From: Nick Desaulniers <ndesaulniers@google.com>
To: "David S . Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>,
stable@vger.kernel.org, Masahiro Yamada <masahiroy@kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>, Alex Elder <elder@linaro.org>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
bpf@vger.kernel.org
Subject: [PATCH] bitfield.h: don't compile-time validate _val in FIELD_FIT
Date: Tue, 7 Jul 2020 14:16:41 -0700 [thread overview]
Message-ID: <20200707211642.1106946-1-ndesaulniers@google.com> (raw)
From: Jakub Kicinski <kuba@kernel.org>
When ur_load_imm_any() is inlined into jeq_imm(), it's possible for the
compiler to deduce a case where _val can only have the value of -1 at
compile time. Specifically,
/* struct bpf_insn: _s32 imm */
u64 imm = insn->imm; /* sign extend */
if (imm >> 32) { /* non-zero only if insn->imm is negative */
/* inlined from ur_load_imm_any */
u32 __imm = imm >> 32; /* therefore, always 0xffffffff */
if (__builtin_constant_p(__imm) && __imm > 255)
compiletime_assert_XXX()
This can result in tripping a BUILD_BUG_ON() in __BF_FIELD_CHECK() that
checks that a given value is representable in one byte (interpreted as
unsigned).
FIELD_FIT() should return true or false at runtime for whether a value
can fit for not. Don't break the build over a value that's too large for
the mask. We'd prefer to keep the inlining and compiler optimizations
though we know this case will always return false.
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/kernel-hardening/CAK7LNASvb0UDJ0U5wkYYRzTAdnEs64HjXpEUL7d=V0CXiAXcNw@mail.gmail.com/
Reported-by: Masahiro Yamada <masahiroy@kernel.org>
Debugged-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
include/linux/bitfield.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 48ea093ff04c..4e035aca6f7e 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -77,7 +77,7 @@
*/
#define FIELD_FIT(_mask, _val) \
({ \
- __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: "); \
+ __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: "); \
!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
})
--
2.27.0.383.g050319c2ae-goog
next reply other threads:[~2020-07-07 21:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 21:16 Nick Desaulniers [this message]
2020-07-07 21:49 ` [PATCH] bitfield.h: don't compile-time validate _val in FIELD_FIT Sami Tolvanen
2020-07-07 22:43 ` Alex Elder
2020-07-08 17:10 ` Nick Desaulniers
2020-07-08 17:34 ` Alex Elder
2020-07-08 17:56 ` Nick Desaulniers
2020-07-08 20:34 ` Jakub Kicinski
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