Messages in this thread | | | Date | Tue, 2 Aug 2022 22:20:04 -0600 | Subject | Re: [PATCH] net: seg6: initialize induction variable to first valid array index | From | David Ahern <> |
| |
[ cc Andrea ]
On 8/2/22 10:12 AM, Nick Desaulniers wrote: > Fixes the following warnings observed when building > CONFIG_IPV6_SEG6_LWTUNNEL=y with clang: > > net/ipv6/seg6_local.o: warning: objtool: seg6_local_fill_encap() falls > through to next function seg6_local_get_encap_size() > net/ipv6/seg6_local.o: warning: objtool: seg6_local_cmp_encap() falls > through to next function input_action_end() > > LLVM can fully unroll loops in seg6_local_get_encap_size() and > seg6_local_cmp_encap(). One issue in those loops is that the induction > variable is initialized to 0. The loop iterates over members of > seg6_action_params, a global array of struct seg6_action_param calling > their put() function pointer members. seg6_action_param uses an array > initializer to initialize SEG6_LOCAL_SRH and later elements, which is > the third enumeration of an anonymous union. > > The guard `if (attrs & SEG6_F_ATTR(i))` may prevent this from being > called at runtime, but it would still be UB for > `seg6_action_params[0]->put` to be called; the unrolled loop will make > the initial iterations unreachable, which LLVM will later rotate to > fallthrough to the next function. > > Make this more obvious that this cannot happen to the compiler by > initializing the loop induction variable to the minimum valid index that > seg6_action_params is initialized to. > > Reported-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > net/ipv6/seg6_local.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c > index 2cd4a8d3b30a..b7de5e46fdd8 100644 > --- a/net/ipv6/seg6_local.c > +++ b/net/ipv6/seg6_local.c > @@ -1614,7 +1614,7 @@ static void __destroy_attrs(unsigned long parsed_attrs, int max_parsed, > * callback. If the callback is not available, then we skip to the next > * attribute; otherwise, we call the destroy() callback. > */ > - for (i = 0; i < max_parsed; ++i) { > + for (i = SEG6_LOCAL_SRH; i < max_parsed; ++i) { > if (!(parsed_attrs & SEG6_F_ATTR(i))) > continue; > > @@ -1643,7 +1643,7 @@ static int parse_nla_optional_attrs(struct nlattr **attrs, > struct seg6_action_param *param; > int err, i; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; ++i) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; ++i) { > if (!(desc->optattrs & SEG6_F_ATTR(i)) || !attrs[i]) > continue; > > @@ -1742,7 +1742,7 @@ static int parse_nla_action(struct nlattr **attrs, struct seg6_local_lwt *slwt) > } > > /* parse the required attributes */ > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (desc->attrs & SEG6_F_ATTR(i)) { > if (!attrs[i]) > return -EINVAL; > @@ -1847,7 +1847,7 @@ static int seg6_local_fill_encap(struct sk_buff *skb, > > attrs = slwt->desc->attrs | slwt->parsed_optattrs; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (attrs & SEG6_F_ATTR(i)) { > param = &seg6_action_params[i]; > err = param->put(skb, slwt); > @@ -1927,7 +1927,7 @@ static int seg6_local_cmp_encap(struct lwtunnel_state *a, > if (attrs_a != attrs_b) > return 1; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (attrs_a & SEG6_F_ATTR(i)) { > param = &seg6_action_params[i]; > if (param->cmp(slwt_a, slwt_b))
| |