58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_INSTRUMENTATION_H
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#define __LINUX_INSTRUMENTATION_H
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#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION)
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/* Begin/end of an instrumentation safe region */
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#define instrumentation_begin() ({ \
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asm volatile("%c0: nop\n\t" \
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".pushsection .discard.instr_begin\n\t" \
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".long %c0b - .\n\t" \
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".popsection\n\t" : : "i" (__COUNTER__)); \
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})
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/*
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* Because instrumentation_{begin,end}() can nest, objtool validation considers
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* _begin() a +1 and _end() a -1 and computes a sum over the instructions.
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* When the value is greater than 0, we consider instrumentation allowed.
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*
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* There is a problem with code like:
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*
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* noinstr void foo()
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* {
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* instrumentation_begin();
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* ...
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* if (cond) {
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* instrumentation_begin();
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* ...
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* instrumentation_end();
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* }
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* bar();
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* instrumentation_end();
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* }
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*
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* If instrumentation_end() would be an empty label, like all the other
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* annotations, the inner _end(), which is at the end of a conditional block,
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* would land on the instruction after the block.
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*
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* If we then consider the sum of the !cond path, we'll see that the call to
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* bar() is with a 0-value, even though, we meant it to happen with a positive
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* value.
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*
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* To avoid this, have _end() be a NOP instruction, this ensures it will be
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* part of the condition block and does not escape.
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*/
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#define instrumentation_end() ({ \
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asm volatile("%c0: nop\n\t" \
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".pushsection .discard.instr_end\n\t" \
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".long %c0b - .\n\t" \
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".popsection\n\t" : : "i" (__COUNTER__)); \
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})
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#else
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# define instrumentation_begin() do { } while(0)
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# define instrumentation_end() do { } while(0)
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#endif
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#endif /* __LINUX_INSTRUMENTATION_H */
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