From: Catalin Marinas <catalin.marinas@arm.com>
To: Julien Thierry <julien.thierry@arm.com>
Cc: peterz@infradead.org, will.deacon@arm.com,
linux-kernel@vger.kernel.org, mingo@redhat.com,
james.morse@arm.com, hpa@zytor.com,
linux-arm-kernel@lists.infradead.org,
Suzuki K Poulose <Suzuki.Poulose@arm.com>
Subject: Re: [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors
Date: Mon, 10 Dec 2018 14:59:31 +0000 [thread overview]
Message-ID: <20181210145931.GE4048@arrakis.emea.arm.com> (raw)
In-Reply-To: <6424e0f6-7755-c19a-5bc4-a70be5839644@arm.com>
On Fri, Dec 07, 2018 at 08:38:11AM +0000, Julien Thierry wrote:
>
>
> On 12/06/2018 06:25 PM, Catalin Marinas wrote:
> > On Mon, Dec 03, 2018 at 01:55:18PM +0000, Julien Thierry wrote:
> > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > > index 07c3408..cabfcae 100644
> > > --- a/arch/arm64/include/asm/uaccess.h
> > > +++ b/arch/arm64/include/asm/uaccess.h
> > > @@ -233,6 +233,23 @@ static inline void uaccess_enable_not_uao(void)
> > > __uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
> > > }
> > > +#define unsafe_user_region_active uaccess_region_active
> > > +static inline bool uaccess_region_active(void)
> > > +{
> > > + if (system_uses_ttbr0_pan()) {
> > > + u64 ttbr;
> > > +
> > > + ttbr = read_sysreg(ttbr1_el1);
> > > + return ttbr & TTBR_ASID_MASK;
> >
> > Nitpick: could write this in 1-2 lines.
>
> True, I can do that in 1 line.
>
> > > + } else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO)) {
> > > + return (read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN) ?
> > > + false :
> > > + !read_sysreg_s(SYS_PSTATE_PAN);
> > > + }
> >
> > ARM64_ALT_PAN_NOT_UAO implies ARM64_HAS_PAN which implies SCTLR_EL1.SPAN
> > is 0 at run-time. Is this to cope with the case of being called prior to
> > cpu_enable_pan()?
> >
>
> Yes, the issue I can into is that for cpufeatures, .cpu_enable() callbacks
> are called inside stop_machine() which obviously might_sleep and so attempts
> to check whether user_access is on. But for features that get enabled before
> PAN, the PAN bit will be set.
OK, so the PSTATE.PAN bit only makes sense when SCTLR_EL1.SPAN is 0, IOW
the PAN hardware feature has been enabled. Maybe you could write it
(together with some comment):
} else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO) &&
!(read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN)) {
/* only if PAN is present and enabled */
return !read_sysreg_s(SYS_PSTATE_PAN)
}
On the cpufeature.c side of things, it seems that we enable the
static_branch before calling the cpu_enable. I wonder whether changing
the order here would help with avoid the SCTLR_EL1 read (not sure what
else it would break; cc'ing Suzuki).
--
Catalin
next prev parent reply other threads:[~2018-12-10 14:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 13:55 [PATCH v2 0/2] uaccess: Add unsafe accessors for arm64 Julien Thierry
2018-12-03 13:55 ` [RFC PATCH v2 1/2] uaccess: Check no rescheduling function is called in unsafe region Julien Thierry
2019-01-14 12:03 ` Valentin Schneider
2019-01-15 11:48 ` Julien Thierry
2018-12-03 13:55 ` [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors Julien Thierry
2018-12-06 18:25 ` Catalin Marinas
2018-12-07 8:38 ` Julien Thierry
2018-12-10 14:59 ` Catalin Marinas [this message]
2018-12-12 17:40 ` Suzuki K Poulose
2018-12-21 14:57 ` James Morse
2018-12-21 14:57 ` James Morse
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