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Marco Elver
0fc1bd38a1
When using CONFIG_KMALLOC_PARTITION_RANDOM, _RET_IP_ was previously used
to identify the allocation site. _RET_IP_, however, evaluates to the
caller's parent's instruction pointer rather than the actual allocation
site; this would lead to collisions where a function performs multiple
allocations.
With the generalization to kmalloc_token_t, we now generate the token at
the outermost macro, and using _THIS_IP_ would fix this for all cases.
Unfortunately, the generic implementation of _THIS_IP_ relies on taking
the address of a local label, which is considered broken by both GCC [1]
and Clang [2] because label addresses are only expected to be used with
computed gotos. While the generic version more or less works today, it
is known to be brittle. For example, Clang -O2 always returns 1 when
this function is inlined:
static inline unsigned long get_ip(void)
{ return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
To provide a reliable unique identifier without breaking architectures
relying on the generic _THIS_IP_, introduce _CODE_LOCATION_: it resolves
to _THIS_IP_ where architectures provide a safe implementation, and
falls back to a zero-cost static marker where _THIS_IP_ is broken.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
Link: https://github.com/llvm/llvm-project/issues/138272 [2]
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260511200136.3201646-2-elver@google.com
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
38 lines
1.3 KiB
C
38 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_INSTRUCTION_POINTER_H
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#define _LINUX_INSTRUCTION_POINTER_H
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#include <asm/linkage.h>
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#define _RET_IP_ (unsigned long)__builtin_return_address(0)
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#ifndef _THIS_IP_
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#define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
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/*
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* The current generic definition of _THIS_IP_ is considered broken by GCC [1]
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* and Clang [2]. In particular, the address of a label is only expected to be
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* used with a computed goto.
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*
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* [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071
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* [2] https://github.com/llvm/llvm-project/issues/138272
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*
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* Mark it as broken, so that appropriate fallback options can be implemented
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* for architectures that do not define their own _THIS_IP_.
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*/
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#define HAS_BROKEN_THIS_IP
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#endif
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/*
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* _CODE_LOCATION_ provides a unique identifier for the current code location.
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* When _THIS_IP_ is broken (generic version), we fall back to a static marker
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* which guarantees uniqueness and resolves to a constant address at link time,
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* avoiding runtime overhead and compiler optimizations breaking it.
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*/
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#ifdef HAS_BROKEN_THIS_IP
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#define _CODE_LOCATION_ ({ static const char __here; (unsigned long)&__here; })
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#else
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#define _CODE_LOCATION_ _THIS_IP_
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#endif
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#endif /* _LINUX_INSTRUCTION_POINTER_H */
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