[BUG] double fault in amdgpu_discovery_init [amdgpu] [syzkaller]

Hi,

While fuzzing kernel v7.1 with syzkaller, we found a kernel double fault PANIC 
in the amdgpu IP discovery initialization path. The crash was triggered during 
GPU probe on a custom QEMU virtual NAVI14 device.

Kernel PANIC via double fault in `amdgpu_discovery_init()` at
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:635 during IP discovery
table reading. The function triggered a double fault at its entry point
(large stack frame allocation of 0x1358 bytes), causing a PANIC.

The crash occurs at `amdgpu_discovery_init+0x18` — very early in the
function. The trapping instruction is a `call` at offset 0x18, after the
function prologue allocates a large stack frame (`sub $0x1358, %rsp` =
4952 bytes). A double fault at function entry indicates stack corruption
or stack overflow — the large stack allocation may have crossed into an
unmapped guard page, or the stack was already corrupted by anomalous
MMIO responses from the virtual device.

The amdgpu driver's `amdgpu_discovery_init()` function does not validate
the device's IP discovery data sufficiently before proceeding with
stack-intensive operations. The virtual device returned anomalous IP
discovery data, causing memory/stack corruption that led to the double
fault.

- Kernel: 7.1.0 #1 PREEMPT(lazy)
- Hardware: QEMU Standard PC (Q35 + ICH9), virtual NAVI14 (0x1002:0x7340)
- Tainted: G B W O (BAD_PAGE, WARN, OOT_MODULE)

The crash report attached below:

amdgpu 0000:00:05.0: enabling device (0000 -> 0002)
amdgpu 0000:00:05.0: initializing kernel modesetting (NAVI14 0x1002:0x7340 0x1AF4:0x1100 0x00).
amdgpu 0000:00:05.0: register mmio base: 0xFC000000
amdgpu 0000:00:05.0: register mmio size: 33554432
traps: PANIC: double fault, error_code: 0x0
Oops: double fault: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 715 Comm: syz.0.2 Tainted: G    B   W  O        7.1.0 #1 PREEMPT(lazy) 
Tainted: [B]=BAD_PAGE, [W]=WARN, [O]=OOT_MODULE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:amdgpu_discovery_init+0x18/0x87f0 drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:635 [amdgpu]
Code: 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 41 57 41 56 41 54 53 48 81 ec 58 13 00 00 48 89 bc 24 08 13 00 00 31 ff <e8> b3 df b8 f6 48 89 84 24 f0 12 00 00 31 ff e8 54 e3 b8 f6 48 89
RSP: 0018:ffff8880600ff710 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff8880099860c8 RCX: 0000000000100000
RDX: ffffc90004409000 RSI: 00000000000fffff RDI: 0000000000000000
RBP: ffff888060106d48 R08: 0000000000000000 R09: 0000000000000000
R10: ffff888060106c20 R11: ffffed100c020da4 R12: ffff8880099860c8
R13: ffff888009986078 R14: ffff888009986000 R15: ffff888009986000
FS:  000055557874c500(0000) GS:ffff8880e6a8d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8880600ff708 CR3: 00000000694a9000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 amdgpu_driver_load_kms+0x147/0x5c0 drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c:148 [amdgpu]
 </TASK>
Modules linked in: amdgpu(+) ppp_generic slhc gadgetfs udc_core sit tunnel4 ip_tunnel geneve ip6_udp_tunnel udp_tunnel macsec macvtap tap ipvlan macvlan virt_wifi veth nlmon dummy team bonding tun rfuzzer_device(O) i2c_dev iTCO_wdt intel_pmc_bxt ppdev watchdog vga16fb vgastate parport_pc parport gpu_sched drm_panel_backlight_quirks amdxcp drm_exec drm_suballoc_helper lpc_ich mfd_core drm_ttm_helper bochs mousedev serio_raw tpm_tis tpm_tis_core tpm dm_mod dax dmi_sysfs qemu_fw_cfg virtio_rng kt_runtime(O) uio_pci_kerneltracker_driver(O) [last unloaded: amdgpu]
---[ end trace 0000000000000000 ]---
RIP: 0010:amdgpu_discovery_init+0x18/0x87f0 drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:635 [amdgpu]
Code: 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 41 57 41 56 41 54 53 48 81 ec 58 13 00 00 48 89 bc 24 08 13 00 00 31 ff <e8> b3 df b8 f6 48 89 84 24 f0 12 00 00 31 ff e8 54 e3 b8 f6 48 89
RSP: 0018:ffff8880600ff710 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff8880099860c8 RCX: 0000000000100000
RDX: ffffc90004409000 RSI: 00000000000fffff RDI: 0000000000000000
RBP: ffff888060106d48 R08: 0000000000000000 R09: 0000000000000000
R10: ffff888060106c20 R11: ffffed100c020da4 R12: ffff8880099860c8
R13: ffff888009986078 R14: ffff888009986000 R15: ffff888009986000
FS:  000055557874c500(0000) GS:ffff8880e6a8d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8880600ff708 CR3: 00000000694a9000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	66 90                	xchg   %ax,%ax
   2:	90                   	nop
   3:	90                   	nop
   4:	90                   	nop
   5:	90                   	nop
   6:	90                   	nop
   7:	90                   	nop
   8:	90                   	nop
   9:	90                   	nop
   a:	90                   	nop
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop
  10:	90                   	nop
  11:	90                   	nop
  12:	41 57                	push   %r15
  14:	41 56                	push   %r14
  16:	41 54                	push   %r12
  18:	53                   	push   %rbx
  19:	48 81 ec 58 13 00 00 	sub    $0x1358,%rsp
  20:	48 89 bc 24 08 13 00 	mov    %rdi,0x1308(%rsp)
  27:	00
  28:	31 ff                	xor    %edi,%edi
* 2a:	e8 b3 df b8 f6       	call   0xf6b8dfe2 <-- trapping instruction
  2f:	48 89 84 24 f0 12 00 	mov    %rax,0x12f0(%rsp)
  36:	00
  37:	31 ff                	xor    %edi,%edi
  39:	e8 54 e3 b8 f6       	call   0xf6b8e392
  3e:	48                   	rex.W
  3f:	89                   	.byte 0x89

<<<<<<<<<<<<<<< tail report >>>>>>>>>>>>>>>

Regards,
Yang Zi