On 29/07/2026 13:00, Osama Abdelkader wrote: > On Tue, Jul 28, 2026 at 04:17:14PM +0100, Liviu Dudau wrote: >> On Mon, Jul 20, 2026 at 03:55:18PM +0200, Osama Abdelkader wrote: >>> The firmware exposes the global group count and per-group stream count in >>> the shared control interface. These values are validated before being used >>> as loop bounds, but the memory is shared with the MCU firmware and can be >>> changed after validation. >> >> Again, you're making statements that need to be proven here. How is MCU >> firmware going to change the content of the memory shared with the driver? >> > > Thanks for the review. yes, this was flagged by Sashiko while reviewing the > previous patch, but I agree the commit message shouldn't present it as a > proven > firmware mutation bug. > > The useful part here is just making the validated count the same value used > as the loop bound. since It's an optimisation, should I send v2 without Fixes > and Cc stable tags?
I think the issue here is that Sashiko is thinking the firmware isn't trusted. And there's some truth to that - we do perform validation of the firmware binary and sanity check some of the values it writes. But this is more as a robustness check rather than a real trust boundary. The firmware changing values under the kernel's feet is more than just a robustness bug, it's only really likely to happen with an actually malicious firmware. But the actual change is reasonable, as Liviu says it could even be a (very minor) optimisation. So if you could send a v2 with a reworded commit message then feel free to add: Reviewed-by: Steven Price <[email protected]> Thanks, Steve >>> >>> Read each count once with READ_ONCE() and use the validated snapshot as the >>> loop bound. This keeps the loop bounds consistent with the validation and >>> prevents the compiler from reloading a firmware-controlled count during >>> iteration. >> >> As an optimisation I'm fine with it, so: >> >> Reviewed-by: Liviu Dudau <[email protected]> >> >> Best regards, >> Liviu >> > > Best regards, > Osama >>> >>> Fixes: 2718d91816ee ("drm/panthor: Add the FW logical block") >>> Cc: [email protected] >>> Signed-off-by: Osama Abdelkader <[email protected]> >>> --- >>> drivers/gpu/drm/panthor/panthor_fw.c | 11 +++++++---- >>> 1 file changed, 7 insertions(+), 4 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c >>> b/drivers/gpu/drm/panthor/panthor_fw.c >>> index e2fcbd639c3c..6e6da98d795e 100644 >>> --- a/drivers/gpu/drm/panthor/panthor_fw.c >>> +++ b/drivers/gpu/drm/panthor/panthor_fw.c >>> @@ -959,6 +959,7 @@ static int panthor_init_csg_iface(struct panthor_device >>> *ptdev, >>> u64 shared_section_sz = >>> panthor_kernel_bo_size(ptdev->fw->shared_section->mem); >>> u64 iface_offset = CSF_GROUP_CONTROL_OFFSET + >>> ((u64)csg_idx * glb_iface->control->group_stride); >>> + u32 stream_num; >>> unsigned int i; >>> >>> if (iface_offset > shared_section_sz || >>> @@ -972,8 +973,8 @@ static int panthor_init_csg_iface(struct panthor_device >>> *ptdev, >>> csg_iface->output = iface_fw_to_cpu_addr(ptdev, >>> csg_iface->control->output_va, >>> sizeof(*csg_iface->output)); >>> >>> - if (csg_iface->control->stream_num < MIN_CS_PER_CSG || >>> - csg_iface->control->stream_num > MAX_CS_PER_CSG) >>> + stream_num = READ_ONCE(csg_iface->control->stream_num); >>> + if (stream_num < MIN_CS_PER_CSG || stream_num > MAX_CS_PER_CSG) >>> return -EINVAL; >>> >>> if (!csg_iface->input || !csg_iface->output) { >>> @@ -990,7 +991,7 @@ static int panthor_init_csg_iface(struct panthor_device >>> *ptdev, >>> } >>> } >>> >>> - for (i = 0; i < csg_iface->control->stream_num; i++) { >>> + for (i = 0; i < stream_num; i++) { >>> int ret = panthor_init_cs_iface(ptdev, csg_idx, i); >>> >>> if (ret) >>> @@ -1015,6 +1016,7 @@ static int panthor_fw_init_ifaces(struct >>> panthor_device *ptdev) >>> { >>> struct panthor_fw_global_iface *glb_iface = &ptdev->fw->iface.global; >>> u64 shared_section_sz = >>> panthor_kernel_bo_size(ptdev->fw->shared_section->mem); >>> + u32 group_num; >>> unsigned int i; >>> >>> if (!ptdev->fw->shared_section->mem->kmap) >>> @@ -1034,17 +1036,17 @@ static int panthor_fw_init_ifaces(struct >>> panthor_device *ptdev) >>> return -EINVAL; >>> } >>> >>> - if (glb_iface->control->group_num > MAX_CSGS || >>> - glb_iface->control->group_num < MIN_CSGS) { >>> + group_num = READ_ONCE(glb_iface->control->group_num); >>> + if (group_num > MAX_CSGS || group_num < MIN_CSGS) { >>> drm_err(&ptdev->base, "Invalid number of control groups"); >>> return -EINVAL; >>> } >>> >>> - for (i = 0; i < glb_iface->control->group_num; i++) { >>> + for (i = 0; i < group_num; i++) { >>> int ret = panthor_init_csg_iface(ptdev, i); >>> >>> if (ret) >>> return ret; >>> } >>> >>> drm_info(&ptdev->base, "CSF FW using interface v%d.%d.%d, Features %#x >>> Instrumentation features %#x", >>> -- >>> 2.43.0 >>> >> >> -- >> ==================== >> | I would like to | >> | fix the world, | >> | but they're not | >> | giving me the | >> \ source code! / >> --------------- >> ¯\_(ツ)_/¯
