| Message ID | 20201029160938.154084-1-irogers@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | libbpf hashmap: Fix undefined behavior in hash_bits | expand |
> On Oct 29, 2020, at 9:09 AM, Ian Rogers <irogers@google.com> wrote: > > If bits is 0, the case when the map is empty, then the >> is the size of > the register which is undefined behavior - on x86 it is the same as a > shift by 0. Fix by handling the 0 case explicitly when running with > address sanitizer. > > A variant of this patch was posted previously as: > https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/ > > Signed-off-by: Ian Rogers <irogers@google.com> > --- > tools/lib/bpf/hashmap.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h > index d9b385fe808c..27d0556527d3 100644 > --- a/tools/lib/bpf/hashmap.h > +++ b/tools/lib/bpf/hashmap.h > @@ -12,9 +12,23 @@ > #include <stddef.h> > #include <limits.h> > > +#ifdef __has_feature > +#define HAVE_FEATURE(f) __has_feature(f) > +#else > +#define HAVE_FEATURE(f) 0 > +#endif > + > static inline size_t hash_bits(size_t h, int bits) > { > /* shuffle bits and return requested number of upper bits */ > +#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer) I am not very familiar with these features. Is address sanitizer same as undefined behavior sanitizer (mentioned in previous version)? > + /* > + * If the requested bits == 0 avoid undefined behavior from a > + * greater-than bit width shift right (aka invalid-shift-exponent). > + */ > + if (bits == 0) > + return -1; Shall we return 0 or -1 (0xffffffff) here? Also, we have HASHMAP_MIN_CAP_BITS == 2. Shall we just make sure we never feed bits == 0 into hash_bits()? Thanks, Song > +#endif > #if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__) > /* LP64 case */ > return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits); > -- > 2.29.1.341.ge80a0c044ae-goog >
On Thu, Oct 29, 2020 at 10:45 AM Song Liu <songliubraving@fb.com> wrote: > > > On Oct 29, 2020, at 9:09 AM, Ian Rogers <irogers@google.com> wrote: > > > > If bits is 0, the case when the map is empty, then the >> is the size of > > the register which is undefined behavior - on x86 it is the same as a > > shift by 0. Fix by handling the 0 case explicitly when running with > > address sanitizer. > > > > A variant of this patch was posted previously as: > > https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/ > > > > Signed-off-by: Ian Rogers <irogers@google.com> > > --- > > tools/lib/bpf/hashmap.h | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h > > index d9b385fe808c..27d0556527d3 100644 > > --- a/tools/lib/bpf/hashmap.h > > +++ b/tools/lib/bpf/hashmap.h > > @@ -12,9 +12,23 @@ > > #include <stddef.h> > > #include <limits.h> > > > > +#ifdef __has_feature > > +#define HAVE_FEATURE(f) __has_feature(f) > > +#else > > +#define HAVE_FEATURE(f) 0 > > +#endif > > + > > static inline size_t hash_bits(size_t h, int bits) > > { > > /* shuffle bits and return requested number of upper bits */ > > +#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer) > > I am not very familiar with these features. Is address sanitizer same > as undefined behavior sanitizer (mentioned in previous version)? My preference would be to special case bits == 0 without the feature guards as per the original change, this is the most correct. There is some feature support for detecting ubsan: https://github.com/google/sanitizers/issues/765 In my case I see this with address sanitizer and older versions of clang don't expose ubsan as a feature. > > + /* > > + * If the requested bits == 0 avoid undefined behavior from a > > + * greater-than bit width shift right (aka invalid-shift-exponent). > > + */ > > + if (bits == 0) > > + return -1; > > Shall we return 0 or -1 (0xffffffff) here? The value isn't used and so doesn't matter. -1 seemed less likely to silently succeed. > Also, we have HASHMAP_MIN_CAP_BITS == 2. Shall we just make sure we > never feed bits == 0 into hash_bits()? I think that'd be a different change. I'd be happy to see it. Thanks, Ian > Thanks, > Song > > > > +#endif > > #if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__) > > /* LP64 case */ > > return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits); > > -- > > 2.29.1.341.ge80a0c044ae-goog > > >
