Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
Alexander Kapshuk
authored
This oops manifests itself on the following hardware:
01:00.0 VGA compatible controller: NVIDIA Corporation G98M [GeForce G 103M] (rev a1)
Oct 09 14:17:46 lp-sasha kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000
Oct 09 14:17:46 lp-sasha kernel: #PF: supervisor read access in kernel mode
Oct 09 14:17:46 lp-sasha kernel: #PF: error_code(0x0000) - not-present page
Oct 09 14:17:46 lp-sasha kernel: PGD 0 P4D 0
Oct 09 14:17:46 lp-sasha kernel: Oops: 0000 [#1] SMP PTI
Oct 09 14:17:46 lp-sasha kernel: CPU: 1 PID: 191 Comm: systemd-udevd Not tainted 5.9.0-rc8-next-20201009 #38
Oct 09 14:17:46 lp-sasha kernel: Hardware name: Hewlett-Packard Compaq Presario CQ61 Notebook PC/306A, BIOS F.03 03/23/2009
Oct 09 14:17:46 lp-sasha kernel: RIP: 0010:nouveau_connector_detect_depth+0x71/0xc0 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: Code: 0a 00 00 48 8b 49 48 c7 87 b8 00 00 00 06 00 00 00 80 b9 4d 0a 00 00 00 75 1e 83 fa 41 75 05 48 85 c0 75 29 8b 81 10 0d 00 00 <39> 06 7c 25 f6 81 14 0d 00 00 02 75 b7 c3 80 b9 0c 0d 00 00 00 75
Oct 09 14:17:46 lp-sasha kernel: RSP: 0018:ffffc9000028f8c0 EFLAGS: 00010297
Oct 09 14:17:46 lp-sasha kernel: RAX: 0000000000014c08 RBX: ffff8880369d4000 RCX: ffff8880369d3000
Oct 09 14:17:46 lp-sasha kernel: RDX: 0000000000000040 RSI: 0000000000000000 RDI: ffff8880369d4000
Oct 09 14:17:46 lp-sasha kernel: RBP: ffff88800601cc00 R08: ffff8880051da298 R09: ffffffff8226201a
Oct 09 14:17:46 lp-sasha kernel: R10: ffff88800469aa80 R11: ffff888004c84ff8 R12: 0000000000000000
Oct 09 14:17:46 lp-sasha kernel: R13: ffff8880051da000 R14: 0000000000002000 R15: 0000000000000003
Oct 09 14:17:46 lp-sasha kernel: FS: 00007fd0192b3440(0000) GS:ffff8880bc900000(0000) knlGS:0000000000000000
Oct 09 14:17:46 lp-sasha kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Oct 09 14:17:46 lp-sasha kernel: CR2: 0000000000000000 CR3: 0000000004976000 CR4: 00000000000006e0
Oct 09 14:17:46 lp-sasha kernel: Call Trace:
Oct 09 14:17:46 lp-sasha kernel: nouveau_connector_get_modes+0x1e6/0x240 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: ? kfree+0xb9/0x240
Oct 09 14:17:46 lp-sasha kernel: ? drm_connector_list_iter_next+0x7c/0xa0
Oct 09 14:17:46 lp-sasha kernel: drm_helper_probe_single_connector_modes+0x1ba/0x7c0
Oct 09 14:17:46 lp-sasha kernel: drm_client_modeset_probe+0x27e/0x1360
Oct 09 14:17:46 lp-sasha kernel: ? nvif_object_sclass_put+0xc/0x20 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: ? nouveau_cli_init+0x3cc/0x440 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: ? ktime_get_mono_fast_ns+0x49/0xa0
Oct 09 14:17:46 lp-sasha kernel: ? nouveau_drm_open+0x4e/0x180 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: __drm_fb_helper_initial_config_and_unlock+0x3f/0x4a0
Oct 09 14:17:46 lp-sasha kernel: ? drm_file_alloc+0x18f/0x260
Oct 09 14:17:46 lp-sasha kernel: ? mutex_lock+0x9/0x40
Oct 09 14:17:46 lp-sasha kernel: ? drm_client_init+0x110/0x160
Oct 09 14:17:46 lp-sasha kernel: nouveau_fbcon_init+0x14d/0x1c0 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: nouveau_drm_device_init+0x1c0/0x880 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: nouveau_drm_probe+0x11a/0x1e0 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: pci_device_probe+0xcd/0x140
Oct 09 14:17:46 lp-sasha kernel: really_probe+0xd8/0x400
Oct 09 14:17:46 lp-sasha kernel: driver_probe_device+0x4a/0xa0
