| Message ID | 20200810182112.2221964-1-ndesaulniers@google.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2,net] bitfield.h: don't compile-time validate _val in FIELD_FIT | expand |
From: Nick Desaulniers <ndesaulniers@google.com> Date: Mon, 10 Aug 2020 11:21:11 -0700 > 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 > Fixes: 1697599ee301a ("bitfield.h: add FIELD_FIT() helper") > 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> > --- > Changes V1->V2: > * add Fixes tag. Applied, thank you.
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)); \ })