Patch "x86: bpf_jit: fix compilation of large bpf programs" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

x86: bpf_jit: fix compilation of large bpf programs

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-bpf_jit-fix-compilation-of-large-bpf-programs.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexei Starovoitov <[email protected]>
Date: Fri, 22 May 2015 15:42:55 -0700
Subject: x86: bpf_jit: fix compilation of large bpf programs

From: Alexei Starovoitov <[email protected]>

commit 3f7352bf21f8fd7ba3e2fcef9488756f188e12be upstream.

x86 has variable length encoding. x86 JIT compiler is trying to pick the shortest encoding for given bpf instruction. While doing so the jump targets are changing, so JIT is doing multiple passes over the program. Typical program needs 3 passes. Some very short programs converge with 2 passes. Large programs may need 4 or 5. But specially crafted bpf programs may hit the pass limit and if the program converges on the last iteration the JIT compiler will be producing an image full of 'int 3' insns. Fix this corner case by doing final iteration over bpf program.

---
 arch/x86/net/bpf_jit_comp.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -176,7 +176,12 @@ void bpf_jit_compile(struct sk_filter *f
 	}
 	cleanup_addr = proglen; /* epilogue address */
 
-	for (pass = 0; pass < 10; pass++) {
+	/* JITed image shrinks with every pass and the loop iterates
+	 * until the image stops shrinking. Very large bpf programs
+	 * may converge on the last pass. In such case do one more
+	 * pass to emit the final image
+	 */
+	for (pass = 0; pass < 10 || image; pass++) {
 		u8 seen_or_pass0 = (pass == 0) ? (SEEN_XREG | SEEN_DATAREF | SEEN_MEM) : seen;
 		/* no prologue/epilogue for trivial filters (RET something) */
 		proglen = 0;

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/x86-bpf_jit-fix-compilation-of-large-bpf-programs.patch