linux-hardening - Re: [PATCH v2 61/63] powerpc: Split memset() to avoid multi-field overflow

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Date:   Wed, 18 Aug 2021 15:30:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Wang Wensheng <wangwensheng4@...wei.com>,
        linux-staging@...ts.linux.dev, linux-wireless@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Qinglang Miao <miaoqinglang@...wei.com>,
        linux-block@...r.kernel.org, Hulk Robot <hulkci@...wei.com>,
        clang-built-linux@...glegroups.com, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kbuild@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 61/63] powerpc: Split memset() to avoid multi-field
 overflow

On Wed, Aug 18, 2021 at 08:42:18AM +0200, Christophe Leroy wrote:
> 
> 
> Le 18/08/2021 à 08:05, Kees Cook a écrit :
> > In preparation for FORTIFY_SOURCE performing compile-time and run-time
> > field bounds checking for memset(), avoid intentionally writing across
> > neighboring fields.
> > 
> > Instead of writing across a field boundary with memset(), move the call
> > to just the array, and an explicit zeroing of the prior field.
> > 
> > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > Cc: Qinglang Miao <miaoqinglang@...wei.com>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: Hulk Robot <hulkci@...wei.com>
> > Cc: Wang Wensheng <wangwensheng4@...wei.com>
> > Cc: linuxppc-dev@...ts.ozlabs.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Reviewed-by: Michael Ellerman <mpe@...erman.id.au>
> > Link: https://lore.kernel.org/lkml/87czqsnmw9.fsf@mpe.ellerman.id.au
> > ---
> >   drivers/macintosh/smu.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/macintosh/smu.c b/drivers/macintosh/smu.c
> > index 94fb63a7b357..59ce431da7ef 100644
> > --- a/drivers/macintosh/smu.c
> > +++ b/drivers/macintosh/smu.c
> > @@ -848,7 +848,8 @@ int smu_queue_i2c(struct smu_i2c_cmd *cmd)
> >   	cmd->read = cmd->info.devaddr & 0x01;
> >   	switch(cmd->info.type) {
> >   	case SMU_I2C_TRANSFER_SIMPLE:
> > -		memset(&cmd->info.sublen, 0, 4);
> > +		cmd->info.sublen = 0;
> > +		memset(&cmd->info.subaddr, 0, 3);
> 
> subaddr[] is a table, should the & be avoided ?

It results in the same thing, but it's better form to not have the &; I
will fix this.

> And while at it, why not use sizeof(subaddr) instead of 3 ?

Agreed. :)

Thanks!

-- 
Kees Cook