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ARM: make kuser helpers depend on MMU

PATCH New Nathan Lynch 2 participants 3 messages Nov 3, 2014 – Nov 4, 2014 Arm (32-bit)

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Nathan Lynch

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PATCH 1/1 ARM: make kuser helpers depend on MMU

The kuser helpers page is not set up on non-MMU systems, so it does not make sense to allow CONFIG_KUSER_HELPERS to be enabled when CONFIG_MMU=n. Allowing it to be set on !MMU results in an oops in set_tls (used in execve and the arm_syscall trap handler):

Unhandled exception: IPSR = 00000005 LR = fffffff1

CPU: 0 PID: 1 Comm: swapper Not tainted 3.18.0-rc1-00041-ga30465a #216
task: 8b838000 ti: 8b82a000 task.ti: 8b82a000
PC is at flush_thread+0x32/0x40
LR is at flush_thread+0x21/0x40
pc : [<8f00157a>]    lr : [<8f001569>]    psr: 4100000b

sp : 8b82be20 ip : 00000000 fp : 8b83c000
r10: 00000001 r9 : 88018c84 r8 : 8bb85000
r7 : 8b838000 r6 : 00000000 r5 : 8bb77400 r4 : 8b82a000 r3 : ffff0ff0 r2 : 8b82a000 r1 : 00000000 r0 : 88020354
xPSR: 4100000b

CPU: 0 PID: 1 Comm: swapper Not tainted 3.18.0-rc1-00041-ga30465a #216
[<8f002bc1>] (unwind_backtrace) from [<8f002033>] (show_stack+0xb/0xc)
[<8f002033>] (show_stack) from [<8f00265b>] (__invalid_entry+0x4b/0x4c)

As best I can tell this issue existed for the set_tls ARM syscall before commit fbfb872f5f41 "ARM: 8148/1: flush TLS and thumbee register state during exec" consolidated the TLS manipulation code into the set_tls helper function, but now that we're using it to flush register state during execve, !MMU users encounter the oops at the first exec.

Prevent CONFIG_MMU=n configurations from enabling
CONFIG_KUSER_HELPERS.

Fixes fbfb872f5f41 ARM: 8148/1: flush TLS and thumbee register state during exec
Signed-off-by Nathan Lynch <[email protected]>
Reported-by Stefan Agner <[email protected]>
Cc stable at vger.kernel.org
---
 arch/arm/mm/Kconfig | 1 +
 1 file changed, 1 insertion(+)
arch/arm/mm/Kconfig +1 -0
index ae69809a9e47..7eb94e6fc376 100644
@@ -798,6 +798,7 @@ config NEED_KUSER_HELPERS
 
 config KUSER_HELPERS
 	bool "Enable kuser helpers in vector page" if !NEED_KUSER_HELPERS
+	depends on MMU
 	default y
 	help
 	  Warning: disabling this option may break user programs.
Signature · 1 line
1.9.3
#1 lore raw

PATCH 1/1 ARM: make kuser helpers depend on MMU

Quoted 27 lines · Nathan Lynch

The kuser helpers page is not set up on non-MMU systems, so it does not make sense to allow CONFIG_KUSER_HELPERS to be enabled when CONFIG_MMU=n. Allowing it to be set on !MMU results in an oops in set_tls (used in execve and the arm_syscall trap handler):

Unhandled exception: IPSR = 00000005 LR = fffffff1

CPU: 0 PID: 1 Comm: swapper Not tainted 3.18.0-rc1-00041-ga30465a #216
task: 8b838000 ti: 8b82a000 task.ti: 8b82a000
PC is at flush_thread+0x32/0x40
LR is at flush_thread+0x21/0x40
pc : [<8f00157a>]    lr : [<8f001569>]    psr: 4100000b

sp : 8b82be20 ip : 00000000 fp : 8b83c000
r10: 00000001 r9 : 88018c84 r8 : 8bb85000
r7 : 8b838000 r6 : 00000000 r5 : 8bb77400 r4 : 8b82a000 r3 : ffff0ff0 r2 : 8b82a000 r1 : 00000000 r0 : 88020354
xPSR: 4100000b

CPU: 0 PID: 1 Comm: swapper Not tainted 3.18.0-rc1-00041-ga30465a #216
[<8f002bc1>] (unwind_backtrace) from [<8f002033>] (show_stack+0xb/0xc)
[<8f002033>] (show_stack) from [<8f00265b>] (__invalid_entry+0x4b/0x4c)

As best I can tell this issue existed for the set_tls ARM syscall before commit fbfb872f5f41 "ARM: 8148/1: flush TLS and thumbee register state during exec" consolidated the TLS manipulation code into the set_tls helper function, but now that we're using it to flush register state during execve, !MMU users encounter the oops at the first exec.

Quoted 4 lines

Prevent CONFIG_MMU=n configurations from enabling
CONFIG_KUSER_HELPERS.

Fixes fbfb872f5f41 ARM: 8148/1: flush TLS and thumbee register state during exec

minor nit: Usual syntax here is:

	Fixes: fbfb872f5f41 ("ARM: 8148/1: flush ...")
Quoted 1 line

and it's part of the s-o-b area, so no empty line

Quoted 2 lines
Signed-off-by Nathan Lynch <[email protected]>
Reported-by Stefan Agner <[email protected]>
Acked-by Uwe Kleine-K?nig <[email protected]>

Thanks
Uwe

Signature · 2 lines
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
author
#2 lore raw

PATCH 1/1 ARM: make kuser helpers depend on MMU

Quoted 5 lines · Uwe Kleine-K?nig
Quoted 4 lines · Nathan Lynch

Prevent CONFIG_MMU=n configurations from enabling
CONFIG_KUSER_HELPERS.

Quoted 7 lines
Quoted 1 line
Fixes fbfb872f5f41 ARM: 8148/1: flush TLS and thumbee register state during exec

minor nit: Usual syntax here is:

	Fixes: fbfb872f5f41 ("ARM: 8148/1: flush ...")
Quoted 1 line

and it's part of the s-o-b area, so no empty line

Indeed, will fix before sending to the patch tracker.

Quoted 4 lines
Quoted 3 lines
Signed-off-by Nathan Lynch <[email protected]>
Reported-by Stefan Agner <[email protected]>
Acked-by Uwe Kleine-K?nig <[email protected]>

Thanks.