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Message-ID: <202504071336.0C708FCAB8@keescook>
Date: Mon, 7 Apr 2025 13:39:56 -0700
From: Kees Cook <kees@...nel.org>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/nouveau: chan: Avoid
-Wflex-array-member-not-at-end warnings
On Mon, Apr 07, 2025 at 01:57:48PM -0600, Gustavo A. R. Silva wrote:
>
>
> On 07/04/25 13:50, Kees Cook wrote:
> > On Thu, Apr 03, 2025 at 10:45:18AM -0600, Gustavo A. R. Silva wrote:
> > > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> > > getting ready to enable it, globally.
> > >
> > > Use the `DEFINE_RAW_FLEX()` helper for a few on-stack definitions
> > > of a flexible structure where the size of the flexible-array member
> > > is known at compile-time, and refactor the rest of the code,
> > > accordingly.
> > >
> > > So, with these changes, fix the following warnings:
> > >
> > > drivers/gpu/drm/nouveau/nouveau_chan.c:274:37: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > > drivers/gpu/drm/nouveau/nouveau_chan.c:371:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > > drivers/gpu/drm/nouveau/nouveau_chan.c:524:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > >
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> > > ---
> > > drivers/gpu/drm/nouveau/nouveau_chan.c | 115 ++++++++++++-------------
> > > 1 file changed, 56 insertions(+), 59 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > > index cd659b9fd1d9..a7e70517b7cd 100644
> > > --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> > > +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > > @@ -270,10 +270,7 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
> > > { NV03_CHANNEL_DMA , 0 },
> > > {}
> > > };
> > > - struct {
> > > - struct nvif_chan_v0 chan;
> > > - char name[TASK_COMM_LEN+16];
> > > - } args;
> > > + DEFINE_RAW_FLEX(struct nvif_chan_v0, args, name, TASK_COMM_LEN + 16);
> > > struct nvif_device *device = &cli->device;
> > > struct nouveau_channel *chan;
> > > const u64 plength = 0x10000;
> > > @@ -298,28 +295,28 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
> > > return ret;
> > > /* create channel object */
> > > - args.chan.version = 0;
> > > - args.chan.namelen = sizeof(args.name);
> > > - args.chan.runlist = __ffs64(runm);
> > > - args.chan.runq = 0;
> > > - args.chan.priv = priv;
> > > - args.chan.devm = BIT(0);
> > > + args->version = 0;
> > > + args->namelen = __struct_size(args) - sizeof(*args);
> >
> > Does __struct_size(args->name) work here (and later)?
>
> Why not?
Uhm, I'm genuinely curious. I *think* it will work, but because it's
within the struct, not outside of it, I'm unclear if it'll DTRT for
finding the size (since __builtin_object_size() can be touchy).
> I mean, this should be equivalent to `TASK_COMM_LEN+16`, I could
> use the latter if people prefer it (see my comments below).
