[PATCH 0/3] two small fixes out of kernel/sys.c

[Bradley Morgan]

Two unrelated things that came out of reading kernel/sys.c line by line.
They are in one series only because they came from the same read, patch 3
stands on its own and can be taken without the other two.

Patches 1 and 2 have to go in that order.  PR_FUTEX_HASH is the only case
in the prctl switch that does not check the args it does not use, arg5
does not even reach futex_hash_prctl().  Patch 2 adds the checks.  Patch 1
goes first because prctl() is variadic, so the two callers under tools/
leave the args they do not pass as whatever those registers hold, and
patch 2 would fail them at random without it.

Patch 3 is compat_sysinfo().  It scales the 64 bit memory values down so
they fit the 32 bit fields, and stops when the unit reaches PAGE_SIZE.
But do_sysinfo() hands it bytes with mem_unit at 1, so on a box with
enough ram it stops far too early and drops the high bits.  16 TiB reads
back as 0 and 17 TiB reads back as 1 TiB.  The loop only runs longer on
the path that was already wrong, nothing that works today changes.

Tested on ppc64.

Bradley Morgan (3):
  tools: pass the unused prctl() args explicitly for PR_FUTEX_HASH
  futex: reject the unused PR_FUTEX_HASH arguments
  compat: make compat_sysinfo() scale far enough to actually fit

 include/linux/futex.h                         |  6 ++--
 kernel/futex/core.c                           |  7 +++--
 kernel/sys.c                                  | 28 +++++++++----------
 tools/perf/bench/futex.c                      |  4 +--
 .../futex/functional/futex_priv_hash.c        |  4 +--
 5 files changed, 26 insertions(+), 23 deletions(-)

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2.53.0