On Thu, Oct 29, 2020 at 9:11 AM Ian Rogers <irogers@google.com> wrote: > > If bits is 0, the case when the map is empty, then the >> is the size of > the register which is undefined behavior - on x86 it is the same as a > shift by 0. Fix by handling the 0 case explicitly when running with > address sanitizer. > > A variant of this patch was posted previously as: > https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/ > > Signed-off-by: Ian Rogers <irogers@google.com> > --- > tools/lib/bpf/hashmap.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h > index d9b385fe808c..27d0556527d3 100644 > --- a/tools/lib/bpf/hashmap.h > +++ b/tools/lib/bpf/hashmap.h > @@ -12,9 +12,23 @@ > #include <stddef.h> > #include <limits.h> > > +#ifdef __has_feature > +#define HAVE_FEATURE(f) __has_feature(f) > +#else > +#define HAVE_FEATURE(f) 0 > +#endif > + > static inline size_t hash_bits(size_t h, int bits) > { > /* shuffle bits and return requested number of upper bits */ > +#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer) > + /* > + * If the requested bits == 0 avoid undefined behavior from a > + * greater-than bit width shift right (aka invalid-shift-exponent). > + */ > + if (bits == 0) > + return -1; > +#endif Oh, just too much # magic here :(... If we want to prevent hash_bits() from being called with bits == 0 (despite the result never used), let's just adjust hashmap__for_each_key_entry and hashmap__for_each_key_entry_safe macros: diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h index d9b385fe808c..488e0ef236cb 100644 --- a/tools/lib/bpf/hashmap.h +++ b/tools/lib/bpf/hashmap.h @@ -174,9 +174,9 @@ bool hashmap__find(const struct hashmap *map, const void *key, void **value); * @key: key to iterate entries for */ #define hashmap__for_each_key_entry(map, cur, _key) \ - for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\ - map->cap_bits); \ - map->buckets ? map->buckets[bkt] : NULL; }); \ + for (cur = map->buckets \ + ? map->buckets[hash_bits(map->hash_fn((_key), map->ctx), map->cap_bits)] \ + : NULL; \ cur; \ cur = cur->next) \ if (map->equal_fn(cur->key, (_key), map->ctx)) Either way it's a bit ugly and long, but at least we don't have extra #-driven ugliness. > #if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__) > /* LP64 case */ > return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits); > -- > 2.29.1.341.ge80a0c044ae-goog >
On Thu, Oct 29, 2020 at 1:16 PM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Thu, Oct 29, 2020 at 9:11 AM Ian Rogers <irogers@google.com> wrote: > > > > If bits is 0, the case when the map is empty, then the >> is the size of > > the register which is undefined behavior - on x86 it is the same as a > > shift by 0. Fix by handling the 0 case explicitly when running with > > address sanitizer. > > > > A variant of this patch was posted previously as: > > https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/ > > > > Signed-off-by: Ian Rogers <irogers@google.com> > > --- > > tools/lib/bpf/hashmap.h | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h > > index d9b385fe808c..27d0556527d3 100644 > > --- a/tools/lib/bpf/hashmap.h > > +++ b/tools/lib/bpf/hashmap.h > > @@ -12,9 +12,23 @@ > > #include <stddef.h> > > #include <limits.h> > > > > +#ifdef __has_feature > > +#define HAVE_FEATURE(f) __has_feature(f) > > +#else > > +#define HAVE_FEATURE(f) 0 > > +#endif > > + > > static inline size_t hash_bits(size_t h, int bits) > > { > > /* shuffle bits and return requested number of upper bits */ > > +#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer) > > + /* > > + * If