Oct 09 14:17:46 lp-sasha kernel: device_driver_attach+0x9c/0xc0
Oct 09 14:17:46 lp-sasha kernel: __driver_attach+0x6f/0x100
Oct 09 14:17:46 lp-sasha kernel: ? device_driver_attach+0xc0/0xc0
Oct 09 14:17:46 lp-sasha kernel: bus_for_each_dev+0x75/0xc0
Oct 09 14:17:46 lp-sasha kernel: bus_add_driver+0x106/0x1c0
Oct 09 14:17:46 lp-sasha kernel: driver_register+0x86/0xe0
Oct 09 14:17:46 lp-sasha kernel: ? 0xffffffffa044e000
Oct 09 14:17:46 lp-sasha kernel: do_one_initcall+0x48/0x1e0
Oct 09 14:17:46 lp-sasha kernel: ? _cond_resched+0x11/0x60
Oct 09 14:17:46 lp-sasha kernel: ? kmem_cache_alloc_trace+0x19c/0x1e0
Oct 09 14:17:46 lp-sasha kernel: do_init_module+0x57/0x220
Oct 09 14:17:46 lp-sasha kernel: __do_sys_finit_module+0xa0/0xe0
Oct 09 14:17:46 lp-sasha kernel: do_syscall_64+0x33/0x40
Oct 09 14:17:46 lp-sasha kernel: entry_SYSCALL_64_after_hwframe+0x44/0xa9
Oct 09 14:17:46 lp-sasha kernel: RIP: 0033:0x7fd01a060d5d
Oct 09 14:17:46 lp-sasha kernel: Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d e3 70 0c 00 f7 d8 64 89 01 48
Oct 09 14:17:46 lp-sasha kernel: RSP: 002b:00007ffc8ad38a98 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
Oct 09 14:17:46 lp-sasha kernel: RAX: ffffffffffffffda RBX: 0000563f6e7fd530 RCX: 00007fd01a060d5d
Oct 09 14:17:46 lp-sasha kernel: RDX: 0000000000000000 RSI: 00007fd01a19f95d RDI: 000000000000000f
Oct 09 14:17:46 lp-sasha kernel: RBP: 0000000000020000 R08: 0000000000000000 R09: 0000000000000007
Oct 09 14:17:46 lp-sasha kernel: R10: 000000000000000f R11: 0000000000000246 R12: 00007fd01a19f95d
Oct 09 14:17:46 lp-sasha kernel: R13: 0000000000000000 R14: 0000563f6e7fbc10 R15: 0000563f6e7fd530
Oct 09 14:17:46 lp-sasha kernel: Modules linked in: nouveau(+) ttm xt_string xt_mark xt_LOG vgem v4l2_dv_timings uvcvideo ulpi udf ts_kmp ts_fsm ts_bm snd_aloop sil164 qat_dh895xccvf nf_nat_sip nf_nat_irc nf_nat_ftp nf_nat nf_log_ipv6 nf_log_ipv4 nf_log_common ltc2990 lcd intel_qat input_leds i2c_mux gspca_main videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common videodev mc drivetemp cuse fuse crc_itu_t coretemp ch7006 ath5k ath algif_hash
Oct 09 14:17:46 lp-sasha kernel: CR2: 0000000000000000
Oct 09 14:17:46 lp-sasha kernel: ---[ end trace 0ddafe218ad30017 ]---
Oct 09 14:17:46 lp-sasha kernel: RIP: 0010:nouveau_connector_detect_depth+0x71/0xc0 [nouveau]
Oct 09 14:17:46 lp-sasha kernel: Code: 0a 00 00 48 8b 49 48 c7 87 b8 00 00 00 06 00 00 00 80 b9 4d 0a 00 00 00 75 1e 83 fa 41 75 05 48 85 c0 75 29 8b 81 10 0d 00 00 <39> 06 7c 25 f6 81 14 0d 00 00 02 75 b7 c3 80 b9 0c 0d 00 00 00 75
Oct 09 14:17:46 lp-sasha kernel: RSP: 0018:ffffc9000028f8c0 EFLAGS: 00010297
Oct 09 14:17:46 lp-sasha kernel: RAX: 0000000000014c08 RBX: ffff8880369d4000 RCX: ffff8880369d3000
Oct 09 14:17:46 lp-sasha kernel: RDX: 0000000000000040 RSI: 0000000000000000 RDI: ffff8880369d4000
Oct 09 14:17:46 lp-sasha kernel: RBP: ffff88800601cc00 R08: ffff8880051da298 R09: ffffffff8226201a
Oct 09 14:17:46 lp-sasha kernel: R10: ffff88800469aa80 R11: ffff888004c84ff8 R12: 0000000000000000
Oct 09 14:17:46 lp-sasha kernel: R13: ffff8880051da000 R14: 0000000000002000 R15: 0000000000000003
Oct 09 14:17:46 lp-sasha kernel: FS: 00007fd0192b3440(0000) GS:ffff8880bc900000(0000) knlGS:0000000000000000
Oct 09 14:17:46 lp-sasha kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Oct 09 14:17:46 lp-sasha kernel: CR2: 0000000000000000 CR3: 0000000004976000 CR4: 00000000000006e0
The disassembly:
