Re: [PATCH] lib/string: make memzero_explicit inline instead of external

Dave Young
2019-10-10T06:56:00Z

On 10/10/19 at 10:52am, Dave Young wrote:
> On 10/07/19 at 06:00pm, Arvind Sankar wrote:
> > With the use of the barrier implied by barrier_data(), there is no need
> > for memzero_explicit to be extern. Making it inline saves the overhead
> > of a function call, and allows the code to be reused in arch/*/purgatory
> > without having to duplicate the implementation.
> >
> > Fixes: 906a4bb97f5d ("crypto: sha256 - Use get/put_unaligned_be32 to get input, memzero_explicit")
> > Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> > Tested-by: Hans de Goede <hdegoede@redhat.com>
> > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> > ---
> > include/linux/string.h | 21 ++++++++++++++++++++-
> > lib/string.c | 21 ---------------------
> > 2 files changed, 20 insertions(+), 22 deletions(-)
> >
> > diff --git a/include/linux/string.h b/include/linux/string.h
> > index b2f9df7f0761..b6ccdc2c7f02 100644
> > --- a/include/linux/string.h
> > +++ b/include/linux/string.h
> > @@ -227,7 +227,26 @@ static inline bool strstarts(const char *str, const char *prefix)
> > }
> >
> > size_t memweight(const void *ptr, size_t bytes);
> > -void memzero_explicit(void *s, size_t count);
> > +
> > +/**
> > + * memzero_explicit - Fill a region of memory (e.g. sensitive
> > + * keying data) with 0s.
> > + * @s: Pointer to the start of the area.
> > + * @count: The size of the area.
> > + *
> > + * Note: usually using memset() is just fine (!), but in cases
> > + * where clearing out _local_ data at the end of a scope is
> > + * necessary, memzero_explicit() should be used instead in
> > + * order to prevent the compiler from optimising away zeroing.
> > + *
> > + * memzero_explicit() doesn't need an arch-specific version as
> > + * it just invokes the one of memset() implicitly.
> > + */
> > +static inline void memzero_explicit(void *s, size_t count)
> > +{
> > + memset(s, 0, count);
> > + barrier_data(s);
> > +}
> >
> > /**
> > * kbasename - return the last part of a pathname.
> > diff --git a/lib/string.c b/lib/string.c
> > index cd7a10c19210..08ec58cc673b 100644
> > --- a/lib/string.c
> > +++ b/lib/string.c
> > @@ -748,27 +748,6 @@ void *memset(void *s, int c, size_t count)
> > EXPORT_SYMBOL(memset);
> > #endif
> >
> > -/**
> > - * memzero_explicit - Fill a region of memory (e.g. sensitive
> > - * keying data) with 0s.
> > - * @s: Pointer to the start of the area.
> > - * @count: The size of the area.
> > - *
> > - * Note: usually using memset() is just fine (!), but in cases
> > - * where clearing out _local_ data at the end of a scope is
> > - * necessary, memzero_explicit() should be used instead in
> > - * order to prevent the compiler from optimising away zeroing.
> > - *
> > - * memzero_explicit() doesn't need an arch-specific version as
> > - * it just invokes the one of memset() implicitly.
> > - */
> > -void memzero_explicit(void *s, size_t count)
> > -{
> > - memset(s, 0, count);
> > - barrier_data(s);
> > -}
> > -EXPORT_SYMBOL(memzero_explicit);
> > -
> > #ifndef __HAVE_ARCH_MEMSET16
> > /**
> > * memset16() - Fill a memory area with a uint16_t
> > --
>
> Thanks for the fix! Ccing kexec list since the problem is kexec/kdump
> related. People can try it when they see same issue.
>

Also:

Tested-by: Dave Young <dyoung@redhat.com>

Thanks
Dave