CVE-2024-26984

In the Linux kernel, the following vulnerability has been resolved:
nouveau: fix instmem race condition around ptr stores Running a lot of VK
CTS in parallel against nouveau, once every few hours you might see
something like this crash. BUG: kernel NULL pointer dereference, address:
0000000000000008 PGD 8000000114e6e067 P4D 8000000114e6e067 PUD 109046067
PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 7 PID: 53891 Comm: deqp-vk Not
tainted 6.8.0-rc6+ #27 Hardware name: Gigabyte Technology Co., Ltd. Z390 I
AORUS PRO WIFI/Z390 I AORUS PRO WIFI-CF, BIOS F8 11/05/2021 RIP:
0010:gp100_vmm_pgt_mem+0xe3/0x180 [nouveau] Code: c7 48 01 c8 49 89 45 58
85 d2 0f 84 95 00 00 00 41 0f b7 46 12 49 8b 7e 08 89 da 42 8d 2c f8 48 8b
47 08 41 83 c7 01 48 89 ee <48> 8b 40 08 ff d0 0f 1f 00 49 8b 7e 08 48 89
d9 48 8d 75 04 48 c1 RSP: 0000:ffffac20c5857838 EFLAGS: 00010202 RAX:
0000000000000000 RBX: 00000000004d8001 RCX: 0000000000000001 RDX:
00000000004d8001 RSI: 00000000000006d8 RDI: ffffa07afe332180 RBP:
00000000000006d8 R08: ffffac20c5857ad0 R09: 0000000000ffff10 R10:
0000000000000001 R11: ffffa07af27e2de0 R12: 000000000000001c R13:
ffffac20c5857ad0 R14: ffffa07a96fe9040 R15: 000000000000001c FS:
00007fe395eed7c0(0000) GS:ffffa07e2c980000(0000) knlGS:0000000000000000 CS:
0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3:
000000011febe001 CR4: 00000000003706f0 DR0: 0000000000000000 DR1:
0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6:
00000000fffe0ff0 DR7: 0000000000000400 Call Trace: … ?
gp100_vmm_pgt_mem+0xe3/0x180 [nouveau] ? gp100_vmm_pgt_mem+0x37/0x180
[nouveau] nvkm_vmm_iter+0x351/0xa20 [nouveau] ?
__pfx_nvkm_vmm_ref_ptes+0x10/0x10 [nouveau] ?
__pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] ?
__pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] ? __lock_acquire+0x3ed/0x2170 ?
__pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau]
nvkm_vmm_ptes_get_map+0xc2/0x100 [nouveau] ?
__pfx_nvkm_vmm_ref_ptes+0x10/0x10 [nouveau] ?
__pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] nvkm_vmm_map_locked+0x224/0x3a0
[nouveau] Adding any sort of useful debug usually makes it go away, so I
hand wrote the function in a line, and debugged the asm. Every so often
pt->memory->ptrs is NULL. This ptrs ptr is set in the nv50_instobj_acquire
called from nvkm_kmap. If Thread A and Thread B both get to
nv50_instobj_acquire around the same time, and Thread A hits the
refcount_set line, and in lockstep thread B succeeds at
refcount_inc_not_zero, there is a chance the ptrs value won’t have been
stored since refcount_set is unordered. Force a memory barrier here, I
picked smp_mb, since we want it on all CPUs and it’s write followed by a
read. v2: use paired smp_rmb/smp_wmb.