From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC
Date: Mon, 10 Aug 2015 10:47:56 +0100 [thread overview]
Message-ID: <20150810094755.GE1604@arm.com> (raw)
In-Reply-To: <1438992995-22610-3-git-send-email-timur@codeaurora.org>
On Sat, Aug 08, 2015 at 01:16:35AM +0100, Timur Tabi wrote:
> If the DCC driver loads, then disable user-space access to the DCC so that
> we don't have two entities trying to access the DCC at the same time.
>
> Signed-off-by: Timur Tabi <timur@codeaurora•org>
> ---
> arch/arm/include/asm/dcc.h | 15 +++++++++++++++
> arch/arm64/include/asm/dcc.h | 11 +++++++++++
> drivers/tty/hvc/hvc_dcc.c | 2 ++
> 3 files changed, 28 insertions(+)
>
> diff --git a/arch/arm/include/asm/dcc.h b/arch/arm/include/asm/dcc.h
> index b74899d..c50056b 100644
> --- a/arch/arm/include/asm/dcc.h
> +++ b/arch/arm/include/asm/dcc.h
> @@ -9,8 +9,11 @@
> * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> * GNU General Public License for more details.
> */
> +#ifndef __ASM_DCC_H
> +#define __ASM_DCC_H
>
> #include <asm/barrier.h>
> +#include <asm/hardware/cp14.h>
>
> static inline u32 __dcc_getstatus(void)
> {
> @@ -39,3 +42,15 @@ static inline void __dcc_putchar(char c)
> : "r" (c));
> isb();
> }
> +
> +static inline void __dcc_initialize(void)
> +{
> + u32 val;
> +
> + /* Disable user-space access to DCC */
> + val = MRC14(0, c0, c1, 0);
> + val |= 1 << 12; /* DSCR[Comms] */
> + MCR14(val, 0, c0, c1, 0);
> +}
> +
> +#endif
> diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h
> index fcb8d7d..a6496f2 100644
> --- a/arch/arm64/include/asm/dcc.h
> +++ b/arch/arm64/include/asm/dcc.h
> @@ -49,4 +49,15 @@ static inline void __dcc_putchar(char c)
> isb();
> }
>
> +static inline void __dcc_initialize(void)
> +{
> + u32 val;
> +
> + /* Disable user-space access to DCC */
> + asm volatile ("mrs %0, mdscr_el1\n"
> + " orr %0, %0, #4096\n" /* Set the TDCC bit */
So this is the same as your "1 << 12" for arch/arm/. Shouldn't we
#define that someplace common?
> + " msr mdscr_el1, %0\n"
> + : "=r" (val));
> +}
> +
> #endif
> diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
> index 47654ea..e260acb 100644
> --- a/drivers/tty/hvc/hvc_dcc.c
> +++ b/drivers/tty/hvc/hvc_dcc.c
> @@ -76,6 +76,8 @@ static int __init hvc_dcc_console_init(void)
> if (!hvc_dcc_check())
> return -ENODEV;
>
> + __dcc_initialize();
> +
> /* Returns -1 if error */
> ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
Can this driver be built as a module and unloaded? If so, should we
re-enable userspace access when the kernel doesn't need it anymore?
Finally, have you checked the behaviour on CPU hotplug? It looks like we
zero mdscr_el1 in the cold boot path. The alternative is to set this bit
there and never allow userspace access. Do you know of any compelling
use-cases where userspace accesses the DCC directly?
Will
next prev parent reply other threads:[~2015-08-10 9:47 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-08 0:16 [PATCH 1/3] [v2] hvc_dcc: don't ignore errors during initialization Timur Tabi
2015-08-08 0:16 ` [PATCH 2/3] [v4] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc Timur Tabi
2015-08-10 9:40 ` Will Deacon
2015-08-17 23:56 ` Timur Tabi
2015-08-18 8:21 ` Dave Martin
2015-08-18 19:07 ` Timur Tabi
2015-08-19 10:14 ` Dave Martin
2015-08-19 16:16 ` Timur Tabi
2015-08-19 16:37 ` Dave Martin
2015-08-24 23:51 ` sboyd at codeaurora.org
2015-09-02 11:10 ` Dave Martin
2015-08-08 0:16 ` [PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC Timur Tabi
2015-08-10 9:47 ` Will Deacon [this message]
2015-08-17 22:45 ` Timur Tabi
2015-08-10 9:48 ` [PATCH 1/3] [v2] hvc_dcc: don't ignore errors during initialization Will Deacon
2015-08-19 22:51 ` Timur Tabi
-- strict thread matches above, loose matches on Subject: below --
2015-08-19 23:02 [PATCH 1/3] [v3] " Timur Tabi
2015-08-19 23:02 ` [PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC Timur Tabi
2015-08-20 10:46 ` Will Deacon
2015-08-20 13:02 ` Catalin Marinas
2015-08-20 15:22 ` Timur Tabi
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