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The combination of noexec=on and a clock_gettime call with clock id
CLOCK_THREAD_CPUTIME_ID is broken. The vdso code switches to the
access register mode to get access to the per-cpu data structure to
execute the magic ectg instruction. After the ectg instruction the
code always switches back to the primary mode but for noexec=on the
correct mode is the secondary mode. The effect of the bug is that the
user space program looses the access to all mappings without PROT_EXEC,
e.g. the stack. The problem is fixed by restoring the mode that has
been active before the switch to the access register mode.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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The extract cpu time instruction (ectg) instruction allows the user
process to get the current thread cputime without calling into the
kernel. The code that uses the instruction needs to switch to the
access registers mode to get access to the per-cpu info page that
contains the two base values that are needed to calculate the current
cputime from the CPU timer with the ectg instruction.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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Add a vdso to speed up gettimeofday and clock_getres/clock_gettime for
CLOCK_REALTIME/CLOCK_MONOTONIC.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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