From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Thomas Garnier <thgarnie@google.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
"David Howells" <dhowells@redhat.com>,
"Dave Hansen" <dave.hansen@intel.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"René Nyffenegger" <mail@renenyffenegger.ch>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kees Cook" <keescook@chromium.org>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
"David S . Miller" <davem@davemloft.net>,
"Andy Lutomirski" <luto@kernel.org>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Nicolas Pitre" <nicolas.pitre@linaro.org>,
"Petr Mladek" <pmladek@suse.com>,
"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
"Sergey Senozhatsky" <sergey.senozhatsky@gmail.com>,
"Helge Deller" <deller@gmx.de>, "Rik van Riel" <riel@redhat.com>,
"Ingo Molnar" <mingo@kernel.org>,
"Oleg Nesterov" <oleg@redhat.com>,
"John Stultz" <john.stultz@linaro.org>,
"Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: [PATCH v2 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state
Date: Thu, 9 Mar 2017 16:26:13 +0000 [thread overview]
Message-ID: <20170309162613.GN21222@n2100.armlinux.org.uk> (raw)
In-Reply-To: <CAJcbSZGCFhUx79=bMkOxDRvbfuHmVBWU02HBgEU9T2s7mTChAw@mail.gmail.com>
On Thu, Mar 09, 2017 at 07:56:49AM -0800, Thomas Garnier wrote:
> On Thu, Mar 9, 2017 at 4:23 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> > We generally stick to lower case for the arm64 assembly macros. If we
> > need this, we should stick to the existing convention.
> >
> >> +/* Similar to set_fs(USER_DS) in verify_pre_usermode_state without a warning. */
> >> +.macro VERIFY_PRE_USERMODE_STATE
> >> + mov x1, #TASK_SIZE_64
> >> + str x1, [tsk, #TSK_TI_ADDR_LIMIT]
> >> +.endm
> >
> > We need arm64's set_fs() to configure UAO, too, so this is much weaker
> > than set_fs(), and will leave __{get,put}_user and
> > __copy_{to,from}_user() able to access kernel memory.
> >
> > We don't currently have an asm helper to clear UAO, and unconditionally
> > poking that on exception return is liable to be somewhat expensive.
> >
> > Also, given we're only trying to catch this in syscalls, I'm afraid I
> > don't see what we gain by doing this in the entry assembly.
> >
>
> I optimized all architectures from the arm (32-bit) discussion. I will
> come back to a simple bl to the verify function. Thanks!
I wouldn't call what you've done on ARM an "optimisation", because my
comment about making the fast path worthless still stands.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
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next prev parent reply other threads:[~2017-03-09 16:26 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-09 1:24 [PATCH v2 1/4] syscalls: Restore address limit after a syscall Thomas Garnier
2017-03-09 1:24 ` [PATCH v2 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state Thomas Garnier
2017-03-09 1:24 ` [PATCH v2 3/4] arm/syscalls: " Thomas Garnier
2017-03-09 1:24 ` [PATCH v2 4/4] arm64/syscalls: " Thomas Garnier
2017-03-09 12:23 ` Mark Rutland
2017-03-09 15:56 ` Thomas Garnier
2017-03-09 16:05 ` Mark Rutland
2017-03-09 16:19 ` Thomas Garnier
2017-03-09 16:26 ` Russell King - ARM Linux [this message]
2017-03-09 16:35 ` Thomas Garnier
2017-03-09 17:05 ` Russell King - ARM Linux
2017-03-09 8:42 ` [PATCH v2 1/4] syscalls: Restore address limit after a syscall Borislav Petkov
2017-03-09 15:48 ` Thomas Garnier
2017-03-09 17:27 ` Andy Lutomirski
2017-03-09 17:41 ` Thomas Garnier
2017-03-09 10:39 ` Sergey Senozhatsky
2017-03-09 12:09 ` Mark Rutland
2017-03-09 13:44 ` Russell King - ARM Linux
2017-03-09 15:21 ` Mark Rutland
2017-03-09 15:54 ` Thomas Garnier
2017-03-09 15:52 ` Thomas Garnier
2017-03-09 12:32 ` Christian Borntraeger
2017-03-09 15:53 ` Thomas Garnier
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