s390: always save and restore all registers on context switch

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commit fbbd7f1a51 upstream.

The switch_to() macro has an optimization to avoid saving and
restoring register contents that aren't needed for kernel threads.

There is however the possibility that a kernel thread execve's a user
space program. In such a case the execve'd process can partially see
the contents of the previous process, which shouldn't be allowed.

To avoid this, simply always save and restore register contents on
context switch.

Fixes: fdb6d070ef ("switch_to: dont restore/save access & fpu regs for kernel threads")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Heiko Carstens 2017-11-20 12:38:44 +01:00 • committed by Greg Kroah-Hartman

parent b68df97ec8

commit cb90fcfcdd

1 changed files with 13 additions and 14 deletions

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arch/s390/include/asm/switch_to.h

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