the requested bits == 0 avoid undefined behavior from a > > + * greater-than bit width shift right (aka invalid-shift-exponent). > > + */ > > + if (bits == 0) > > + return -1; > > +#endif > > Oh, just too much # magic here :(... If we want to prevent hash_bits() > from being called with bits == 0 (despite the result never used), > let's just adjust hashmap__for_each_key_entry and > hashmap__for_each_key_entry_safe macros: > > diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h > index d9b385fe808c..488e0ef236cb 100644 > --- a/tools/lib/bpf/hashmap.h > +++ b/tools/lib/bpf/hashmap.h > @@ -174,9 +174,9 @@ bool hashmap__find(const struct hashmap *map, > const void *key, void **value); > * @key: key to iterate entries for > */ > #define hashmap__for_each_key_entry(map, cur, _key) \ > - for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\ > - map->cap_bits); \ > - map->buckets ? map->buckets[bkt] : NULL; }); \ > + for (cur = map->buckets \ > + ? map->buckets[hash_bits(map->hash_fn((_key), > map->ctx), map->cap_bits)] \ > + : NULL; \ > cur; \ > cur = cur->next) \ > if (map->equal_fn(cur->key, (_key), map->ctx)) > > Either way it's a bit ugly and long, but at least we don't have extra > #-driven ugliness. This can work with the following changes in hashmap.c. I'll resend this as a whole patch. Thanks, Ian --- a/tools/lib/bpf/hashmap.c +++ b/tools/lib/bpf/hashmap.c @@ -156,7 +156,7 @@ int hashmap__insert(struct hashmap *map, const void **old_key, void **old_value) { struct hashmap_entry *entry; - size_t h; + size_t h = 0; int err; if (old_key) @@ -164,7 +164,9 @@ int hashmap__insert(struct hashmap *map, if (old_value) *old_value = NULL; - h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits); + if (map->buckets) + h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits); + if (strategy != HASHMAP_APPEND && hashmap_find_entry(map, key, h, NULL, &entry)) { if (old_key) @@ -208,6 +210,9 @@ bool hashmap__find(const struct hashmap struct hashmap_entry *entry; size_t h; + if (!map->buckets) + return false; + h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits); if (!hashmap_find_entry(map, key, h, NULL, &entry)) return false; @@ -223,6 +228,9 @@ bool hashmap__delete(struct hashmap *map struct hashmap_entry **pprev, *entry; size_t h; + if (!map->buckets) + return false; + h = hash_bits(map->hash_fn(key, map->ctx), map->cap_bits); if (!hashmap_find_entry(map, key, h, &pprev, &entry)) return false; > > #if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__) > > /* LP64 case */ > > return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits); > > -- > > 2.29.1.341.ge80a0c044ae-goog > >
diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h index d9b385fe808c..27d0556527d3 100644 --- a/tools/lib/bpf/hashmap.h +++ b/tools/lib/bpf/hashmap.h @@ -12,9 +12,23 @@ #include <stddef.h> #include <limits.h> +#ifdef __has_feature +#define HAVE_FEATURE(f) __has_feature(f) +#else +#define HAVE_FEATURE(f) 0 +#endif + static inline size_t hash_bits(size_t h, int bits) { /* shuffle bits and return requested number of upper bits */ +#if defined(ADDRESS_SANITIZER) || HAVE_FEATURE(address_sanitizer) + /* + * If the requested bits == 0 avoid undefined behavior from a + * greater-than bit width shift right (aka invalid-shift-exponent). + */ + if (bits == 0) + return -1; +#endif #if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__) /* LP64 case */ return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
If bits is 0, the case when the map is empty, then the >> is the size of the register which is undefined behavior - on x86 it is the same as a shift by 0. Fix by handling the 0 case explicitly when running with address sanitizer. A variant of this patch was posted previously as: https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/ Signed-off-by: Ian Rogers <irogers@google.com> --- tools/lib/bpf/hashmap.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+)