From: Jakub Kicinski Date: Mon, 10 Aug 2020 18:21:11 +0000 (-0700) Subject: bitfield.h: don't compile-time validate _val in FIELD_FIT X-Git-Tag: v4.14.194~74 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b4840e848efa4648a551e3d833bfe7cebde344d2;p=people%2Farne_f%2Fkernel.git bitfield.h: don't compile-time validate _val in FIELD_FIT commit 444da3f52407d74c9aa12187ac6b01f76ee47d62 upstream. 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 Fixes: 1697599ee301a ("bitfield.h: add FIELD_FIT() helper") Link: https://lore.kernel.org/kernel-hardening/CAK7LNASvb0UDJ0U5wkYYRzTAdnEs64HjXpEUL7d=V0CXiAXcNw@mail.gmail.com/ Reported-by: Masahiro Yamada Debugged-by: Sami Tolvanen Signed-off-by: Jakub Kicinski Signed-off-by: Nick Desaulniers Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index f2deb71958b2d..a0675db325e01 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -71,7 +71,7 @@ */ #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)); \ })