Messages in this thread Patch in this message | | | Date | Thu, 22 Apr 2021 12:34:52 +0100 | From | Cristian Marussi <> | Subject | Re: [PATCH] firmware: arm_scpi: prevent ternary sign expansion bug |
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On Thu, Apr 22, 2021 at 11:17:09AM +0100, Cristian Marussi wrote: > Hi, > > On Thu, Apr 22, 2021 at 12:02:29PM +0300, Dan Carpenter wrote: > > How type promotion works in ternary expressions is a bit tricky. > > The problem is that scpi_clk_get_val() returns longs, "ret" is a int > > which holds a negative error code, and le32_to_cpu() is an unsigned int. > > We want the negative error code to be cast to a negative long. But > > because le32_to_cpu() is an u32 then "ret" is type promoted to u32 and > > becomes a high positive and then it is promoted to long and it is still > > a high positive value. > > > > Fix this by getting rid of the ternary. > > I wonder how/if the callers up in the stack check/expect ever effectively for a > 2-complement negative value inside the returned unsigned long...given that this > plugs finally into CLK framework struct clk_ops.recalc_rate via clk-scpi.c which > also expects unsigned long....but that's another story. > > FWIW regarding this patch: > > Reviewed-by: Cristian Marussi <cristian.marussi@arm.com> > > Thanks > > Cristian
@Sudeep, as a second though, looking at .recalc_rate() definition inside
include/linux/clk-provider.h:struct clk_ops
which is the direct caller of this SCPI clk function, I wonder if, instead, on error we should not return here just ZERO as the returned clock rate value as in:
if (ret) return 0;
given that the error code returned inside the unsigned long won't be ever considerd as such apparently, so not sure if it'd be worst to return a very big fake value or zero...
Thanks Cristian
> > > > Fixes: 8cb7cf56c9fe ("firmware: add support for ARM System Control and Power Interface(SCPI) protocol") > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> > > --- > > drivers/firmware/arm_scpi.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/firmware/arm_scpi.c b/drivers/firmware/arm_scpi.c > > index d0dee37ad522..3bf61854121d 100644 > > --- a/drivers/firmware/arm_scpi.c > > +++ b/drivers/firmware/arm_scpi.c > > @@ -552,8 +552,10 @@ static unsigned long scpi_clk_get_val(u16 clk_id) > > > > ret = scpi_send_message(CMD_GET_CLOCK_VALUE, &le_clk_id, > > sizeof(le_clk_id), &rate, sizeof(rate)); > > + if (ret) > > + return ret; > > > > - return ret ? ret : le32_to_cpu(rate); > > + return le32_to_cpu(rate); > > } > > > > static int scpi_clk_set_val(u16 clk_id, unsigned long rate) > > -- > > 2.30.2 > >
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