Messages in this thread | | | Date | Fri, 05 Sep 2014 19:10:08 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH] bpf: fix a false positive kmemcheck warning |
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On 09/05/2014 07:00 PM, Hannes Frederic Sowa wrote: > On Fr, 2014-09-05 at 18:20 +0200, Daniel Borkmann wrote: >> Hi Mikulas, >> >> On 09/05/2014 06:01 PM, Mikulas Patocka wrote: >>> This patch fixes false positive kmemcheck warning in bpf. >>> >>> When we try to write the variable len, the compiler generates a code that >>> reads the 32-bit word, modifies the bits belonging to "len" and writes the >>> 32-bit word back. The reading of the word results in kmemcheck warning due >>> to reading uninitialized memory. This patch fixes it by avoiding using bit >>> fields when kmemcheck is enabled. >>> >>> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> >> >> You need to submit this patch to netdev (Cc'ed). >> >>> --- >>> include/linux/filter.h | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> Index: linux-2.6/include/linux/filter.h >>> =================================================================== >>> --- linux-2.6.orig/include/linux/filter.h 2014-09-04 23:04:26.000000000 +0200 >>> +++ linux-2.6/include/linux/filter.h 2014-09-04 23:43:05.000000000 +0200 >>> @@ -325,8 +325,13 @@ struct sock; >>> struct seccomp_data; >>> >>> struct bpf_prog { >>> +#ifdef CONFIG_KMEMCHECK >>> + bool jited; >>> + u32 len; >>> +#else >>> u32 jited:1, /* Is our filter JIT'ed? */ >>> len:31; /* Number of filter blocks */ >>> +#endif >>> struct sock_fprog_kern *orig_prog; /* Original BPF program */ >>> unsigned int (*bpf_func)(const struct sk_buff *skb, >>> const struct bpf_insn *filter); >> >> I don't really like this if-def. If you really want to fix it, can't >> you just use : >> >> kmemcheck_bitfield_begin(bpf_anc_data) >> ... >> kmemcheck_bitfield_end(bpf_anc_data) > > you also need to annotate the bitfield after allocation: > struct bpf_prog *prog = kalloc(...); > kmemcheck_annotate_bitfield(prog, bpf_anc_data);
Yes, sure, sorry if that was not clear from my side, that was what I intended to say with kmemcheck /infrastructure/. :)
> Bye, > Hannes
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