From: John Fastabend <john.fastabend@gmail.com>
To: jolsa@kernel.org, andrii.nakryiko@gmail.com, ast@kernel.org,
daniel@iogearbox.net
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, john.fastabend@gmail.com
Subject: [bpf PATCH] bpf: Do not allow btf_ctx_access with __int128 types
Date: Wed, 24 Jun 2020 15:20:39 -0700 [thread overview]
Message-ID: <159303723962.11287.13309537171132420717.stgit@john-Precision-5820-Tower> (raw)
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")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
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 5c1ea99..8b81fbb 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 58c9af1..9a1a98d 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)) {
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)) {
next reply other threads:[~2020-06-24 22:20 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 22:20 John Fastabend [this message]
2020-06-25 15:01 ` [bpf PATCH] bpf: Do not allow btf_ctx_access with __int128 types Daniel Borkmann
-- strict thread matches above, loose matches on Subject: below --
2020-06-23 17:13 [bpf PATCH] bpf: do " John Fastabend
2020-06-23 18:33 ` Andrii Nakryiko
2020-06-24 22:23 ` John Fastabend
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