On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:
> On 24/03/2021 18.20, Joe Perches wrote:
> > On Wed, 2021-03-24 at 09:52 -0700, Joe Perches wrote:
> > > On Wed, 2021-03-24 at 17:42 +0100, Arnd Bergmann wrote:
> > > > On Wed, Mar 24, 2021 at 3:20 PM Joe Perches <[email protected]> wrote:
> > > []
> > > > > > diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
> > > > > []
> > > > > > @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
> > > > > > int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
> > > > > > int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> > > > > >
> > > > > > + if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
> > > > > > + dev_warn(ldb->dev, "%s: invalid mux %d\n",
> > > > > > + __func__, ERR_PTR(mux));
> > > > >
> > > > > This does not compile without warnings.
> > > > >
> > > > > drivers/gpu/drm/imx/imx-ldb.c: In function ‘imx_ldb_encoder_enable’:
> > > > > drivers/gpu/drm/imx/imx-ldb.c:201:22: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘void *’ [-Wformat=]
> > > > > 201 | dev_warn(ldb->dev, "%s: invalid mux %d\n",
> > > > > | ^~~~~~~~~~~~~~~~~~~~~~
> > > > >
> > > > > If you want to use ERR_PTR, the %d should be %pe as ERR_PTR
> > > > > is converting an int a void * to decode the error type and
> > > > > emit it as a string.
> > > >
> > > > Sorry about that.
> > > >
> > > > I decided against using ERR_PTR() in order to also check for
> > > > positive array overflow, but the version I tested was different from
> > > > the version I sent.
> > > >
> > > > v3 coming.
> > >
> > > Thanks. No worries.
> > >
> > > Up to you, vsprintf would emit the positive mux as a funky hashed
> > > hex value by default if you use ERR_PTR with mux > ARRAY_SIZE so
> > > perhaps %d without the ERR_PTR use makes the most sense.
> > >
>
> >
> > Maybe it's better to output non PTR_ERR %pe uses as decimal so this
> > sort of code would work.
>
> No, because that would leak the pointer value when somebody has
> accidentally passed a real kernel pointer to %pe.
I think it's not really an issue.
_All_ code that uses %p<foo> extensions need inspection anyway.
It's already possible to intentionally 'leak' the ptr value
by using %pe, -ptr so I think that's not really an issue.
>
> If the code wants a cute -EFOO string explaining what's wrong, what
> about "%pe", ERR_PTR(mux < 0 : mux : -ERANGE)? Or two separate error
> messages
>
> if (mux < 0)
> ...
> else if (mux >= ARRAY_SIZE())
> ...
Multiple tests, more unnecessary code, multiple format strings, etc...
On 24/03/2021 20.24, Joe Perches wrote:
> On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:
>> On 24/03/2021 18.20, Joe Perches wrote:
>>
>>>
>>> Maybe it's better to output non PTR_ERR %pe uses as decimal so this
>>> sort of code would work.
>>
>> No, because that would leak the pointer value when somebody has
>> accidentally passed a real kernel pointer to %pe.
>
> I think it's not really an issue.
>
> _All_ code that uses %p<foo> extensions need inspection anyway.
There are now a bunch of sanity checks in place that catch e.g. an
ERR_PTR passed to an extension that would derefence the pointer;
enforcing that only ERR_PTRs are passed to %pe (or falling back to %p)
is another of those safeguards.
> It's already possible to intentionally 'leak' the ptr value
> by using %pe, -ptr so I think that's not really an issue.
>
Huh, what? I assume -ptr is shorthand for (void*)-(unsigned long)ptr.
How would that leak the value if ptr is an ordinary kernel pointer?
That's not an ERR_PTR unless (unsigned long)ptr is < 4095 or so.
If you want to print the pointer value just do %px. No need for silly
games. What I'm talking about is preventing _un_intentionally leaking a
valid kernel pointer value. So no, a non-ERR_PTR passed to %pe is not
going to be printed as-is, not in decimal or hexadecimal or roman numerals.
>> If the code wants a cute -EFOO string explaining what's wrong, what
>> about "%pe", ERR_PTR(mux < 0 : mux : -ERANGE)? Or two separate error
>> messages
>>
>> if (mux < 0)
>> ...
>> else if (mux >= ARRAY_SIZE())
>> ...
>
> Multiple tests, more unnecessary code, multiple format strings, etc...
Agreed, I'm not really advocating for the latter; the former suggestion
is IMO a pretty concise way of providing useful information in dmesg.
Rasmus
On Wed, 2021-03-24 at 22:27 +0100, Rasmus Villemoes wrote:
> On 24/03/2021 20.24, Joe Perches wrote:
> > On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:
> > > On 24/03/2021 18.20, Joe Perches wrote:
> > >
> > > >
> > > > Maybe it's better to output non PTR_ERR %pe uses as decimal so this
> > > > sort of code would work.
> > >
> > > No, because that would leak the pointer value when somebody has
> > > accidentally passed a real kernel pointer to %pe.
> >
> > I think it's not really an issue.
> >
> > _All_ code that uses %p<foo> extensions need inspection anyway.
>
> There are now a bunch of sanity checks in place that catch e.g. an
> ERR_PTR passed to an extension that would derefence the pointer;
> enforcing that only ERR_PTRs are passed to %pe (or falling back to %p)
> is another of those safeguards.
>
> > It's already possible to intentionally 'leak' the ptr value
> > by using %pe, -ptr so I think that's not really an issue.
> >
>
> Huh, what? I assume -ptr is shorthand for (void*)-(unsigned long)ptr.
> How would that leak the value if ptr is an ordinary kernel pointer?
> That's not an ERR_PTR unless (unsigned long)ptr is < 4095 or so.
You are confusing ERR_PTR with IS_ERR
ERR_PTR is just
include/linux/err.h:static inline void * __must_check ERR_PTR(long error)
include/linux/err.h-{
include/linux/err.h- return (void *) error;
include/linux/err.h-}f
> If you want to print the pointer value just do %px. No need for silly
> games.
There's no silly game here. %pe would either print a string or a value.
It already does that in 2 cases.