Date: Mon, 7 Jun 2021 01:03:12 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 10e697949ada - stable/13 - amd64: Avoid enabling interrupts when handling kernel mode prot faults Message-ID: <202106070103.15713Cgt099096@gitrepo.freebsd.org>
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The branch stable/13 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=10e697949adaf82070c67f375712b73c099e2017 commit 10e697949adaf82070c67f375712b73c099e2017 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2021-05-31 22:49:33 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2021-06-07 01:02:27 +0000 amd64: Avoid enabling interrupts when handling kernel mode prot faults 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 Sponsored by: The FreeBSD Foundation (cherry picked from commit 4a59cbc1253266ea70d6fa43b1a7c77cc33ec6cd) --- sys/amd64/amd64/trap.c | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-) diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c index 4ce31ce47a45..cc0b8fcf6c17 100644 --- a/sys/amd64/amd64/trap.c +++ b/sys/amd64/amd64/trap.c @@ -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); - - /* - * We shouldn't enable interrupts while holding a - * spin lock. - */ - if (td->td_md.md_spinlock_count == 0) - enable_intr(); + } 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(); + } } } @@ -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 !=
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