linux-kernel - Re: [PATCH] x86, asm-generic: add KASAN instrumentation to bitops

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Date:   Thu, 30 Mar 2017 09:03:54 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     mark.rutland@....com, peterz@...radead.org,
        aryabinin@...tuozzo.com, akpm@...ux-foundation.org,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86, asm-generic: add KASAN instrumentation to bitops


* Dmitry Vyukov <dvyukov@...gle.com> wrote:

> +#include <asm-generic/bitops-instrumented.h>
> +
>  #include <asm-generic/bitops/find.h>
>  
>  #include <asm-generic/bitops/sched.h>
> diff --git a/include/asm-generic/bitops-instrumented.h b/include/asm-generic/bitops-instrumented.h
> new file mode 100644
> index 000000000000..01d02113fc7e
> --- /dev/null
> +++ b/include/asm-generic/bitops-instrumented.h
> @@ -0,0 +1,53 @@
> +/* See atomic-instrumented.h for explanation. */
> +#ifndef _LINUX_BITOPS_INSTRUMENTED_H
> +#define _LINUX_BITOPS_INSTRUMENTED_H
> +
> +#include <linux/kasan-checks.h>
> +
> +#define ADDR(nr, addr) ((void *)(addr) + ((nr) >> 3))
> +
> +#define INSTR_VOID(func)						\
> +static __always_inline void func(long nr, volatile unsigned long *addr)	\
> +{									\
> +	kasan_check_write(ADDR(nr, addr), 1);				\
> +	arch_##func(nr, addr);						\
> +}
> +
> +#define INSTR_BOOL(func)						\
> +static __always_inline bool func(long nr, volatile unsigned long *addr)	\
> +{									\
> +	kasan_check_write(ADDR(nr, addr), 1);				\
> +	return arch_##func(nr, addr);					\
> +}

Is the 'ADDR()' construct going to result in any extra inlined instructions in an 
instrumented kernel? If yes, why not do it inside the KASAN callback to reduce 
inlining overhead?

> +INSTR_VOID(set_bit);
> +INSTR_VOID(__set_bit);
> +INSTR_VOID(clear_bit);
> +INSTR_VOID(__clear_bit);
> +INSTR_VOID(clear_bit_unlock);
> +INSTR_VOID(__clear_bit_unlock);
> +INSTR_VOID(change_bit);
> +INSTR_VOID(__change_bit);
> +
> +INSTR_BOOL(test_and_set_bit);
> +INSTR_BOOL(test_and_set_bit_lock);
> +INSTR_BOOL(__test_and_set_bit);
> +INSTR_BOOL(test_and_clear_bit);
> +INSTR_BOOL(__test_and_clear_bit);
> +INSTR_BOOL(test_and_change_bit);
> +INSTR_BOOL(__test_and_change_bit);
> +#ifdef clear_bit_unlock_is_negative_byte
> +INSTR_BOOL(clear_bit_unlock_is_negative_byte);
> +#endif
> +
> +static bool test_bit(int nr, const volatile unsigned long *addr)
> +{
> +	kasan_check_read(ADDR(nr, addr), 1);
> +	return arch_test_bit(nr, addr);
> +}

Same objections as to the atomic primitives: don't hide function signatures behind 
CPP complexity for marginal line count reduction.

Thanks,

	Ingo