Right, it should be the same. I think __struct_size(args->name) would be
much more readable ... if it works. :)
>
> >
> > > + args->runlist = __ffs64(runm);
> > > + args->runq = 0;
> > > + args->priv = priv;
> > > + args->devm = BIT(0);
> > > if (hosts[cid].oclass < NV50_CHANNEL_GPFIFO) {
> > > - args.chan.vmm = 0;
> > > - args.chan.ctxdma = nvif_handle(&chan->push.ctxdma);
> > > - args.chan.offset = chan->push.addr;
> > > - args.chan.length = 0;
> > > + args->vmm = 0;
> > > + args->ctxdma = nvif_handle(&chan->push.ctxdma);
> > > + args->offset = chan->push.addr;
> > > + args->length = 0;
> > > } else {
> > > - args.chan.vmm = nvif_handle(&chan->vmm->vmm.object);
> > > + args->vmm = nvif_handle(&chan->vmm->vmm.object);
> > > if (hosts[cid].oclass < FERMI_CHANNEL_GPFIFO)
> > > - args.chan.ctxdma = nvif_handle(&chan->push.ctxdma);
> > > + args->ctxdma = nvif_handle(&chan->push.ctxdma);
> > > else
> > > - args.chan.ctxdma = 0;
> > > - args.chan.offset = ioffset + chan->push.addr;
> > > - args.chan.length = ilength;
> > > + args->ctxdma = 0;
> > > + args->offset = ioffset + chan->push.addr;
> > > + args->length = ilength;
> > > }
> > > - args.chan.huserd = 0;
> > > - args.chan.ouserd = 0;
> > > + args->huserd = 0;
> > > + args->ouserd = 0;
> > > /* allocate userd */
> > > if (hosts[cid].oclass >= VOLTA_CHANNEL_GPFIFO_A) {
> > > @@ -329,27 +326,28 @@ nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
> > > if (ret)
> > > return ret;
> > > - args.chan.huserd = nvif_handle(&chan->mem_userd.object);
> > > - args.chan.ouserd = 0;
> > > + args->huserd = nvif_handle(&chan->mem_userd.object);
> > > + args->ouserd = 0;
> > > chan->userd = &chan->mem_userd.object;
> > > } else {
> > > chan->userd = &chan->user;
> > > }
> > > - snprintf(args.name, sizeof(args.name), "%s[%d]", current->comm, task_pid_nr(current));
> > > + snprintf(args->name, __struct_size(args) - sizeof(*args), "%s[%d]",
> > > + current->comm, task_pid_nr(current));
> > > ret = nvif_object_ctor(&device->object, "abi16ChanUser", 0, hosts[cid].oclass,
> > > - &args, sizeof(args), &chan->user);
> > > + args, __struct_size(args), &chan->user);
> > > if (ret) {
> > > nouveau_channel_del(pchan);
> > > return ret;
> > > }
> > > - chan->runlist = args.chan.runlist;
> > > - chan->chid = args.chan.chid;
> > > - chan->inst = args.chan.inst;
> > > - chan->token = args.chan.token;
> > > + chan->runlist = args->runlist;
> > > + chan->chid = args->chid;
> > > + chan->inst = args->inst;
> > > + chan->token = args->token;
> > > return 0;
> > > }
> > > @@ -367,17 +365,17 @@ nouveau_channel_init(struct nouveau_channel *chan, u32 vram, u32 gart)
> > > return ret;
> > > if (chan->user.oclass >= FERMI_CHANNEL_GPFIFO) {
> > > - struct {
> > > - struct nvif_event_v0 base;
> > > - struct nvif_chan_event_v0 host;
> > > - } args;
> > > + DEFINE_RAW_FLEX(struct nvif_event_v0, args, data,
> > > + sizeof(struct nvif_chan_event_v0));
> > > + struct nvif_chan_event_v0 *host =
> > > + (struct nvif_chan_event_v0 *)args->data;
> > > - args.host.version = 0;
> > > - args.host.type = NVIF_CHAN_EVENT_V0_KILLED;
> > > + host->version = 0;
> > > + host->type = NVIF_CHAN_EVENT_V0_KILLED;
> > > ret = nvif_event_ctor(&chan->user, "abi16ChanKilled", chan->chid,
> > > nouveau_channel_killed, false,
> > > - &args.base, sizeof(args), &chan->kill);
> > > + args, __struct_size(args), &chan->kill);
> > > if (ret == 0)
> > > ret = nvif_event_allow(&chan->kill);
> > > if (ret) {
> > > @@ -520,46 +518,45 @@ nouveau_channels_fini(struct nouveau_drm *drm)
> > > int
> > > nouveau_channels_init(struct nouveau_drm *drm)
> > > {
> > > - struct {
> > > - struct nv_device_info_v1 m;
> > > - struct {
> > > - struct nv_device_info_v1_data channels;
> > > - struct nv_device_info_v1_data runlists;
> > > - } v;
> > > - } args = {
> > > - .m.version = 1,
> > > - .m.count = sizeof(args.v) / sizeof(args.v.channels),
> >
> > sizeof(args.v) == sizeof(struct nv_device_info_v1_data) * 2
> >
> > and sizeof(args.v.channels) == sizeof(struct nv_device_info_v1_data).
