Re: [PATCH net-next 5/5] bpf: write back the verifier log buffer as it gets filled

On Thu, 05 Oct 2017 23:10:03 +0200, Daniel Borkmann wrote:

quoted

  include/linux/bpf_verifier.h |  7 +++--
  kernel/bpf/verifier.c        | 64 +++++++++++++++++++++++++++++++-------------
  2 files changed, 50 insertions(+), 21 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 598802dd1897..c0f0e210c3f8 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h

@@ -140,10 +140,13 @@ struct bpf_verifier_env {
  	bool seen_direct_write;
  	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */

-	u32 log_level;
+	char __user *log_ubuf;
+	u32 log_usize;
+	u32 log_ulen;
+	char *log_buf;
  	u32 log_size;
  	u32 log_len;
-	char *log_buf;
+	u32 log_level;  

Small request: given we'd now have log_{level,ubuf,usize,ulen,buf,size,len}
in struct bpf_verifier_env, could we abstract that a bit e.g. into something
like struct bpf_verifier_log, which has level and kbuf and ubuf as members
of which {k,u}buf would be something like struct bpf_verifier_buf with three
members (mem or buf, len_total, len_used) or such. I think most of patch 1
is on passing env into verbose, so likely wouldn't be too much change required
for this, but would be nice to make that a bit more structured if we need to
touch it anyway.

I thought about it but got put off by the fact that on of the bufs has
a special __user marking..  So I don't think we can really have a common
struct bpf_verifier_buf for the two :S  Any suggestions on how to work
around that?

quoted

  		ret = -ENOMEM;
-		env->log_buf = vmalloc(env->log_size);
+		env->log_buf = page_address(alloc_page(GFP_USER));  

alloc_page() can return NULL, if I spot this correctly, then page_address()
cannot handle NULL and would try to deref it, no? Am I missing something?

Oh, I need to fix the nfp driver too, then!