Code: 0a 00 00 48 8b 49 48 c7 87 b8 00 00 00 06 00 00 00 80 b9 4d 0a 00 00 00 75 1e 83 fa 41 75 05 48 85 c0 75 29 8b 81 10 0d 00 00 <39> 06 7c 25 f6 81 14 0d 00 00 02 75 b7 c3 80 b9 0c 0d 00 00 00 75
All code
========
0: 0a 00 or (%rax),%al
2: 00 48 8b add %cl,-0x75(%rax)
5: 49 rex.WB
6: 48 c7 87 b8 00 00 00 movq $0x6,0xb8(%rdi)
d: 06 00 00 00
11: 80 b9 4d 0a 00 00 00 cmpb $0x0,0xa4d(%rcx)
18: 75 1e jne 0x38
1a: 83 fa 41 cmp $0x41,%edx
1d: 75 05 jne 0x24
1f: 48 85 c0 test %rax,%rax
22: 75 29 jne 0x4d
24: 8b 81 10 0d 00 00 mov 0xd10(%rcx),%eax
2a:* 39 06 cmp %eax,(%rsi) <-- trapping instruction
2c: 7c 25 jl 0x53
2e: f6 81 14 0d 00 00 02 testb $0x2,0xd14(%rcx)
35: 75 b7 jne 0xffffffffffffffee
37: c3 retq
38: 80 b9 0c 0d 00 00 00 cmpb $0x0,0xd0c(%rcx)
3f: 75 .byte 0x75
Code starting with the faulting instruction
===========================================
0: 39 06 cmp %eax,(%rsi)
2: 7c 25 jl 0x29
4: f6 81 14 0d 00 00 02 testb $0x2,0xd14(%rcx)
b: 75 b7 jne 0xffffffffffffffc4
d: c3 retq
e: 80 b9 0c 0d 00 00 00 cmpb $0x0,0xd0c(%rcx)
15: 75 .byte 0x75
objdump -SF --disassemble=nouveau_connector_detect_depth
[...]
if (nv_connector->edid &&
c85e1: 83 fa 41 cmp $0x41,%edx
c85e4: 75 05 jne c85eb <nouveau_connector_detect_depth+0x6b> (File Offset: 0xc866b)
c85e6: 48 85 c0 test %rax,%rax
c85e9: 75 29 jne c8614 <nouveau_connector_detect_depth+0x94> (File Offset: 0xc8694)
nv_connector->type == DCB_CONNECTOR_LVDS_SPWG)
duallink = ((u8 *)nv_connector->edid)[121] == 2;
else
duallink = mode->clock >= bios->fp.duallink_transition_clk;
if ((!duallink && (bios->fp.strapless_is_24bit & 1)) ||
c85eb: 8b 81 10 0d 00 00 mov 0xd10(%rcx),%eax
c85f1: 39 06 cmp %eax,(%rsi)
c85f3: 7c 25 jl c861a <nouveau_connector_detect_depth+0x9a> (File Offset: 0xc869a)
( duallink && (bios->fp.strapless_is_24bit & 2)))
c85f5: f6 81 14 0d 00 00 02 testb $0x2,0xd14(%rcx)
c85fc: 75 b7 jne c85b5 <nouveau_connector_detect_depth+0x35> (File Offset: 0xc8635)
connector->display_info.bpc = 8;
[...]
% scripts/faddr2line /lib/modules/5.9.0-rc8-next-20201009/kernel/drivers/gpu/drm/nouveau/nouveau.ko nouveau_connector_detect_depth+0x71/0xc0
nouveau_connector_detect_depth+0x71/0xc0:
nouveau_connector_detect_depth at /home/sasha/linux-next/drivers/gpu/drm/nouveau/nouveau_connector.c:891
It is actually line 889. See the disassembly below.
889 duallink = mode->clock >= bios->fp.duallink_transition_clk;
The NULL pointer being dereferenced is mode.
Git bisect has identified the following commit as bad:
f28e32d3 drm/nouveau/kms: Don't change EDID when it hasn't actually changed
Here is the chain of events that causes the oops.
On entry to nouveau_connector_detect_lvds, edid is set to NULL. The call
to nouveau_connector_detect sets nv_connector->edid to valid memory,
with status set to connector_status_connected and the flow of execution
branching to the out label.
The subsequent call to nouveau_connector_set_edid erronously clears
nv_connector->edid, via the local edid pointer which remains set to NULL.
Fix this by setting edid to the value of the just acquired
nv_connector->edid and executing the body of nouveau_connector_set_edid
only if nv_connector->edid and edid point to different memory addresses
thus preventing nv_connector->edid from being turned into a dangling
pointer.
Fixes: f28e32d3 ("drm/nouveau/kms: Don't change EDID when it hasn't actually changed")
Signed-off-by: 
Alexander Kapshuk <alexander.kapshuk@gmail.com>
Reviewed-by: 
Lyude Paul <lyude@redhat.com>
Signed-off-by: 
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