From: John Fastabend <john.fastabend@gmail.com>
Date: Wed, 24 Jun 2020 15:20:39 -0700
Subject: bpf: Do not allow btf_ctx_access with __int128 types
Patch-mainline: v5.8-rc5
Git-commit: a9b59159d338d414acaa8e2f569d129d51c76452
References: bsc#1155518
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
Acked-by: Gary Lin <glin@suse.com>
NOTE:
This patch omits the part for BPF_MODIFY_RETURN since it's not supported
in SLE15-SP2.
---
include/linux/btf.h | 5 +++++
kernel/bpf/btf.c | 2 +-
2 files changed, 6 insertions(+), 1 deletion(-)
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -64,6 +64,11 @@ static inline bool btf_type_is_int(const
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;
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3677,7 +3677,7 @@ bool btf_ctx_access(int off, int size, e
/* skip modifiers */
while (btf_type_is_modifier(t))
t = btf_type_by_id(btf, t->type);
- if (btf_type_is_int(t))
+ if (btf_type_is_small_int(t))
/* accessing a scalar */
return true;
if (!btf_type_is_ptr(t)) {