On 26 March 2018 at 08:33, Tobin C. Harding <me@xxxxxxxx> wrote: > The use of stack Variable Length Arrays needs to be avoided, as they > can be a vector for stack exhaustion, which can be both a runtime bug > (kernel Oops) or a security flaw (overwriting memory beyond the > stack). Also, in general, as code evolves it is easy to lose track of > how big a VLA can get. Thus, we can end up having runtime failures > that are hard to debug. As part of the directive[1] to remove all VLAs > from the kernel, and build with -Wvla. > > Currently driver is using a VLA declared using the number of descriptors. This > array is used to store integer values and is later used as an argument to > `gpiod_set_array_value_cansleep()` This can be avoided by using > `kmalloc_array()` to allocate memory for the array of integer values. Memory is > free'd before return from function. > > From the code it appears that it is safe to sleep so we can use GFP_KERNEL > (based _cansleep() suffix of function `gpiod_set_array_value_cansleep()`. > > It can be expected that this patch will result in a small increase in overhead > due to the use of `kmalloc_array()` > > [1] https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Tobin C. Harding <me@xxxxxxxx> Thanks, queued for 3.18! Kind regards Uffe > --- > > Patch is untested. I was not able to fully grok the call chain involved > with this change so was unable to quantify the total degradation > of performance. > > Line calling to gpiod_set_array_value_cansleep() is 83 characters long, > patch attempts to leave the code as clean as possible. Open to > suggestions for improvement. I tried various forms of while loop and > pointer arithmetic for the setting of `values` but in the end settled > for array indexing, again open to suggestions. > > thanks, > Tobin. > > drivers/mmc/core/pwrseq_simple.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/drivers/mmc/core/pwrseq_simple.c b/drivers/mmc/core/pwrseq_simple.c > index 13ef162cf066..a8b9fee4d62a 100644 > --- a/drivers/mmc/core/pwrseq_simple.c > +++ b/drivers/mmc/core/pwrseq_simple.c > @@ -40,14 +40,18 @@ static void mmc_pwrseq_simple_set_gpios_value(struct mmc_pwrseq_simple *pwrseq, > struct gpio_descs *reset_gpios = pwrseq->reset_gpios; > > if (!IS_ERR(reset_gpios)) { > - int i; > - int values[reset_gpios->ndescs]; > + int i, *values; > + int nvalues = reset_gpios->ndescs; > > - for (i = 0; i < reset_gpios->ndescs; i++) > + values = kmalloc_array(nvalues, sizeof(int), GFP_KERNEL); > + if (!values) > + return; > + > + for (i = 0; i < nvalues; i++) > values[i] = value; > > - gpiod_set_array_value_cansleep( > - reset_gpios->ndescs, reset_gpios->desc, values); > + gpiod_set_array_value_cansleep(nvalues, reset_gpios->desc, values); > + kfree(values); > } > } > > -- > 2.7.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
