Date: Thu, 8 Sep 2022 19:00:09 +0200 From: =?UTF-8?B?VMSzbA==?= Coosemans <tijl@FreeBSD.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: pho@freebsd.org, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 95f773e59482 - main - i386 copyout_fast: improve detection of a fault on accessing userspace Message-ID: <20220908190009.6377b71a@FreeBSD.org> In-Reply-To: <20220908144909.7e6a0d6b@FreeBSD.org> References: <202208241925.27OJP9Fh069091@gitrepo.freebsd.org> <20220906171826.1629cfcf@FreeBSD.org> <YxdneZXqyaAPmVL0@kib.kiev.ua> <20220906231745.1a0f3c15@FreeBSD.org> <20220907183804.29829b14@FreeBSD.org> <Yxj8mG/lQNIH3fSC@kib.kiev.ua> <20220908144909.7e6a0d6b@FreeBSD.org>
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On Thu, 8 Sep 2022 14:49:09 +0200 T=C4=B3l Coosemans <tijl@FreeBSD.org> wro= te: > On Wed, 7 Sep 2022 23:18:32 +0300 Konstantin Belousov > <kostikbel@gmail.com> wrote: > > On Wed, Sep 07, 2022 at 06:38:04PM +0200, T=C4=B3l Coosemans wrote: =20 > >> So interrupts must have been reenabled somehow, probably by the page > >> fault handler, and this allows context switches and then another proce= ss > >> can call copyout or copyin and corrupt the trampoline stack and > >> copyout_buf. =20 > > I do not see where the interrupts could be reenabled in copyout_fast pa= th, > > without or with page fault on the userspace access. =20 >=20 > The problem is not with userspace page faults. Those are treated > specially by the page fault handler in exception.s causing copyout_fast > and copyin_fast to return immediately with EFAULT so copyout and copyin > fall back to doing a slow copy. >=20 > The problem is with page faults on the kernel space accesses. Before > this commit they were also treated specially, and now they are not. Now= =20 > the page fault handler in exception.s calls trap() which calls > trap_pfault() etc. And trap() contains this: if (trap_enable_intr(type) && td->td_md.md_spinlock_count =3D=3D 0 && frame->tf_eip !=3D (int)cpu_switch_load_gs) enable_intr(); Where trap_enable_intr(T_PAGEFLT) returns true and enable_intr() is sti.
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