> >
> > Isn't this just "2"? i.e. isn't struct nv_device_info_v1::count the
> > counted_by for struct nv_device_info_v1::data?
>
> Yes, it's just `2`. However, I didn't want to explicitly use the magic
> number, in case people don't like it, as in other similar patches (in
> other subsystems).
>
> But, yeah, it's `2`. :)
Okay. So if "count" is set up as a counted_by, the assignment will
happen automatically (in DEFINE_FLEX -- no longer "RAW").
>
> Thanks
> --
> Gustavo
>
> >
> > > - .v.channels.mthd = NV_DEVICE_HOST_CHANNELS,
> > > - .v.runlists.mthd = NV_DEVICE_HOST_RUNLISTS,
> > > - };
> > > + DEFINE_RAW_FLEX(struct nv_device_info_v1, args, data, 2);
> > > + struct nv_device_info_v1_data *channels = &args->data[0];
> > > + struct nv_device_info_v1_data *runlists = &args->data[1];
> > > struct nvif_object *device = &drm->client.device.object;
> > > int ret, i;
> > > - ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, &args, sizeof(args));
> > > + args->version = 1;
> > > + args->count = (__struct_size(args) - sizeof(*args)) /
> > > + sizeof(*args->data);
> > > + channels->mthd = NV_DEVICE_HOST_CHANNELS;
> > > + runlists->mthd = NV_DEVICE_HOST_RUNLISTS;
> > > +
> > > + ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, args,
> > > + __struct_size(args));
> > > if (ret ||
> > > - args.v.runlists.mthd == NV_DEVICE_INFO_INVALID || !args.v.runlists.data ||
> > > - args.v.channels.mthd == NV_DEVICE_INFO_INVALID)
> > > + runlists->mthd == NV_DEVICE_INFO_INVALID || !runlists->data ||
> > > + channels->mthd == NV_DEVICE_INFO_INVALID)
> > > return -ENODEV;
> > > - drm->chan_nr = drm->chan_total = args.v.channels.data;
> > > - drm->runl_nr = fls64(args.v.runlists.data);
> > > + drm->chan_nr = drm->chan_total = channels->data;
> > > + drm->runl_nr = fls64(runlists->data);
> > > drm->runl = kcalloc(drm->runl_nr, sizeof(*drm->runl), GFP_KERNEL);
> > > if (!drm->runl)
> > > return -ENOMEM;
> > > if (drm->chan_nr == 0) {
> > > for (i = 0; i < drm->runl_nr; i++) {
> > > - if (!(args.v.runlists.data & BIT(i)))
> > > + if (!(runlists->data & BIT(i)))
> > > continue;
> > > - args.v.channels.mthd = NV_DEVICE_HOST_RUNLIST_CHANNELS;
> > > - args.v.channels.data = i;
> > > + channels->mthd = NV_DEVICE_HOST_RUNLIST_CHANNELS;
> > > + channels->data = i;
> > > - ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, &args, sizeof(args));
> > > - if (ret || args.v.channels.mthd == NV_DEVICE_INFO_INVALID)
> > > + ret = nvif_object_mthd(device, NV_DEVICE_V0_INFO, args,
> > > + __struct_size(args));
> > > + if (ret || channels->mthd == NV_DEVICE_INFO_INVALID)
> > > return -ENODEV;
> > > - drm->runl[i].chan_nr = args.v.channels.data;
> > > + drm->runl[i].chan_nr = channels->data;
> > > drm->runl[i].chan_id_base = drm->chan_total;
> > > drm->runl[i].context_base = dma_fence_context_alloc(drm->runl[i].chan_nr);
> >
> > Otherwise looks good.
> >
> > -Kees
> >
>
--
Kees Cook
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