Re: [PATCH v3 11/12] lkdtm: Fix execute_[user]_location()

[Christophe Leroy <christophe.leroy@xxxxxxxxxx>]

Hi Kees,


Le 17/12/2021 à 12:49, Christophe Leroy a écrit :
> Hi Kees,
>
> Le 17/10/2021 à 14:38, Christophe Leroy a écrit :
> > execute_location() and execute_user_location() intent
> > to copy do_nothing() text and execute it at a new location.
> > However, at the time being it doesn't copy do_nothing() function
> > but do_nothing() function descriptor which still points to the
> > original text. So at the end it still executes do_nothing() at
> > its original location allthough using a copied function descriptor.
> >
> > So, fix that by really copying do_nothing() text and build a new
> > function descriptor by copying do_nothing() function descriptor and
> > updating the target address with the new location.
> >
> > Also fix the displayed addresses by dereferencing do_nothing()
> > function descriptor.
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>
> Do you have any comment to this patch and to patch 12 ?
>
> If not, is it ok to get your acked-by ?

Any feedback please, even if it's to say no feedback ?

Many thanks,
Christophe

> Thanks
> Christophe
>
> > ---
> >   drivers/misc/lkdtm/perms.c | 37 ++++++++++++++++++++++++++++---------
> >   1 file changed, 28 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> > index 035fcca441f0..1cf24c4a79e9 100644
> > --- a/drivers/misc/lkdtm/perms.c
> > +++ b/drivers/misc/lkdtm/perms.c
> > @@ -44,19 +44,34 @@ static noinline void do_overwritten(void)
> >       return;
> >   }
> > +static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
> > +{
> > +    if (!have_function_descriptors())
> > +        return dst;
> > +
> > +    memcpy(fdesc, do_nothing, sizeof(*fdesc));
> > +    fdesc->addr = (unsigned long)dst;
> > +    barrier();
> > +
> > +    return fdesc;
> > +}
> > +
> >   static noinline void execute_location(void *dst, bool write)
> >   {
> > -    void (*func)(void) = dst;
> > +    void (*func)(void);
> > +    func_desc_t fdesc;
> > +    void *do_nothing_text = dereference_function_descriptor(do_nothing);
> > -    pr_info("attempting ok execution at %px\n", do_nothing);
> > +    pr_info("attempting ok execution at %px\n", do_nothing_text);
> >       do_nothing();
> >       if (write == CODE_WRITE) {
> > -        memcpy(dst, do_nothing, EXEC_SIZE);
> > +        memcpy(dst, do_nothing_text, EXEC_SIZE);
> >           flush_icache_range((unsigned long)dst,
> >                      (unsigned long)dst + EXEC_SIZE);
> >       }
> > -    pr_info("attempting bad execution at %px\n", func);
> > +    pr_info("attempting bad execution at %px\n", dst);
> > +    func = setup_function_descriptor(&fdesc, dst);
> >       func();
> >       pr_err("FAIL: func returned\n");
> >   }
> > @@ -66,16 +81,19 @@ static void execute_user_location(void *dst)
> >       int copied;
> >       /* Intentionally crossing kernel/user memory boundary. */
> > -    void (*func)(void) = dst;
> > +    void (*func)(void);
> > +    func_desc_t fdesc;
> > +    void *do_nothing_text = dereference_function_descriptor(do_nothing);
> > -    pr_info("attempting ok execution at %px\n", do_nothing);
> > +    pr_info("attempting ok execution at %px\n", do_nothing_text);
> >       do_nothing();
> > -    copied = access_process_vm(current, (unsigned long)dst, do_nothing,
> > +    copied = access_process_vm(current, (unsigned long)dst, 
> > do_nothing_text,
> >                      EXEC_SIZE, FOLL_WRITE);
> >       if (copied < EXEC_SIZE)
> >           return;
> > -    pr_info("attempting bad execution at %px\n", func);
> > +    pr_info("attempting bad execution at %px\n", dst);
> > +    func = setup_function_descriptor(&fdesc, dst);
> >       func();
> >       pr_err("FAIL: func returned\n");
> >   }
> > @@ -153,7 +171,8 @@ void lkdtm_EXEC_VMALLOC(void)
> >   void lkdtm_EXEC_RODATA(void)
> >   {
> > -    execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
> > +    
> > execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing), 
> >
> > +             CODE_AS_IS);
> >   }
> >   void lkdtm_EXEC_USERSPACE(void)