On Wed, Jul 22, 2020 at 6:53 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > > These are back again. Please take a look at them. I'm fairly sure these > are all 'safe' but really don't like taking patches without the surety of > a second pair of eyes having taken a look at them. That is particularly > true of fixes for long term issues like these ones. > So, for all non-commented Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> with a condition that you amend comments in the code. I see that they can be categorized into three categories: 1. struct approach (no [big] comment needed, we have __aligned self-explanatory) 2. dynamic channels (nothing specifically needed, perhaps mention "the amount of channels is defined at run-time" or alike) 3. the rest of non-standard cases where per case comment is needed. Above applies to a subset of commented patches (where my comment about the topic). The rest I will look at v4. Thanks! > Changes since v2: > * bmc150-accel: Use sizeof() for channel size (Andy Shevchenko) > * st_uvis25: Use local variable for regmap call (Andy Shevchenko) > * st_lsm6dsx: Use array of scan[] rather than 3 structures (Lorenzo Bianconi) > * inv_mpu6050: Add patch switching to a regmap_noinc_read (Jean-Baptiste Maneyrol) > * ina2xx: Use a structure (previously failed to notice that works here) > * I've added clarifying notes to patch descriptions based on questions asked. > These were mainly about why we didn't use the structure approach everywhere > and why I've forced alignment in places it wasn't strictly needed. > > Previous cover letter: > A few notes based on questions on v1. > > 1. Why not use put_unaligned to avoid the whole thing? > This interface can pass directly to a variety of in kernel users > who would reasonably assume that we have true natural alignment. > When it gets passed directly is subtle as it depends on whether > the demux has to realign the data or not. So enabling an extra > channel could result in a previously working alignment no longer > being true. > > Even if this is fine for existing usecases we are likely to > store up subtle long term issues if we don't fix it explicitly. > It's also worth noting that the data channel sometimes suffered > the same problem as the timestamp. > > 2. Why not specify explicit padding? > In my view this is error prone in comparisom with relying on > c to do the hard work for us. > > 3. Why not move the timestamp to the start? > ABI breakage and as timestamp is optional (no obvious from the > iio_push_to_buffers_with_timestamp call) we can end up having > to shift the rest of the data within that call. > > Changes since v1. > > Andy Schevchenko pointed out that on x86_32 s64 elements are only > aligned to 4 bytes. Where I had tried to use a structure to avoid > explicit need to list the padding, there were some cases where > this results in insufficient padding being inserted. > > This doesn't affect the few patches that had already been applied and > sent upstream. (which was lucky ;) > > The fix was to take advantage of __aligned(8) which (according to > my reading of the c spec and the gcc docs) enforces the alignment of > both the element within a structure and the structure itself. > The kernel now requires a recent enough version of GCC to ensure this > works both on the stack and heap. This is done in lots of other > userspace interfaces. In some cases iio_push_to_buffers_with_ts > is aligning data for passing to userspace, be it via a kfifo > so it is sensible we should use the same solution. > > Note that we could have used u64_aligned but there is no equivalent > for s64 and explicit use of __aligned(8) is common in > the kernel so we adopt this here. > > Note that there were about 8 drivers that would have been broken with > v1 of the patch. I have also forced alignment of timestamps in cases > where (mostly by coincidence) we would have been fine (padding was > less than 4 bytes anyway. I did this partly to reduce fragility if > other elements are added in future and also to avoid cut and paste > errors in new drivers. > > There were a few other minor tidying up changes inline with reviews > of v1. > > I've kept tags given for v1 on basis the changes are minor. Shout if > you disagree. > > Version 1 part 1 cover letter. > > Lars noted in a recent review [1] of the adis16475 that we had an issue around > the alignment requirements of iio_push_to_buffers_with_timestamp. > Whilst it's not documented, that function assumes that the overall buffer > is 8 byte aligned, to ensure the timestamp is itself naturally aligned. > We have drivers that use arrays (typically on the stack) that do > not guarantee this alignment. > > We could have fixed this by using a put_unaligned to write the timestamp > but I think that just pushes the problem down the line. If we were to > have a consumer buffer wanting all the channels in the current > active_scanmask then it will get the raw buffer from the driver passed > straight through. It seems odd to me if we allow passing a buffer > that is not naturally aligned