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: 953d2350a30a0 ("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

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 5c1ea99b480fa7164766454be9871b7d247d0d40..8b81fbb4497cf156bb977043a84190e0a3ef1690 100644 (file)
--- 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 58c9af1d480820332a332685790027cdc99fcc52..9a1a98dd9e97c7c9576ec78513e6ced95f7bb4ae 100644 (file)
--- 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)) {
                                bpf_log(log,
                                        "ret type %s not allowed for fmod_ret\n",
                                        btf_kind_str[BTF_INFO_KIND(t->info)]);
@@ -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)) {