On Sat, Sep 06, 2014 at 11:42:45AM +0200, Daniel Borkmann wrote:

Introduced in commit 314beb9bcabf ("x86: bpf_jit_comp: secure bpf jit
against spraying attacks") and later on replicated in aa2d2c73c21f
("s390/bpf,jit: address randomize and write protect jit code") for
s390 architecture, write protection for BPF JIT images got added and
a random start address of the JIT code, so that it's not on a page
boundary anymore.

Since both use a very similar allocator for the BPF binary header,
we can consolidate this code into the BPF core as it's mostly JIT
independant anyway.

This will also allow for future archs that support DEBUG_SET_MODULE_RONX
to just reuse instead of reimplementing it.

While reviewing the code, I think on s390, the alignment masking
seems not to be correct in it's current form, that is, we make sure
the first instruction starts at an even address as stated by commit
aa2d2c73c21f but masks the start with '& -2' while 2 byte-alignment
should rather be '& ~1'.

JIT tested on x86_64 and s390x with BPF test suite.

Signed-off-by: Daniel Borkmann <redacted>
Acked-by: Alexei Starovoitov <redacted>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Heiko Carstens <redacted>
Cc: Martin Schwidefsky <redacted>
---
 arch/s390/net/bpf_jit_comp.c | 45 ++++++++-------------------------------
 arch/x86/net/bpf_jit_comp.c  | 50 ++++++++++----------------------------------
 include/linux/filter.h       | 13 ++++++++++++
 kernel/bpf/core.c            | 39 ++++++++++++++++++++++++++++++++++
 4 files changed, 72 insertions(+), 75 deletions(-)

Looks good to me (except for the comment about s390 ;).

Acked-by: Heiko Carstens <redacted>