Hi! Thanks for the catch, just one comment down below

On Fri, 2020-10-09 at 21:11 +0300, Alexander Kapshuk wrote:

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 above. 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: f28e32d3906e 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 being 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 call nouveau_connector_set_edid in the out label 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: f28e32d3906e ("drm/nouveau/kms: Don't change EDID when it hasn't actually changed") Signed-off-by: Alexander Kapshuk alexander.kapshuk@gmail.com

---

drivers/gpu/drm/nouveau/nouveau_connector.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c index 49dd0cbc332f..a3f53d2ac86e 100644 --- a/drivers/gpu/drm/nouveau/nouveau_connector.c +++ b/drivers/gpu/drm/nouveau/nouveau_connector.c @@ -669,8 +669,10 @@ nouveau_connector_detect_lvds(struct drm_connector *connector, bool force) /* Try retrieving EDID via DDC */ if (!drm->vbios.fp_no_ddc) { status = nouveau_connector_detect(connector, force);

• if (status == connector_status_connected)
  

• if (status == connector_status_connected) {
  

• 	edid = nv_connector->edid;
  goto out;
  

• }
  

  }

  /* On some laptops (Sony, i'm looking at you) there appears to

@@ -720,7 +722,8 @@ nouveau_connector_detect_lvds(struct drm_connector *connector, bool force) status = connector_status_unknown; #endif

• nouveau_connector_set_edid(nv_connector, edid);

• if (nv_connector->edid != edid)

• nouveau_connector_set_edid(nv_connector, edid);
  

Could we just update nouveau_connector_set_edid() to do the (nv_connector->edid != edid) check instead of open coding it here?

With that fixed:

Reviewed-by: Lyude Paul lyude@redhat.com

nouveau_connector_set_encoder(connector, nv_encoder); return status; } -- 2.28.0