diff options
authorJohn Fastabend <john.fastabend@gmail.com>2020-06-24 15:20:39 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2020-06-25 16:17:05 +0200
commita9b59159d338d414acaa8e2f569d129d51c76452 (patch)
parentbpf: Fix formatting in documentation for BPF helpers (diff)
bpf: Do not allow btf_ctx_access with __int128 types
To ensure btf_ctx_access() is safe the verifier checks that the BTF arg type is an int, enum, or pointer. When the function does the BTF arg lookup it uses the calculation 'arg = off / 8' using the fact that registers are 8B. This requires that the first arg is in the first reg, the second in the second, and so on. However, for __int128 the arg will consume two registers by default LLVM implementation. So this will cause the arg layout assumed by the 'arg = off / 8' calculation to be incorrect. Because __int128 is uncommon this patch applies the easiest fix and will force int types to be sizeof(u64) or smaller so that they will fit in a single register. v2: remove unneeded parens per Andrii's feedback Fixes: 9e15db66136a1 ("bpf: Implement accurate raw_tp context access via BTF") Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/159303723962.11287.13309537171132420717.stgit@john-Precision-5820-Tower
2 files changed, 7 insertions, 2 deletions
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 5c1ea99b480f..8b81fbb4497c 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -82,6 +82,11 @@ static inline bool btf_type_is_int(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_INT;
+static inline bool btf_type_is_small_int(const struct btf_type *t)
+ return btf_type_is_int(t) && t->size <= sizeof(u64);
static inline bool btf_type_is_enum(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_ENUM;
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 58c9af1d4808..9a1a98dd9e97 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3746,7 +3746,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
return false;
t = btf_type_skip_modifiers(btf, t->type, NULL);
- if (!btf_type_is_int(t)) {
+ if (!btf_type_is_small_int(t)) {
"ret type %s not allowed for fmod_ret\n",
@@ -3768,7 +3768,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
/* skip modifiers */
while (btf_type_is_modifier(t))
t = btf_type_by_id(btf, t->type);
- if (btf_type_is_int(t) || btf_type_is_enum(t))
+ if (btf_type_is_small_int(t) || btf_type_is_enum(t))
/* accessing a scalar */
return true;
if (!btf_type_is_ptr(t)) {