diff options
author | Josef Bacik <jbacik@fb.com> | 2016-09-28 17:54:32 +0300 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2016-09-29 08:35:35 +0300 |
commit | 484611357c19f9e19ef742ebef4505a07d243cc9 (patch) | |
tree | 34f14c2b2ac71d0bf0a53cab096960e7c91ae87f /include/linux/bpf.h | |
parent | 7836667cec5e02ed2ae3eb09b88047b5b5f2343a (diff) | |
download | linux-484611357c19f9e19ef742ebef4505a07d243cc9.tar.xz |
bpf: allow access into map value arrays
Suppose you have a map array value that is something like this
struct foo {
unsigned iter;
int array[SOME_CONSTANT];
};
You can easily insert this into an array, but you cannot modify the contents of
foo->array[] after the fact. This is because we have no way to verify we won't
go off the end of the array at verification time. This patch provides a start
for this work. We accomplish this by keeping track of a minimum and maximum
value a register could be while we're checking the code. Then at the time we
try to do an access into a MAP_VALUE we verify that the maximum offset into that
region is a valid access into that memory region. So in practice, code such as
this
unsigned index = 0;
if (foo->iter >= SOME_CONSTANT)
foo->iter = index;
else
index = foo->iter++;
foo->array[index] = bar;
would be allowed, as we can verify that index will always be between 0 and
SOME_CONSTANT-1. If you wish to use signed values you'll have to have an extra
check to make sure the index isn't less than 0, or do something like index %=
SOME_CONSTANT.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/bpf.h')
-rw-r--r-- | include/linux/bpf.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 5691fdc83819..c201017b5730 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -139,6 +139,13 @@ enum bpf_reg_type { */ PTR_TO_PACKET, PTR_TO_PACKET_END, /* skb->data + headlen */ + + /* PTR_TO_MAP_VALUE_ADJ is used for doing pointer math inside of a map + * elem value. We only allow this if we can statically verify that + * access from this register are going to fall within the size of the + * map element. + */ + PTR_TO_MAP_VALUE_ADJ, }; struct bpf_prog; |