[PATCH v5 0/5] x86: two-phase syscall tracing and seccomp fastpath

Andy Lutomirski luto at amacapital.net
Fri Sep 5 15:13:51 PDT 2014

This applies to:
git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git seccomp-fastpath


This is both a cleanup and a speedup.  It reduces overhead due to
installing a trivial seccomp filter by 87%.  The speedup comes from
avoiding the full syscall tracing mechanism for filters that don't

This series depends on splitting the seccomp hooks into two phases.
The first phase evaluates the filter; it can skip syscalls, allow
them, kill the calling task, or pass a u32 to the second phase.  The
second phase requires a full tracing context, and it sends ptrace
events if necessary.  The seccomp core part is in Kees' seccomp/fastpath

These patches implement a similar split for the x86 syscall
entry work.  The C callback is invoked in two phases: the first has
only a partial frame, and it can request phase 2 processing with a
full frame.

Finally, I switch the 64-bit system_call code to use the new split
entry work.  This is a net deletion of assembly code: it replaces
all of the audit entry muck.

In the process, I fixed some bugs.

If this is acceptable, someone can do the same tweak for the
ia32entry and entry_32 code.

This passes all seccomp tests that I know of.

Changes from v4:
 - Rebased (which seems to have been a no-op)
 - Fixed embarrassing bug that broke allnoconfig
   (patch 3 was missing an ifdef).

Changes from v3:
 - Dropped the core seccomp changes from the email -- Kees has applied them.
 - Add patch 2 (the TIF_NOHZ change).
 - Fix TIF_NOHZ in the two-phase entry code (thanks, Oleg).

Changes from v2:
 - Fixed 32-bit x86 build (and the tests pass).
 - Put the doc patch where it belongs.

Changes from v1:
 - Rebased on top of Kees' shiny new seccomp tree (no effect on the x86
 - Improved patch 6 vs patch 7 split (thanks Alexei!)
 - Fixed bogus -ENOSYS in patch 5 (thanks Kees!)
 - Improved changelog message in patch 6.

Changes from RFC version:
 - The first three patches are more or less the same
 - The rest is more or less a rewrite

Andy Lutomirski (5):
  x86,x32,audit: Fix x32's AUDIT_ARCH wrt audit
  x86,entry: Only call user_exit if TIF_NOHZ
  x86: Split syscall_trace_enter into two phases
  x86_64,entry: Treat regs->ax the same in fastpath and slowpath
  x86_64,entry: Use split-phase syscall_trace_enter for 64-bit syscalls

 arch/x86/include/asm/calling.h |   6 +-
 arch/x86/include/asm/ptrace.h  |   5 ++
 arch/x86/kernel/entry_64.S     |  51 +++++--------
 arch/x86/kernel/ptrace.c       | 165 +++++++++++++++++++++++++++++++++--------
 4 files changed, 164 insertions(+), 63 deletions(-)


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