From: John Fastabend john.fastabend@gmail.com
[ Upstream commit a9b59159d338d414acaa8e2f569d129d51c76452 ]
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@jo... Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/btf.h | 5 +++++ kernel/bpf/btf.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h index 5c1ea99b480fa..8b81fbb4497cf 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 d65c6912bdaf6..d1f5d428c9fe2 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3744,7 +3744,7 @@ 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)]); @@ -3766,7 +3766,7 @@ 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)) {