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![Jakub Kicinski](/assets/img/avatar_default.png)
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: 1697599ee3
("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>
Signed-off-by: David S. Miller <davem@davemloft.net>
159 lines
4.8 KiB
C
159 lines
4.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
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* Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
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*/
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#ifndef _LINUX_BITFIELD_H
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#define _LINUX_BITFIELD_H
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#include <linux/build_bug.h>
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#include <asm/byteorder.h>
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/*
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* Bitfield access macros
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*
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* FIELD_{GET,PREP} macros take as first parameter shifted mask
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* from which they extract the base mask and shift amount.
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* Mask must be a compilation time constant.
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*
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* Example:
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*
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* #define REG_FIELD_A GENMASK(6, 0)
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* #define REG_FIELD_B BIT(7)
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* #define REG_FIELD_C GENMASK(15, 8)
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* #define REG_FIELD_D GENMASK(31, 16)
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*
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* Get:
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* a = FIELD_GET(REG_FIELD_A, reg);
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* b = FIELD_GET(REG_FIELD_B, reg);
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*
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* Set:
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* reg = FIELD_PREP(REG_FIELD_A, 1) |
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* FIELD_PREP(REG_FIELD_B, 0) |
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* FIELD_PREP(REG_FIELD_C, c) |
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* FIELD_PREP(REG_FIELD_D, 0x40);
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*
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* Modify:
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* reg &= ~REG_FIELD_C;
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* reg |= FIELD_PREP(REG_FIELD_C, c);
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*/
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#define __bf_shf(x) (__builtin_ffsll(x) - 1)
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#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \
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({ \
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BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \
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_pfx "mask is not constant"); \
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BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero"); \
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BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
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~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
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_pfx "value too large for the field"); \
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BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \
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_pfx "type of reg too small for mask"); \
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__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \
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(1ULL << __bf_shf(_mask))); \
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})
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/**
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* FIELD_MAX() - produce the maximum value representable by a field
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* @_mask: shifted mask defining the field's length and position
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*
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* FIELD_MAX() returns the maximum value that can be held in the field
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* specified by @_mask.
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*/
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#define FIELD_MAX(_mask) \
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({ \
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__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: "); \
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(typeof(_mask))((_mask) >> __bf_shf(_mask)); \
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})
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/**
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* FIELD_FIT() - check if value fits in the field
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* @_mask: shifted mask defining the field's length and position
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* @_val: value to test against the field
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*
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* Return: true if @_val can fit inside @_mask, false if @_val is too big.
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*/
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#define FIELD_FIT(_mask, _val) \
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({ \
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__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: "); \
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!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
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})
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/**
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* FIELD_PREP() - prepare a bitfield element
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* @_mask: shifted mask defining the field's length and position
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* @_val: value to put in the field
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*
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* FIELD_PREP() masks and shifts up the value. The result should
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* be combined with other fields of the bitfield using logical OR.
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*/
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#define FIELD_PREP(_mask, _val) \
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({ \
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__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
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((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
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})
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/**
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* FIELD_GET() - extract a bitfield element
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* @_mask: shifted mask defining the field's length and position
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* @_reg: value of entire bitfield
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*
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* FIELD_GET() extracts the field specified by @_mask from the
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* bitfield passed in as @_reg by masking and shifting it down.
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*/
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#define FIELD_GET(_mask, _reg) \
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({ \
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__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \
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(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \
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})
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extern void __compiletime_error("value doesn't fit into mask")
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__field_overflow(void);
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extern void __compiletime_error("bad bitfield mask")
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__bad_mask(void);
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static __always_inline u64 field_multiplier(u64 field)
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{
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if ((field | (field - 1)) & ((field | (field - 1)) + 1))
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__bad_mask();
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return field & -field;
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}
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static __always_inline u64 field_mask(u64 field)
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{
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return field / field_multiplier(field);
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}
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#define field_max(field) ((typeof(field))field_mask(field))
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#define ____MAKE_OP(type,base,to,from) \
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static __always_inline __##type type##_encode_bits(base v, base field) \
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{ \
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if (__builtin_constant_p(v) && (v & ~field_mask(field))) \
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__field_overflow(); \
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return to((v & field_mask(field)) * field_multiplier(field)); \
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} \
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static __always_inline __##type type##_replace_bits(__##type old, \
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base val, base field) \
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{ \
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return (old & ~to(field)) | type##_encode_bits(val, field); \
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} \
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static __always_inline void type##p_replace_bits(__##type *p, \
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base val, base field) \
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{ \
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*p = (*p & ~to(field)) | type##_encode_bits(val, field); \
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} \
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static __always_inline base type##_get_bits(__##type v, base field) \
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{ \
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return (from(v) & field)/field_multiplier(field); \
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}
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#define __MAKE_OP(size) \
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____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \
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____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu) \
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____MAKE_OP(u##size,u##size,,)
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____MAKE_OP(u8,u8,,)
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__MAKE_OP(16)
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__MAKE_OP(32)
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__MAKE_OP(64)
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#undef __MAKE_OP
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#undef ____MAKE_OP
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#endif
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