nvkm/gsp: correctly advance the read pointer of GSP message queue

In the Linux kernel, the following vulnerability has been resolved:

nvkm/gsp: correctly advance the read pointer of GSP message queue

A GSP event message consists three parts: message header, RPC header,
message body. GSP calculates the number of pages to write from the
total size of a GSP message. This behavior can be observed from the
movement of the write pointer.

However, nvkm takes only the size of RPC header and message body as
the message size when advancing the read pointer. When handling a
two-page GSP message in the non rollback case, It wrongly takes the
message body of the previous message as the message header of the next
message. As the "message length" tends to be zero, in the calculation of
size needs to be copied (0 - size of (message header)), the size needs to
be copied will be "0xffffffxx". It also triggers a kernel panic due to a
NULL pointer error.

[ 547.614102] msg: 00000f90: ff ff ff ff ff ff ff ff 40 d7 18 fb 8b 00 00 00 ........@.......
[ 547.622533] msg: 00000fa0: 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 ................
[ 547.630965] msg: 00000fb0: ff ff ff ff ff ff ff ff 00 00 00 00 ff ff ff ff ................
[ 547.639397] msg: 00000fc0: ff ff ff ff 00 00 00 00 ff ff ff ff ff ff ff ff ................
[ 547.647832] nvkm 0000:c1:00.0: gsp: peek msg rpc fn:0 len:0x0/0xffffffffffffffe0
[ 547.655225] nvkm 0000:c1:00.0: gsp: get msg rpc fn:0 len:0x0/0xffffffffffffffe0
[ 547.662532] BUG: kernel NULL pointer dereference, address: 0000000000000020
[ 547.669485] #PF: supervisor read access in kernel mode
[ 547.674624] #PF: error_code(0x0000) - not-present page
[ 547.679755] PGD 0 P4D 0
[ 547.682294] Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 547.686643] CPU: 22 PID: 322 Comm: kworker/22:1 Tainted: G E 6.9.0-rc6+ #1
[ 547.694893] Hardware name: ASRockRack 1U1G-MILAN/N/ROMED8-NL, BIOS L3.12E 09/06/2022
[ 547.702626] Workqueue: events r535_gsp_msgq_work [nvkm]
[ 547.707921] RIP: 0010:r535_gsp_msg_recv+0x87/0x230 [nvkm]
[ 547.713375] Code: 00 8b 70 08 48 89 e1 31 d2 4c 89 f7 e8 12 f5 ff ff 48 89 c5 48 85 c0 0f 84 cf 00 00 00 48 81 fd 00 f0 ff ff 0f 87 c4 00 00 00 <8b> 55 10 41 8b 46 30 85 d2 0f 85 f6 00 00 00 83 f8 04 76 10 ba 05
[ 547.732119] RSP: 0018:ffffabe440f87e10 EFLAGS: 00010203
[ 547.737335] RAX: 0000000000000010 RBX: 0000000000000008 RCX: 000000000000003f
[ 547.744461] RDX: 0000000000000000 RSI: ffffabe4480a8030 RDI: 0000000000000010
[ 547.751585] RBP: 0000000000000010 R08: 0000000000000000 R09: ffffabe440f87bb0
[ 547.758707] R10: ffffabe440f87dc8 R11: 0000000000000010 R12: 0000000000000000
[ 547.765834] R13: 0000000000000000 R14: ffff9351df1e5000 R15: 0000000000000000
[ 547.772958] FS: 0000000000000000(0000) GS:ffff93708eb00000(0000) knlGS:0000000000000000
[ 547.781035] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 547.786771] CR2: 0000000000000020 CR3: 00000003cc220002 CR4: 0000000000770ef0
[ 547.793896] PKRU: 55555554
[ 547.796600] Call Trace:
[ 547.799046] <TASK>
[ 547.801152] ? __die+0x20/0x70
[ 547.804211] ? page_fault_oops+0x75/0x170
[ 547.808221] ? print_hex_dump+0x100/0x160
[ 547.812226] ? exc_page_fault+0x64/0x150
[ 547.816152] ? asm_exc_page_fault+0x22/0x30
[ 547.820341] ? r535_gsp_msg_recv+0x87/0x230 [nvkm]
[ 547.825184] r535_gsp_msgq_work+0x42/0x50 [nvkm]
[ 547.829845] process_one_work+0x196/0x3d0
[ 547.833861] worker_thread+0x2fc/0x410
[ 547.837613] ? __pfx_worker_thread+0x10/0x10
[ 547.841885] kthread+0xdf/0x110
[ 547.845031] ? __pfx_kthread+0x10/0x10
[ 547.848775] ret_from_fork+0x30/0x50
[ 547.852354] ? __pfx_kthread+0x10/0x10
[ 547.856097] ret_from_fork_asm+0x1a/0x30
[ 547.860019] </TASK>
[ 547.862208] Modules linked in: nvkm(E) gsp_log(E) snd_seq_dummy(E) snd_hrtimer(E) snd_seq(E) snd_timer(E) snd_seq_device(E) snd(E) soundcore(E) rfkill(E) qrtr(E) vfat(E) fat(E) ipmi_ssif(E) amd_atl(E) intel_rapl_msr(E) intel_rapl_common(E) amd64_edac(E) mlx5_ib(E) edac_mce_amd(E) kvm_amd
---truncated---