drm/radeon: Fix off-by-one power_state index heap overwrite

An out of bounds write happens when setting the default power state.
KASAN sees this as:

[drm] radeon: 512M of GTT memory ready.
[drm] GART: num cpu pages 131072, num gpu pages 131072
==================================================================
BUG: KASAN: slab-out-of-bounds in
radeon_atombios_parse_power_table_1_3+0x1837/0x1998 [radeon]
Write of size 4 at addr ffff88810178d858 by task systemd-udevd/157

CPU: 0 PID: 157 Comm: systemd-udevd Not tainted 5.12.0-E620 #50
Hardware name: eMachines        eMachines E620  /Nile       , BIOS V1.03 09/30/2008
Call Trace:
 dump_stack+0xa5/0xe6
 print_address_description.constprop.0+0x18/0x239
 kasan_report+0x170/0x1a8
 radeon_atombios_parse_power_table_1_3+0x1837/0x1998 [radeon]
 radeon_atombios_get_power_modes+0x144/0x1888 [radeon]
 radeon_pm_init+0x1019/0x1904 [radeon]
 rs690_init+0x76e/0x84a [radeon]
 radeon_device_init+0x1c1a/0x21e5 [radeon]
 radeon_driver_load_kms+0xf5/0x30b [radeon]
 drm_dev_register+0x255/0x4a0 [drm]
 radeon_pci_probe+0x246/0x2f6 [radeon]
 pci_device_probe+0x1aa/0x294
 really_probe+0x30e/0x850
 driver_probe_device+0xe6/0x135
 device_driver_attach+0xc1/0xf8
 __driver_attach+0x13f/0x146
 bus_for_each_dev+0xfa/0x146
 bus_add_driver+0x2b3/0x447
 driver_register+0x242/0x2c1
 do_one_initcall+0x149/0x2fd
 do_init_module+0x1ae/0x573
 load_module+0x4dee/0x5cca
 __do_sys_finit_module+0xf1/0x140
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Without KASAN, this will manifest later when the kernel attempts to
allocate memory that was stomped, since it collides with the inline slab
freelist pointer:

invalid opcode: 0000 [#1] SMP NOPTI
CPU: 0 PID: 781 Comm: openrc-run.sh Tainted: G        W 5.10.12-gentoo-E620 #2
Hardware name: eMachines        eMachines E620  /Nile , BIOS V1.03       09/30/2008
RIP: 0010:kfree+0x115/0x230
Code: 89 c5 e8 75 ea ff ff 48 8b 00 0f ba e0 09 72 63 e8 1f f4 ff ff 41 89 c4 48 8b 45 00 0f ba e0 10 72 0a 48 8b 45 08 a8 01 75 02 <0f> 0b 44 89 e1 48 c7 c2 00 f0 ff ff be 06 00 00 00 48 d3 e2 48 c7
RSP: 0018:ffffb42f40267e10 EFLAGS: 00010246
RAX: ffffd61280ee8d88 RBX: 0000000000000004 RCX: 000000008010000d
RDX: 4000000000000000 RSI: ffffffffba1360b0 RDI: ffffd61280ee8d80
RBP: ffffd61280ee8d80 R08: ffffffffb91bebdf R09: 0000000000000000
R10: ffff8fe2c1047ac8 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000100
FS:  00007fe80eff6b68(0000) GS:ffff8fe339c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe80eec7bc0 CR3: 0000000038012000 CR4: 00000000000006f0
Call Trace:
 __free_fdtable+0x16/0x1f
 put_files_struct+0x81/0x9b
 do_exit+0x433/0x94d
 do_group_exit+0xa6/0xa6
 __x64_sys_exit_group+0xf/0xf
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fe80ef64bea
Code: Unable to access opcode bytes at RIP 0x7fe80ef64bc0.
RSP: 002b:00007ffdb1c47528 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fe80ef64bea
RDX: 00007fe80ef64f60 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 00007fe80ee2c620 R11: 0000000000000246 R12: 00007fe80eff41e0
R13: 00000000ffffffff R14: 0000000000000024 R15: 00007fe80edf9cd0
Modules linked in: radeon(+) ath5k(+) snd_hda_codec_realtek ...

Use a valid power_state index when initializing the "flags" and "misc"
and "misc2" fields.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=211537Reported-by: Erhard F. <erhard_f@mailbox.org>
Fixes: a48b9b4e ("drm/radeon/kms/pm: add asic specific callbacks for getting power state (v2)")
Fixes: 79daedc9 ("drm/radeon/kms: minor pm cleanups")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -2250,10 +2250,10 @@ static int radeon_atombios_parse_power_table_1_3(struct radeon_device *rdev)
 		rdev->pm.default_power_state_index = state_index - 1;
 		rdev->pm.power_state[state_index - 1].default_clock_mode =
 			&rdev->pm.power_state[state_index - 1].clock_info[0];
-		rdev->pm.power_state[state_index].flags &=
+		rdev->pm.power_state[state_index - 1].flags &=
 			~RADEON_PM_STATE_SINGLE_DISPLAY_ONLY;
-		rdev->pm.power_state[state_index].misc = 0;
-		rdev->pm.power_state[state_index].misc2 = 0;
+		rdev->pm.power_state[state_index - 1].misc = 0;
+		rdev->pm.power_state[state_index - 1].misc2 = 0;
 	}
 	return state_index;
 }