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    SubjectRe: Re: [PATCH v2] arm64: kasan: add interceptors for strcmp/strncmp functions
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    Hello Andrey,

    Thanks for your review.

    On 2018-09-03 오후 6:40, Andrey Ryabinin wrote:
    >
    >
    > On 08/23/2018 11:56 AM, Kyeongdon Kim wrote:
    >
    > > diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
    > > index c3bd520..61ad7f1 100644
    > > --- a/mm/kasan/kasan.c
    > > +++ b/mm/kasan/kasan.c
    > > @@ -304,6 +304,29 @@ void *memcpy(void *dest, const void *src,
    > size_t len)
    > >
    > > return __memcpy(dest, src, len);
    > > }
    > > +#ifdef CONFIG_ARM64
    > > +/*
    > > + * Arch arm64 use assembly variant for strcmp/strncmp,
    > > + * xtensa use inline asm operations and x86_64 use c one,
    > > + * so now this interceptors only for arm64 kasan.
    > > + */
    > > +#undef strcmp
    > > +int strcmp(const char *cs, const char *ct)
    > > +{
    > > + check_memory_region((unsigned long)cs, 1, false, _RET_IP_);
    > > + check_memory_region((unsigned long)ct, 1, false, _RET_IP_);
    > > +
    >
    > Well this is definitely wrong. strcmp() often accesses far more than
    > one byte.
    >
    > > + return __strcmp(cs, ct);
    > > +}
    > > +#undef strncmp
    > > +int strncmp(const char *cs, const char *ct, size_t len)
    > > +{
    > > + check_memory_region((unsigned long)cs, len, false, _RET_IP_);
    > > + check_memory_region((unsigned long)ct, len, false, _RET_IP_);
    >
    > This will cause false positives. Both 'cs', and 'ct' could be less
    > than len bytes.
    >
    > There is no need in these interceptors, just use the C implementations
    > from lib/string.c
    > like you did in your first patch.
    > The only thing that was wrong in the first patch is that assembly
    > implementations
    > were compiled out instead of being declared week.
    >
    Well, at first I thought so..
    I would remove diff code in /mm/kasan/kasan.c then use C implementations
    in lib/string.c
    w/ assem implementations as weak :

    diff --git a/lib/string.c b/lib/string.c
    index 2c0900a..a18b18f 100644
    --- a/lib/string.c
    +++ b/lib/string.c
    @@ -312,7 +312,7 @@ size_t strlcat(char *dest, const char *src, size_t
    count)
     EXPORT_SYMBOL(strlcat);
     #endif

    -#ifndef __HAVE_ARCH_STRCMP
    +#if (defined(CONFIG_ARM64) && defined(CONFIG_KASAN)) ||
    !defined(__HAVE_ARCH_STRCMP)
     /**
      * strcmp - Compare two strings
      * @cs: One string
    @@ -336,7 +336,7 @@ int strcmp(const char *cs, const char *ct)
     EXPORT_SYMBOL(strcmp);
     #endif

    -#ifndef __HAVE_ARCH_STRNCMP
    +#if (defined(CONFIG_ARM64) && defined(CONFIG_KASAN)) ||
    !defined(__HAVE_ARCH_STRNCMP)
     /**
      * strncmp - Compare two length-limited strings

    Can I get your opinion wrt this ?
    Thanks,

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