a matter of what gets displayed when
a fatal fault comes in.

I didn't put PGEX_P until now, because initially when I wrote the SMAP
implementation Qemu did not always receive the fault if the PGEX_P check
was there, while a native i5 would. I'm unable to reproduce this issue
with a recent Qemu, so I assume I did something wrong when testing in the
first place.
This commit is contained in:
maxv 2018-01-10 20:51:11 +00:00
parent 64389df5f7
commit a8a9f7108d
1 changed files with 5 additions and 7 deletions
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12
sys/arch/amd64/amd64/trap.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: trap.c,v 1.109 2017/12/09 00:52:41 christos Exp $ */
/* $NetBSD: trap.c,v 1.110 2018/01/10 20:51:11 maxv Exp $ */
/*
* Copyright (c) 1998, 2000, 2017 The NetBSD Foundation, Inc.
@ -64,7 +64,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.109 2017/12/09 00:52:41 christos Exp $");
__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.110 2018/01/10 20:51:11 maxv Exp $");
#include "opt_ddb.h"
#include "opt_kgdb.h"
@ -562,13 +562,11 @@ trap(struct trapframe *frame)
}
}
if (cr2 < VM_MAXUSER_ADDRESS) {
if ((frame->tf_err & PGEX_P) &&
cr2 < VM_MAXUSER_ADDRESS) {
/* SMAP might have brought us here */
if (onfault_handler(pcb, frame) == NULL) {
panic("prevented %s %p (SMAP)",
(cr2 < PAGE_SIZE
? "null pointer dereference at"
: "access to"),
panic("prevented access to %p (SMAP)",
(void *)cr2);
}
}