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amd64: Avoid enabling interrupts when handling kernel mode prot faults

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When PTI is enabled, we may have been on the trampoline stack when iret
faults.  So, we have to switch back to the regular stack before
re-entering trap().

trap() has the somewhat strange behaviour of re-enabling interrupts when
handling certain kernel-mode execeptions.  In particular, it was doing
this for exceptions raised during execution of iret.  When switching
away from the trampoline stack, however, the thread must not be migrated
to a different CPU.  Fix the problem by simply leaving interrupts
disabled during the window.

Reported by:	syzbot+6cfa544fd86ad4647ffc@syzkaller.appspotmail.com
Reported by:	syzbot+cfdfc9e5a8f28f11a7f5@syzkaller.appspotmail.com
Reviewed by:	kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D30578
This commit is contained in:
Mark Johnston 2021-05-31 18:49:33 -04:00
parent 8790fe3058
commit 4a59cbc125
1 changed files with 23 additions and 15 deletions
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38
sys/amd64/amd64/trap.c
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@ -236,25 +236,31 @@ trap(struct trapframe *frame)
* interrupts disabled until they are accidentally
* enabled later.
*/
if (TRAPF_USERMODE(frame))
if (TRAPF_USERMODE(frame)) {
uprintf(
"pid %ld (%s): trap %d with interrupts disabled\n",
(long)curproc->p_pid, curthread->td_name, type);
else if (type != T_NMI && type != T_BPTFLT &&
type != T_TRCTRAP) {
/*
* XXX not quite right, since this may be for a
* multiple fault in user mode.
*/
printf("kernel trap %d with interrupts disabled\n",
type);
} else {
switch (type) {
case T_NMI:
case T_BPTFLT:
case T_TRCTRAP:
case T_PROTFLT:
case T_SEGNPFLT:
case T_STKFLT:
break;
default:
printf(
"kernel trap %d with interrupts disabled\n",
type);
/*
* We shouldn't enable interrupts while holding a
* spin lock.
*/
if (td->td_md.md_spinlock_count == 0)
enable_intr();
/*
* We shouldn't enable interrupts while holding a
* spin lock.
*/
if (td->td_md.md_spinlock_count == 0)
enable_intr();
}
}
}
@ -444,6 +450,8 @@ trap(struct trapframe *frame)
* Magic '5' is the number of qwords occupied by
* the hardware trap frame.
*/
KASSERT((read_rflags() & PSL_I) == 0,
("interrupts enabled"));
if (frame->tf_rip == (long)doreti_iret) {
frame->tf_rip = (long)doreti_iret_fault;
if ((PCPU_GET(curpmap)->pm_ucr3 !=