[S390] vdso: clock_gettime of CLOCK_THREAD_CPUTIME_ID with noexec=on
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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@ -88,10 +88,17 @@ __kernel_clock_gettime:
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llilh %r4,0x0100
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sar %a4,%r4
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lghi %r4,0
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epsw %r5,0
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sacf 512 /* Magic ectg instruction */
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.insn ssf,0xc80100000000,__VDSO_ECTG_BASE(4),__VDSO_ECTG_USER(4),4
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sacf 0
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sar %a4,%r2
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tml %r5,0x4000
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jo 11f
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tml %r5,0x8000
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jno 10f
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sacf 256
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j 11f
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10: sacf 0
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11: sar %a4,%r2
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algr %r1,%r0 /* r1 = cputime as TOD value */
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mghi %r1,1000 /* convert to nanoseconds */
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srlg %r1,%r1,12 /* r1 = cputime in nanosec */
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