through to a consumer. > Hence I'm proposing to fix up all existing drivers that might pass > a buffer with insufficient alignment guarantees. > Sometimes the timestamp is guaranteed to be in a particular location, > in which case we can use C structure alignment guarantees to fix this > in a nice readable fashion. In other cases, the timestamp location > depends on which channels are enabled, and in those case we can > use explicit alignment __aligned(8) to ensure the whole array is > appropriately aligned. > > Lars-Peter also noted that, in many of these cases, there are holes > in the stack array that we never write. Those provide a potential > leak of kernel data to userspace. For drivers where this applies > we either need to zero those holes each time, or allocate the buffer > on the heap (only once), ensuring it is zeroed at that time. > We may leak previous values from the sensor but currently that seems > unlikely to present any form of security risk. > > As such, this first set contains a mixture of fixes. Where there > are no possible holes, the buffer is kept on the stack but a > c structure is used to guarantee appropriate alignment. Where > there are holes, the buffer is moved into the iio_priv() accessed > data private structure. A c structure or __aligned(8) is used > as appropriate. > > I've stopped at this point rather than doing all the drivers Lars > found in order to both throttle the review burden and also to > see find any general problems with the fixes before doign futher > similar series. A few of the remaining ones will be rather more > complex to deal with. > > These have been there a long time, so whilst they are fixes we > will want in stable I'm not that bothered if it takes us a little > while to get them there! > > [1] https://www.spinics.net/lists/devicetree/msg350590.html > [2] https://patchwork.kernel.org/cover/11554215/ > > Jonathan Cameron (27): > iio: accel: kxsd9: Fix alignment of local buffer. > iio:accel:mma8452: Fix timestamp alignment and prevent data leak. > iio:accel:bmc150-accel: Fix timestamp alignment and prevent data leak. > iio:accel:mma7455: Fix timestamp alignment and prevent data leak. > iio:gyro:itg3200: Fix timestamp alignment and prevent data leak. > iio:proximity:mb1232: Fix timestamp alignment and prevent data leak. > iio:chemical:ccs811: Fix timestamp alignment and prevent data leak. > iio:light:si1145: Fix timestamp alignment and prevent data leak. > iio:light:max44000 Fix timestamp alignment and prevent data leak. > iio:light:rpr0521 Fix timestamp alignment and prevent data leak. > iio:light:st_uvis25 Fix timestamp alignment and prevent data leak. > iio:light:ltr501 Fix timestamp alignment issue. > iio:magnetometer:ak8975 Fix alignment and data leak issues. > iio:magnetometer:mag3110 Fix alignment and data leak issues. > iio:imu:bmi160 Fix alignment and data leak issues > iio:imu:st_lsm6dsx Fix alignment and data leak issues > iio:imu:inv_mpu6050 Fix dma and ts alignment and data leak issues. > iio:imu:inv_mpu6050: Use regmap_noinc_read for fifo reads. > iio:pressure:mpl3115 Force alignment of buffer > iio:adc:ti-adc081c Fix alignment and data leak issues > iio:adc:ti-adc084s021 Fix alignment and data leak issues. > iio:adc:ti-adc084s021 Tidy up endian types > iio:adc:ti-ads124s08 Fix alignment and data leak issues. > iio:adc:ti-adc0832 Fix alignment issue with timestamp > iio:adc:ti-adc12138 Fix alignment issue with timestamp > iio:adc:ina2xx Fix timestamp alignment issue. > iio:adc:max1118 Fix alignment of timestamp and data leak issues > > drivers/iio/accel/bmc150-accel-core.c | 15 ++++++-- > drivers/iio/accel/kxsd9.c | 16 ++++++--- > drivers/iio/accel/mma7455_core.c | 16 ++++++--- > drivers/iio/accel/mma8452.c | 11 ++++-- > drivers/iio/adc/ina2xx-adc.c | 11 +++--- > drivers/iio/adc/max1118.c | 10 ++++-- > drivers/iio/adc/ti-adc081c.c | 11 ++++-- > drivers/iio/adc/ti-adc0832.c | 7 ++-- > drivers/iio/adc/ti-adc084s021.c | 20 ++++++----- > drivers/iio/adc/ti-adc12138.c | 9 ++--- > drivers/iio/adc/ti-ads124s08.c | 10 ++++-- > drivers/iio/chemical/ccs811.c | 13 ++++--- > drivers/iio/gyro/itg3200_buffer.c | 15 +++++--- > drivers/iio/imu/bmi160/bmi160.h | 2 ++ > drivers/iio/imu/bmi160/bmi160_core.c | 5 ++- > drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h | 8 +++-- > drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c | 14 ++++---- > drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h | 6 ++++ > .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 36 ++++++++++--------- > drivers/iio/light/ltr501.c | 15 ++++---- > drivers/iio/light/max44000.c | 12 ++++--- > drivers/iio/light/rpr0521.c | 17 ++++++--- > drivers/iio/light/si1145.c | 7 ++-- > drivers/iio/light/st_uvis25.h | 5 +++ > drivers/iio/light/st_uvis25_core.c | 8 +++-- > drivers/iio/magnetometer/ak8975.c | 16 ++++++--- > drivers/iio/magnetometer/mag3110.c | 13 ++++--- > drivers/iio/pressure/mpl3115.c | 3 +- > drivers/iio/proximity/mb1232.c | 17 ++++----- > 29 files changed, 229 insertions(+), 119 deletions(-) > > -- > 2.27.0 > -- With Best Regards, Andy Shevchenko
