Hi David,
On Fri, 9 Aug 2019 at 05:53, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Aug 01, 2019 at 01:11:29PM -0600, Simon Glass wrote:
> > Hi David,
> >
> > On Mon, 22 Jul 2019 at 01:25, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Sat, Jul 20, 2019 at 05:31:09PM -0600, Simon Glass wrote:
> > > > This file provides read-write access to the device tree and includes
> > > > mostly checks of the header. Allow these checks to be disabled to reduce
> > > > code size.
> > > >
> > > > Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> > > > ---
> > > >
> > > > libfdt/fdt_rw.c | 14 ++++++++++----
> > > > 1 file changed, 10 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/libfdt/fdt_rw.c b/libfdt/fdt_rw.c
> > > > index 8795947..4ff3aab 100644
> > > > --- a/libfdt/fdt_rw.c
> > > > +++ b/libfdt/fdt_rw.c
> > > > @@ -13,6 +13,8 @@
> > > > static int fdt_blocks_misordered_(const void *fdt,
> > > > int mem_rsv_size, int struct_size)
> > > > {
> > > > + if (!_check2())
> > > > + return false;
> > >
> > > I think this needs to be check1. An fdt with the blocks in the
> > > "wrong" order isn't actually invalid - it's just inconvenient for our
> > > purposes here. So if you disable this check, you're potentially
> > > making this misbehave on valid blobs, not merely trusting that the
> > > blob you have is valid.
> >
> > Yes, fixed.
> >
> > >
> > > > return (fdt_off_mem_rsvmap(fdt) < FDT_ALIGN(sizeof(struct fdt_header), 8))
> > > > || (fdt_off_dt_struct(fdt) <
> > > > (fdt_off_mem_rsvmap(fdt) + mem_rsv_size))
> > > > @@ -24,6 +26,8 @@ static int fdt_blocks_misordered_(const void *fdt,
> > > >
> > > > static int fdt_rw_probe_(void *fdt)
> > > > {
> > > > + if (!_check2())
> > > > + return 0;
> > > > FDT_RO_PROBE(fdt);
> > > >
> > > > if (fdt_version(fdt) < 17)
> > > > @@ -40,7 +44,7 @@ static int fdt_rw_probe_(void *fdt)
> > > > #define FDT_RW_PROBE(fdt) \
> > > > { \
> > > > int err_; \
> > > > - if ((err_ = fdt_rw_probe_(fdt)) != 0) \
> > > > + if (_check2() && (err_ = fdt_rw_probe_(fdt)) != 0) \
> > > > return err_; \
> > > > }
> > > >
> > > > @@ -120,7 +124,8 @@ static int fdt_find_add_string_(void *fdt, const char *s, int *allocated)
> > > > int len = strlen(s) + 1;
> > > > int err;
> > > >
> > > > - *allocated = 0;
> > > > + if (_check1())
> > > > + *allocated = 0;
> > > >
> > > > p = fdt_find_string_(strtab, fdt_size_dt_strings(fdt), s);
> > > > if (p)
> > > > @@ -132,7 +137,8 @@ static int fdt_find_add_string_(void *fdt, const char *s, int *allocated)
> > > > if (err)
> > > > return err;
> > > >
> > > > - *allocated = 1;
> > > > + if (_check1())
> > > > + *allocated = 1;
> > >
> > > IIUC you're also using the check level to avoid searching for an
> > > existing string and just adding it (possibly duplicated). That's
> > > potentially a useful thing - I've had other requests for that to avoid
> > > a potentially slow string search. However, I'm a bit uncomfortable
> > > with hooking it to something that's allegedly just about checking.
> > > This will change the behaviour of the library even on correct blobs.
> >
> > I don't think so. It's just that if we don't care whether the string
> > was found or allocated, unless we want to delete the string when we
> > run out of space. This new feature was not present earlier, and wastes
> > code space if you don't care.
>
> It's true that we don't usually care whether the string is found or
> allocated. But - for a correct starting dt and correct usage - your
> other changes will result in byte-for-byte identical output. This one
> won't.
Yes that's right. Of course this is how it used to work until
recently, and running out of space is an error condition.
So should I change it to always enable this code except when all
checks are disabled?
>
> > Part of the problem is that fdt_find_add_string_() has no function
> > comment, so I'll have a crack at adding one.
> >
> > >
> > > >
> > > > memcpy(new, s, len);
> > > > return (new - strtab);
> > > > @@ -206,7 +212,7 @@ static int fdt_add_property_(void *fdt, int nodeoffset, const char *name,
> > > >
> > > > err = fdt_splice_struct_(fdt, *prop, 0, proplen);
> > > > if (err) {
> > > > - if (allocated)
> > > > + if (_check1() && allocated)
> > > > fdt_del_last_string_(fdt, name);
> > > > return err;
> > > > }
> >
> > Regards,
> > Simon
> >
Regards,
Simon
