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[S390] vdso: clock_gettime of CLOCK_THREAD_CPUTIME_ID with noexec=on

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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>
This commit is contained in:
Martin Schwidefsky 2009-07-24 12:39:52 +02:00
parent 3a6ba4600d
commit 1277580fe5
1 changed files with 9 additions and 2 deletions
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11
arch/s390/kernel/vdso64/clock_gettime.S
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@ -88,10 +88,17 @@ __kernel_clock_gettime:
llilh %r4,0x0100
sar %a4,%r4
lghi %r4,0
epsw %r5,0
sacf 512 /* Magic ectg instruction */
.insn ssf,0xc80100000000,__VDSO_ECTG_BASE(4),__VDSO_ECTG_USER(4),4
sacf 0
sar %a4,%r2
tml %r5,0x4000
jo 11f
tml %r5,0x8000
jno 10f
sacf 256
j 11f
10: sacf 0
11: sar %a4,%r2
algr %r1,%r0 /* r1 = cputime as TOD value */
mghi %r1,1000 /* convert to nanoseconds */
srlg %r1,%r1,12 /* r1 = cputime in nanosec */